ABS Failure? Cannot bleed at right front.
04-20-2014, 09:51 PM
#1
Instructor
Thread Starter
ABS Failure? Cannot bleed at right front.
Car - 1988 Base Coupe
Work performed -
Replaced master cylinder, pads on all 4 corners.
-Bench Bled MC
-Installed MC
-Bleed order - RF, RR, LR, LF
-RF didnt seem to bleed well at all, so I moved on.
-RR, LR, RF all bleed out to clean fluid within 5 cycles (me pumping 3 times & hold, helper release bleeder & re-tighten)
-Went back to RF
-Couldnt bleed, pedal never went soft.
-So I removed line from the caliper, pedal never went soft.
-I removed line from steel line, pedal never went soft.
-I started car & with the power brakes & both feet I managed to slowly push the pedal to the floor, enough to flow about 6oz of fluid into the jug.
-But even on the last time, I had to use both feet & a lot of force to get the pedal to the floor.
From what I have researched, everyone says they have replaced the ABS pump (under car behind driver seat) and it has fixed the issue.
seems fairly common on the RF too.
Anyway, since its a big chunk of change, well for me it is.
Does anyone have any other ideas before I am forced to park the car for a while?
Work performed -
Replaced master cylinder, pads on all 4 corners.
-Bench Bled MC
-Installed MC
-Bleed order - RF, RR, LR, LF
-RF didnt seem to bleed well at all, so I moved on.
-RR, LR, RF all bleed out to clean fluid within 5 cycles (me pumping 3 times & hold, helper release bleeder & re-tighten)
-Went back to RF
-Couldnt bleed, pedal never went soft.
-So I removed line from the caliper, pedal never went soft.
-I removed line from steel line, pedal never went soft.
-I started car & with the power brakes & both feet I managed to slowly push the pedal to the floor, enough to flow about 6oz of fluid into the jug.
-But even on the last time, I had to use both feet & a lot of force to get the pedal to the floor.
From what I have researched, everyone says they have replaced the ABS pump (under car behind driver seat) and it has fixed the issue.
seems fairly common on the RF too.
Anyway, since its a big chunk of change, well for me it is.
Does anyone have any other ideas before I am forced to park the car for a while?
04-20-2014, 10:02 PM
#2
Suckin' gas, haulin' ass.
Member Since: Apr 2010
Location: Newport News Virginia
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Remove the line from the abs unit that goes to the RF and blow compressed air through it to eliminate it being the line. If it goes through the line without any issues, you've found where the blockage is.
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raptor003 (03-12-2020)
04-20-2014, 10:52 PM
#4
Melting Slicks
I have the same problem, but with the LF. I'm sure it's the ABS pump (modulator). I tried heating it (nothing too severe) and some penetrating oil in the LF port, all to no avail. Also checked the relays and the controller. It's the pump, the solenoid for that port is frozen. No one (that I could find) rebuilds them, so my (and probably your) only hope is finding a good used one (or bypassing it).
Mine only has 60K on it, but it sat for a few years. That's probably the why.
PS: I did replace the hose first, but that would have been just too easy...
Mine only has 60K on it, but it sat for a few years. That's probably the why.
PS: I did replace the hose first, but that would have been just too easy...
04-21-2014, 12:42 AM
#5
Instructor
When these units fail you still have brakes that work just like normal. You just won't have any ABS action that prevents solid wheel lockup when panic braking. You should also have an abs light showing in your info center. You can still drive the car as per normal and the brakes will feel and work absolutely as per normal just like every other pre 1986 corvette on the road without the abs.
Before either of you opt for the high cost in both parts and labor to replace the ABS unit I suggest you try back flushing the unit.
These are prone to blocking particularly when experiencing a master cylinder seal failure. A small fragment of torn seal gets pushed down one of the ABS feed pipes and lodges in the unit causing a blockage to one of the exiting caliper feeds.The ABS unit it self will still be working fine and can not sense this and therefore does not produce an ABS fail light in the info center.
The answer is to remove the problem circuit brake line from the master cylinder & hydraulically back flush the exiting circuit (connecting at either at the beginning of the caliper hardline or at the ABS). You could try blowing air through it but as the brake pedal has pushed this debris into place with about 1500lb of pressure (particularly after standing on the pedal with both feet) it often requires more than the 120Lb that a standard compressor can produce.
Most good brake shops will have a mobile master cylinder and pedal arrangement fabricated so they can connect it to the caliper brake line and pump brake fluid under high pressure back through the unit in reverse. Usually this can be done in place without having to remove the unit so it can avoid the additional labor cost of having to remove and replace the unit.
If it doesn't work then you have only lost about 30 minutes of additional labor cost but if it does (and it does 99.9% of the time) then you have saved the cost of a good used abs unit ($400 plus) and several labor hours at about $90 an hour.
Best bet would be to get a couple of quotes from 2 or 3 competent brake shops who are familiar with repairing ABS brake systems. If they look at you kinda strangely when you ask about back flushing a blockage then move on until you find someone that knows what you're talking about. There are brake mechanics that just fit new parts and then there are competent ABS brake mechanics that actually fix stuff for a fraction of replacing and installation costs. The latter type can be quite hard to find these days.
Before either of you opt for the high cost in both parts and labor to replace the ABS unit I suggest you try back flushing the unit.
These are prone to blocking particularly when experiencing a master cylinder seal failure. A small fragment of torn seal gets pushed down one of the ABS feed pipes and lodges in the unit causing a blockage to one of the exiting caliper feeds.The ABS unit it self will still be working fine and can not sense this and therefore does not produce an ABS fail light in the info center.
The answer is to remove the problem circuit brake line from the master cylinder & hydraulically back flush the exiting circuit (connecting at either at the beginning of the caliper hardline or at the ABS). You could try blowing air through it but as the brake pedal has pushed this debris into place with about 1500lb of pressure (particularly after standing on the pedal with both feet) it often requires more than the 120Lb that a standard compressor can produce.
Most good brake shops will have a mobile master cylinder and pedal arrangement fabricated so they can connect it to the caliper brake line and pump brake fluid under high pressure back through the unit in reverse. Usually this can be done in place without having to remove the unit so it can avoid the additional labor cost of having to remove and replace the unit.
If it doesn't work then you have only lost about 30 minutes of additional labor cost but if it does (and it does 99.9% of the time) then you have saved the cost of a good used abs unit ($400 plus) and several labor hours at about $90 an hour.
Best bet would be to get a couple of quotes from 2 or 3 competent brake shops who are familiar with repairing ABS brake systems. If they look at you kinda strangely when you ask about back flushing a blockage then move on until you find someone that knows what you're talking about. There are brake mechanics that just fit new parts and then there are competent ABS brake mechanics that actually fix stuff for a fraction of replacing and installation costs. The latter type can be quite hard to find these days.
Last edited by Cruizin; 04-21-2014 at 12:53 AM.
04-21-2014, 05:34 AM
#6
Instructor
Thread Starter
Cruizin -
It makes a lot of sense what your saying - and if that is the case, I wonder if any debris could have been pushed all the way to the ABS unit.
There are no flow restrictions between the MC & the ABS unit, and when I had the line disconnected at the RF wheel, there were no flow restrictions after it.
My goal with putting so much pressure on the pedal was to push any debris through the line, I pushed about 6oz or approx 350ml through the line, so I would think I have pushed any possible debris to the ABS unit.
I am going to try disconnecting the line from the MC to the ABS unit (At the ABS end) and see if pressure flows there fine.
Then I will check the line from the ABS to the RF wheel.
If those check out fine I guess I will remove the ABS unit & inspect it. maybe any debris has been trapped there.
It makes a lot of sense what your saying - and if that is the case, I wonder if any debris could have been pushed all the way to the ABS unit.
There are no flow restrictions between the MC & the ABS unit, and when I had the line disconnected at the RF wheel, there were no flow restrictions after it.
My goal with putting so much pressure on the pedal was to push any debris through the line, I pushed about 6oz or approx 350ml through the line, so I would think I have pushed any possible debris to the ABS unit.
I am going to try disconnecting the line from the MC to the ABS unit (At the ABS end) and see if pressure flows there fine.
Then I will check the line from the ABS to the RF wheel.
If those check out fine I guess I will remove the ABS unit & inspect it. maybe any debris has been trapped there.
04-21-2014, 06:08 AM
#7
Instructor
"I wonder if any debris could have been pushed all the way to the ABS unit."
"so I would think I have pushed any possible debris to the ABS unit."
I am saying your blockage is almost guaranteed to be inside the ABS unit . There are several restrictions within the unit that will not let a piece of debris pass through it. The debris lodges against the restriction sealing off the flow. You can however back flush it out the same way it came in.
"I am going to try disconnecting the line from the MC to the ABS unit (At the ABS end) and see if pressure flows there fine.
Then I will check the line from the ABS to the RF wheel."
You will be making a lot of messy work for your self by disconnecting the line in multiple stages. You risk getting brake fluid inside your car, over your upholstery and your paint work. Simply back flush the entire circuit in one action. Remove the appropriate steel line at the MC and put a length of plastic or rubber hose over the end and tape it up so it can't leak all over your engine bay. Put the other end of the hose into a large bottle on the floor with a rag tied around the neck so it can vent the pressure but avoid a pressure explosion of brake fluid should the blockage let go with a bang drenching you, your garage and your car . Apply pressure into the brake line at the wheel end by removing the flexible hose and attaching a line with the correct thread fitting. Apply pressure straight into the beginning of the steel line and you will clear the entire line right back to the MC in one clean action.
As I said you could need up to 1500lb pressure to push it out so accomplishing this with compressed air is possible but doubtful. I have done this several times on various ABS units over the years without having to remove the units and all the messy fiddly work that involves.
Edit: forgot to mention that you can do this yourself if you want to make up a temp brake line and run it from your MC to the caliper end of the blocked circuit. You'll need to take your time bleeding out the air.
"so I would think I have pushed any possible debris to the ABS unit."
I am saying your blockage is almost guaranteed to be inside the ABS unit . There are several restrictions within the unit that will not let a piece of debris pass through it. The debris lodges against the restriction sealing off the flow. You can however back flush it out the same way it came in.
"I am going to try disconnecting the line from the MC to the ABS unit (At the ABS end) and see if pressure flows there fine.
Then I will check the line from the ABS to the RF wheel."
You will be making a lot of messy work for your self by disconnecting the line in multiple stages. You risk getting brake fluid inside your car, over your upholstery and your paint work. Simply back flush the entire circuit in one action. Remove the appropriate steel line at the MC and put a length of plastic or rubber hose over the end and tape it up so it can't leak all over your engine bay. Put the other end of the hose into a large bottle on the floor with a rag tied around the neck so it can vent the pressure but avoid a pressure explosion of brake fluid should the blockage let go with a bang drenching you, your garage and your car . Apply pressure into the brake line at the wheel end by removing the flexible hose and attaching a line with the correct thread fitting. Apply pressure straight into the beginning of the steel line and you will clear the entire line right back to the MC in one clean action.
As I said you could need up to 1500lb pressure to push it out so accomplishing this with compressed air is possible but doubtful. I have done this several times on various ABS units over the years without having to remove the units and all the messy fiddly work that involves.
Edit: forgot to mention that you can do this yourself if you want to make up a temp brake line and run it from your MC to the caliper end of the blocked circuit. You'll need to take your time bleeding out the air.
Last edited by Cruizin; 04-21-2014 at 10:59 AM.
04-21-2014, 10:14 AM
#8
Le Mans Master
Car - 1988 Base Coupe
Work performed -
Replaced master cylinder, pads on all 4 corners.
-Bench Bled MC
-Installed MC
-Bleed order - RF, RR, LR, LF
-RF didnt seem to bleed well at all, so I moved on.
-RR, LR, RF all bleed out to clean fluid within 5 cycles (me pumping 3 times & hold, helper release bleeder & re-tighten)
-Went back to RF
-Couldnt bleed, pedal never went soft.
-So I removed line from the caliper, pedal never went soft.
-I removed line from steel line, pedal never went soft.
-I started car & with the power brakes & both feet I managed to slowly push the pedal to the floor, enough to flow about 6oz of fluid into the jug.
-But even on the last time, I had to use both feet & a lot of force to get the pedal to the floor.
From what I have researched, everyone says they have replaced the ABS pump (under car behind driver seat) and it has fixed the issue.
seems fairly common on the RF too.
Anyway, since its a big chunk of change, well for me it is.
Does anyone have any other ideas before I am forced to park the car for a while?
Work performed -
Replaced master cylinder, pads on all 4 corners.
-Bench Bled MC
-Installed MC
-Bleed order - RF, RR, LR, LF
-RF didnt seem to bleed well at all, so I moved on.
-RR, LR, RF all bleed out to clean fluid within 5 cycles (me pumping 3 times & hold, helper release bleeder & re-tighten)
-Went back to RF
-Couldnt bleed, pedal never went soft.
-So I removed line from the caliper, pedal never went soft.
-I removed line from steel line, pedal never went soft.
-I started car & with the power brakes & both feet I managed to slowly push the pedal to the floor, enough to flow about 6oz of fluid into the jug.
-But even on the last time, I had to use both feet & a lot of force to get the pedal to the floor.
From what I have researched, everyone says they have replaced the ABS pump (under car behind driver seat) and it has fixed the issue.
seems fairly common on the RF too.
Anyway, since its a big chunk of change, well for me it is.
Does anyone have any other ideas before I am forced to park the car for a while?
These ABS units do go bad and clog as there are many threads on this I have seen over the years. They do clog and will affect your primary braking especially in a panic stop. I can't tell you if a bad ABS will affect the ABS action of the pump and unit. But if there is a clogged line out of it, who cares at that point if the pump is running (its not going to help braking).
Chances of finding a clogged hard line, well is..........
04-21-2014, 07:20 PM
#9
Instructor
Thread Starter
Update 4-21
I disconnected the hard line from the ABS unit behind the drivers seat, I can flow fluid through the LF port like you would expect from any disconnected line.
I cannot flow fluid through the RF port without excessive pedal force.
So that tells me that there is a blockage inside the ABS unit.
Im going to yank it out tomorrow & see what I can see.
This car sat for a little over a year before I got it, so I guess a stuck or blocked valve in the ABS unit is not out of the question.
I disconnected the hard line from the ABS unit behind the drivers seat, I can flow fluid through the LF port like you would expect from any disconnected line.
I cannot flow fluid through the RF port without excessive pedal force.
So that tells me that there is a blockage inside the ABS unit.
Im going to yank it out tomorrow & see what I can see.
This car sat for a little over a year before I got it, so I guess a stuck or blocked valve in the ABS unit is not out of the question.
04-21-2014, 09:16 PM
#10
Instructor
Update 4-21
I disconnected the hard line from the ABS unit behind the drivers seat, I can flow fluid through the LF port like you would expect from any disconnected line.
I cannot flow fluid through the RF port without excessive pedal force.
So that tells me that there is a blockage inside the ABS unit.
Im going to yank it out tomorrow & see what I can see.
This car sat for a little over a year before I got it, so I guess a stuck or blocked valve in the ABS unit is not out of the question.
I disconnected the hard line from the ABS unit behind the drivers seat, I can flow fluid through the LF port like you would expect from any disconnected line.
I cannot flow fluid through the RF port without excessive pedal force.
So that tells me that there is a blockage inside the ABS unit.
Im going to yank it out tomorrow & see what I can see.
This car sat for a little over a year before I got it, so I guess a stuck or blocked valve in the ABS unit is not out of the question.
However a failed relay will just not close the valves meaning no abs action - braking will remain operational otherwise and you should have an abs warning light showing.
Your problem most likely came from pushing a piece of torn MC seal through the system when you bleed the brakes (before replacing the MC), After sitting for a long length of time these seals can stick and tear the first time you push the brake pedal.
If you go pocking bits of wire through the pump unit you risk permanent valve damage. Lumps of rubbish in the system can and do block the open valve orifice so a good back flush with high pressure fluid is your potential cure.
Last edited by Cruizin; 04-21-2014 at 09:23 PM.
04-26-2014, 12:04 PM
#11
Racer
Member Since: Mar 2012
Location: East Windsor New Jersey
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Glad I found this as I'm having the same issue. LF caliper locks. Being told it's the pump modulator and this car sat for around 4 years before I bought it. I found an abs pump with little miles on it so I'll replace it. But how often do these go when using the car normally? I drive mine quite a bit.
Sorry, don't mean to high jack the thread. Just looking for a quick answer.
OP, if you're still looking for one I know Black Z51 is selling his for a very low price. I was going to buy it as a spare but if you're needing one then contact him.
Chuck
Sorry, don't mean to high jack the thread. Just looking for a quick answer.
OP, if you're still looking for one I know Black Z51 is selling his for a very low price. I was going to buy it as a spare but if you're needing one then contact him.
Chuck
04-26-2014, 12:22 PM
#12
Instructor
Thread Starter
Glad I found this as I'm having the same issue. LF caliper locks. Being told it's the pump modulator and this car sat for around 4 years before I bought it. I found an abs pump with little miles on it so I'll replace it. But how often do these go when using the car normally? I drive mine quite a bit.
Sorry, don't mean to high jack the thread. Just looking for a quick answer.
OP, if you're still looking for one I know Black Z51 is selling his for a very low price. I was going to buy it as a spare but if you're needing one then contact him.
Chuck
Sorry, don't mean to high jack the thread. Just looking for a quick answer.
OP, if you're still looking for one I know Black Z51 is selling his for a very low price. I was going to buy it as a spare but if you're needing one then contact him.
Chuck
What I ended up doing was bypassing the ABS unit, I got some fittings & set the brakes up like any 'normal' car without ABS.
I did this so I could verify the operation of the brakes, I didnt want to replace the ABS unit until I knew without a doubt that it was the culprit.
I will replace the ABS unit, I am going this afternoon to meet a local guy who is parting an 88 vert, so I am hoping to get a package deal on a few things Im needing.
I read so many opinions on this issue, and many people want to say that the ABS unit cant cause your brakes to lock/rub etc. but I can assure you first hand - the ABS pump CAN cause brake failure.
However, I will state that the unit is unlikely to cause issues unless something foreign is introduced.
Mine has a valve stuck closed, not allowing any pressure to flow through the front right port. most likely caused by a master cylinder seal failure. junk pushed down the line to the ABS uint.
The orifices inside the ABS valves are incredibly small, and would be quite easy to block.
NOTE: If you want to try bypassing the ABS unit - make sure you get "Metric Bubble Flare" fittings. there are some that look the same, but if you use the wrong type of flare fitting they will not hold the pressure & could cause serious brake failure.
Last edited by aussie_g; 04-26-2014 at 12:29 PM.
04-27-2014, 01:43 PM
#13
Instructor
Thread Starter
OK, if anyone wants to do this. here is the info...
Get 2 of these
http://www.appletreeauto.com/METRIC-...E-113-611-755/
You will need an extra caliper bleeder fitting. I replaced all of mine with speed bleeders so I had extra's.
1. Remove drivers seat (Not necessary, but VERY helpful)
2. climb in the car with a 12mm & a 15mm wrench, some paper towels, 2 'TEE' fittings & a bleeder fitting.
3. open your rear storage box & remove the black coated insulation peice.
4. remove the 2 hard lines from the passenger side of the ABS unit.
5. turn the bottom of the two lines up (vertical) and screw into one side of the 'TEE'
6.screw the upper line into the 'TEE'
7.screw the bleeder fitting into the third open port in the 'TEE'
8.Use the 15mm wrench to hold the 'TEE' fitting & use your 12mm wrench to tighten the brake line fittings & the bleeder fitting.
9. remove the 3 hard lines from the drivers side of the ABS unit.
10. twist the hard lines (gently) to line them up with the 'TEE' fitting and screw them in. (I chose to put the incoming line into the bottom of the 'TEE' then the 2 outgoing lines into the sides)
11. Use the 15mm wrench to hold the 'TEE' and tighten the 3 fittings with your 12mm wrench.
12. Disconnect the electrical connector with the one big red wire.
13. Put all the stuff back together, bleed your brakes (RF, LF, RR, LR)
Start the engine & put constant pressure on your bake pedal, making sure it stays in place.
If the pedal slowly sinks to the floor, then you have a leak.
FINE PRINT: This is bypassing your factory ABS, your car WILL NOT have ABS anymore, perform this at your own risk.
I only did this to verify that my entire brake system was performing properly before replacing the ABS unit.
It is NOT a permanent fix. unless its a track only car.
Get 2 of these
http://www.appletreeauto.com/METRIC-...E-113-611-755/
You will need an extra caliper bleeder fitting. I replaced all of mine with speed bleeders so I had extra's.
1. Remove drivers seat (Not necessary, but VERY helpful)
2. climb in the car with a 12mm & a 15mm wrench, some paper towels, 2 'TEE' fittings & a bleeder fitting.
3. open your rear storage box & remove the black coated insulation peice.
4. remove the 2 hard lines from the passenger side of the ABS unit.
5. turn the bottom of the two lines up (vertical) and screw into one side of the 'TEE'
6.screw the upper line into the 'TEE'
7.screw the bleeder fitting into the third open port in the 'TEE'
8.Use the 15mm wrench to hold the 'TEE' fitting & use your 12mm wrench to tighten the brake line fittings & the bleeder fitting.
9. remove the 3 hard lines from the drivers side of the ABS unit.
10. twist the hard lines (gently) to line them up with the 'TEE' fitting and screw them in. (I chose to put the incoming line into the bottom of the 'TEE' then the 2 outgoing lines into the sides)
11. Use the 15mm wrench to hold the 'TEE' and tighten the 3 fittings with your 12mm wrench.
12. Disconnect the electrical connector with the one big red wire.
13. Put all the stuff back together, bleed your brakes (RF, LF, RR, LR)
Start the engine & put constant pressure on your bake pedal, making sure it stays in place.
If the pedal slowly sinks to the floor, then you have a leak.
FINE PRINT: This is bypassing your factory ABS, your car WILL NOT have ABS anymore, perform this at your own risk.
I only did this to verify that my entire brake system was performing properly before replacing the ABS unit.
It is NOT a permanent fix. unless its a track only car.
Last edited by aussie_g; 04-27-2014 at 01:47 PM.
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M.B.H. (09-21-2022)
12-09-2015, 01:45 PM
#15
Burning Brakes
OK, if anyone wants to do this. here is the info...
Get 2 of these
http://www.appletreeauto.com/METRIC-...E-113-611-755/
You will need an extra caliper bleeder fitting. I replaced all of mine with speed bleeders so I had extra's.
1. Remove drivers seat (Not necessary, but VERY helpful)
2. climb in the car with a 12mm & a 15mm wrench, some paper towels, 2 'TEE' fittings & a bleeder fitting.
3. open your rear storage box & remove the black coated insulation peice.
4. remove the 2 hard lines from the passenger side of the ABS unit.
5. turn the bottom of the two lines up (vertical) and screw into one side of the 'TEE'
6.screw the upper line into the 'TEE'
7.screw the bleeder fitting into the third open port in the 'TEE'
8.Use the 15mm wrench to hold the 'TEE' fitting & use your 12mm wrench to tighten the brake line fittings & the bleeder fitting.
9. remove the 3 hard lines from the drivers side of the ABS unit.
10. twist the hard lines (gently) to line them up with the 'TEE' fitting and screw them in. (I chose to put the incoming line into the bottom of the 'TEE' then the 2 outgoing lines into the sides)
11. Use the 15mm wrench to hold the 'TEE' and tighten the 3 fittings with your 12mm wrench.
12. Disconnect the electrical connector with the one big red wire.
13. Put all the stuff back together, bleed your brakes (RF, LF, RR, LR)
Start the engine & put constant pressure on your bake pedal, making sure it stays in place.
If the pedal slowly sinks to the floor, then you have a leak.
FINE PRINT: This is bypassing your factory ABS, your car WILL NOT have ABS anymore, perform this at your own risk.
I only did this to verify that my entire brake system was performing properly before replacing the ABS unit.
It is NOT a permanent fix. unless its a track only car.
Get 2 of these
http://www.appletreeauto.com/METRIC-...E-113-611-755/
You will need an extra caliper bleeder fitting. I replaced all of mine with speed bleeders so I had extra's.
1. Remove drivers seat (Not necessary, but VERY helpful)
2. climb in the car with a 12mm & a 15mm wrench, some paper towels, 2 'TEE' fittings & a bleeder fitting.
3. open your rear storage box & remove the black coated insulation peice.
4. remove the 2 hard lines from the passenger side of the ABS unit.
5. turn the bottom of the two lines up (vertical) and screw into one side of the 'TEE'
6.screw the upper line into the 'TEE'
7.screw the bleeder fitting into the third open port in the 'TEE'
8.Use the 15mm wrench to hold the 'TEE' fitting & use your 12mm wrench to tighten the brake line fittings & the bleeder fitting.
9. remove the 3 hard lines from the drivers side of the ABS unit.
10. twist the hard lines (gently) to line them up with the 'TEE' fitting and screw them in. (I chose to put the incoming line into the bottom of the 'TEE' then the 2 outgoing lines into the sides)
11. Use the 15mm wrench to hold the 'TEE' and tighten the 3 fittings with your 12mm wrench.
12. Disconnect the electrical connector with the one big red wire.
13. Put all the stuff back together, bleed your brakes (RF, LF, RR, LR)
Start the engine & put constant pressure on your bake pedal, making sure it stays in place.
If the pedal slowly sinks to the floor, then you have a leak.
FINE PRINT: This is bypassing your factory ABS, your car WILL NOT have ABS anymore, perform this at your own risk.
I only did this to verify that my entire brake system was performing properly before replacing the ABS unit.
It is NOT a permanent fix. unless its a track only car.
12-10-2015, 10:09 PM
#16
Instructor
Yeah Aussie-g, that was a great write up.
I think it worth mentioning that converting your braking system back to non ABS is not dangerous if you do the job properly. Aussie-g's method could quite safely be left as a permanent system. You could also remove the entire ABS system and reroute the brake lines back to the 1985 layout.
There are plenty of early 1000hp plus muscle cars on the road that are pre ABS. With larger disc units fitted they will out stop any stock C4 with ABS under normal circumstances. You won't find many of these muscle car owners bother to install ABS systems even in high dollar pro stock road cars.
The ABS is of course an advantage so don't misunderstand me but your braking is not reduced to dangerous or grossly inferior just by cutting it out of the system.
Are any pre 86 Corvettes known for having dangerous brakes simply because they are not ABS?
The day may come when C4 ABS pumps and parts get near impossible to find so Aussie-g's get-a-round may become the only way to keep these cars on the road at reasonable cost.
I think it worth mentioning that converting your braking system back to non ABS is not dangerous if you do the job properly. Aussie-g's method could quite safely be left as a permanent system. You could also remove the entire ABS system and reroute the brake lines back to the 1985 layout.
There are plenty of early 1000hp plus muscle cars on the road that are pre ABS. With larger disc units fitted they will out stop any stock C4 with ABS under normal circumstances. You won't find many of these muscle car owners bother to install ABS systems even in high dollar pro stock road cars.
The ABS is of course an advantage so don't misunderstand me but your braking is not reduced to dangerous or grossly inferior just by cutting it out of the system.
Are any pre 86 Corvettes known for having dangerous brakes simply because they are not ABS?
The day may come when C4 ABS pumps and parts get near impossible to find so Aussie-g's get-a-round may become the only way to keep these cars on the road at reasonable cost.
12-11-2015, 01:39 PM
#17
Racer
Cruizin:
I have a similar problem to OP, except my brakes pull noticeably to the left when applied. (Front left caliper does not bleed well)
I replaced the 2 bosh relays, I get a 3 blinks from ABS light on startup and the pump runs @4mph. Except now my pump will apply randomly at stop signs and the dash light does not come on.*
Would a back flush of the system help me? I was going to clean up my sensors from debris next.
I'd really like to have ABS functioning but this pulling and erratic pump is really worrying me. I'm really interested to hear whats going on!
*I did just replace 1 rear wheel hub and haven't had time to do the other, right around when I started having this problem with the erratic pump with no ABS light.
I have a similar problem to OP, except my brakes pull noticeably to the left when applied. (Front left caliper does not bleed well)
I replaced the 2 bosh relays, I get a 3 blinks from ABS light on startup and the pump runs @4mph. Except now my pump will apply randomly at stop signs and the dash light does not come on.*
Would a back flush of the system help me? I was going to clean up my sensors from debris next.
I'd really like to have ABS functioning but this pulling and erratic pump is really worrying me. I'm really interested to hear whats going on!
*I did just replace 1 rear wheel hub and haven't had time to do the other, right around when I started having this problem with the erratic pump with no ABS light.
Last edited by 21boy; 12-11-2015 at 01:45 PM.
12-12-2015, 12:58 AM
#18
Instructor
21boy
If your car is pulling to the left then this suggests the problem is with your right front brake.
Unequal braking force will pull the car in the direction of the working brake - not the other way around.
I'd start by making sure you are getting fluid pressure at the RH front caliper by bleeding and checking for trapped air at the same time. This could cause the car to veer to the left as it both delays and potentially reduces the pressure at the caliper.
If you can't get a strong flow of fluid then your flexible connecting hose or the ABS becomes suspect. Remove your caliper flexible hose where it joins the hardline and check for flow. If nothing then slacken the RH front feed line where it exits the ABS unit (behind the drivers seat) and check for fluid escaping (messy business).
Diagram of brake line locations on the ABS valve body in this thread (post.6): https://www.corvetteforum.com/forums...tor-valve.html
If nothing then you either have an internal blockage which a good back flush may correct or you may have a stuck valve for the RH front circuit. Its not common but does happen.
If you have a stuck valve you will not be able to pass any fluid through the unit in either direction as the sliding valve ensures the passages are completely cutoff. If this is the case you will need to replace the entire pump/modulator unit as they are not considered serviceable.
If you have good fluid flow at the caliper bleeder nipple then the ABS is unlikely to be the issue. Check for a frozen caliper piston or binding on the caliper sliders/pins.
As regards the pump activating randomly this suggests you have a control module issue. The pump should not run unless you have made a strong braking action enough to activate the ABS (pulsating action felt through the brake peddle). The dash ABS light will not come on as the unit considers its self to be working - albeit incorrectly.
The ABS moves the solenoid valves (one for each front wheel and just one for both back wheels) to stop further pressure to the skidding wheel and then releases the pressure to an accumulator chamber to release the brake.
The accumulator chamber only holds about 2cc of fluid so when the control module senses it is full it activates the pump to empty the accumulator and return the fluid into the master cylinder feed pipe. This all happens in in rapid succession causing the pedal to pulsate.
This is the only time the pump should run as it serves no other purpose.
Therefore the pump should only run under extreme braking. Since you say this occurs at stop signs I'm assuming you have an automatic where you are holding your foot on the brake pedal to stop creeping forward.
The control module receives a signal from the brake peddle stop light switch when you apply the brakes which activates the unit. This signal may be incorrectly activating the pump without the required signal from a full accumulator. However, there are also a number of other issues that could be the problem.
Unfortunately it becomes a job for a brake shop or auto electrician to isolate the issue at this point as you ideally need a J-35890 ABS tester which unfortunately are not common anymore.
However, after paying for this diagnosis chances are all that can be done is the replacing of pump/valve body and or control module.
If you can find a reasonably priced control module that you know is in good working order then that would be my initial recommendation subject to whether the ABS is blocked (and clearable) or has a stuck valve.
If its a stuck valve then you would most likely be better off financially purchasing a complete working unit with modulator valve body(which includes the pump) and control module all from the same car.
Or of course, you could just delete the ABS as I mentioned above. It all comes down to time and dollars.
If your car is pulling to the left then this suggests the problem is with your right front brake.
Unequal braking force will pull the car in the direction of the working brake - not the other way around.
I'd start by making sure you are getting fluid pressure at the RH front caliper by bleeding and checking for trapped air at the same time. This could cause the car to veer to the left as it both delays and potentially reduces the pressure at the caliper.
If you can't get a strong flow of fluid then your flexible connecting hose or the ABS becomes suspect. Remove your caliper flexible hose where it joins the hardline and check for flow. If nothing then slacken the RH front feed line where it exits the ABS unit (behind the drivers seat) and check for fluid escaping (messy business).
Diagram of brake line locations on the ABS valve body in this thread (post.6): https://www.corvetteforum.com/forums...tor-valve.html
If nothing then you either have an internal blockage which a good back flush may correct or you may have a stuck valve for the RH front circuit. Its not common but does happen.
If you have a stuck valve you will not be able to pass any fluid through the unit in either direction as the sliding valve ensures the passages are completely cutoff. If this is the case you will need to replace the entire pump/modulator unit as they are not considered serviceable.
If you have good fluid flow at the caliper bleeder nipple then the ABS is unlikely to be the issue. Check for a frozen caliper piston or binding on the caliper sliders/pins.
As regards the pump activating randomly this suggests you have a control module issue. The pump should not run unless you have made a strong braking action enough to activate the ABS (pulsating action felt through the brake peddle). The dash ABS light will not come on as the unit considers its self to be working - albeit incorrectly.
The ABS moves the solenoid valves (one for each front wheel and just one for both back wheels) to stop further pressure to the skidding wheel and then releases the pressure to an accumulator chamber to release the brake.
The accumulator chamber only holds about 2cc of fluid so when the control module senses it is full it activates the pump to empty the accumulator and return the fluid into the master cylinder feed pipe. This all happens in in rapid succession causing the pedal to pulsate.
This is the only time the pump should run as it serves no other purpose.
Therefore the pump should only run under extreme braking. Since you say this occurs at stop signs I'm assuming you have an automatic where you are holding your foot on the brake pedal to stop creeping forward.
The control module receives a signal from the brake peddle stop light switch when you apply the brakes which activates the unit. This signal may be incorrectly activating the pump without the required signal from a full accumulator. However, there are also a number of other issues that could be the problem.
Unfortunately it becomes a job for a brake shop or auto electrician to isolate the issue at this point as you ideally need a J-35890 ABS tester which unfortunately are not common anymore.
However, after paying for this diagnosis chances are all that can be done is the replacing of pump/valve body and or control module.
If you can find a reasonably priced control module that you know is in good working order then that would be my initial recommendation subject to whether the ABS is blocked (and clearable) or has a stuck valve.
If its a stuck valve then you would most likely be better off financially purchasing a complete working unit with modulator valve body(which includes the pump) and control module all from the same car.
Or of course, you could just delete the ABS as I mentioned above. It all comes down to time and dollars.
Last edited by Cruizin; 12-12-2015 at 01:39 AM.
12-12-2015, 10:18 AM
#19
you can also try excercising the abs pump.
i bled my 87. then went to gravel road and excersied the abs pump.
bled again, more crap came out of lines but the pump purged iself and was filled with fresh clean fluid. worth a try.
when at track pull abs fuse. it will kill u.
http://youtu.be/JCjxjBehpt8
i bled my 87. then went to gravel road and excersied the abs pump.
bled again, more crap came out of lines but the pump purged iself and was filled with fresh clean fluid. worth a try.
when at track pull abs fuse. it will kill u.
http://youtu.be/JCjxjBehpt8
21boy
If your car is pulling to the left then this suggests the problem is with your right front brake.
Unequal braking force will pull the car in the direction of the working brake - not the other way around.
I'd start by making sure you are getting fluid pressure at the RH front caliper by bleeding and checking for trapped air at the same time. This could cause the car to veer to the left as it both delays and potentially reduces the pressure at the caliper.
If you can't get a strong flow of fluid then your flexible connecting hose or the ABS becomes suspect. Remove your caliper flexible hose where it joins the hardline and check for flow. If nothing then slacken the RH front feed line where it exits the ABS unit (behind the drivers seat) and check for fluid escaping (messy business).
Diagram of brake line locations on the ABS valve body in this thread (post.6): https://www.corvetteforum.com/forums...tor-valve.html
If nothing then you either have an internal blockage which a good back flush may correct or you may have a stuck valve for the RH front circuit. Its not common but does happen.
If you have a stuck valve you will not be able to pass any fluid through the unit in either direction as the sliding valve ensures the passages are completely cutoff. If this is the case you will need to replace the entire pump/modulator unit as they are not considered serviceable.
If you have good fluid flow at the caliper bleeder nipple then the ABS is unlikely to be the issue. Check for a frozen caliper piston or binding on the caliper sliders/pins.
As regards the pump activating randomly this suggests you have a control module issue. The pump should not run unless you have made a strong braking action enough to activate the ABS (pulsating action felt through the brake peddle). The dash ABS light will not come on as the unit considers its self to be working - albeit incorrectly.
The ABS moves the solenoid valves (one for each front wheel and just one for both back wheels) to stop further pressure to the skidding wheel and then releases the pressure to an accumulator chamber to release the brake.
The accumulator chamber only holds about 2cc of fluid so when the control module senses it is full it activates the pump to empty the accumulator and return the fluid into the master cylinder feed pipe. This all happens in in rapid succession causing the pedal to pulsate.
This is the only time the pump should run as it serves no other purpose.
Therefore the pump should only run under extreme braking. Since you say this occurs at stop signs I'm assuming you have an automatic where you are holding your foot on the brake pedal to stop creeping forward.
The control module receives a signal from the brake peddle stop light switch when you apply the brakes which activates the unit. This signal may be incorrectly activating the pump without the required signal from a full accumulator. However, there are also a number of other issues that could be the problem.
Unfortunately it becomes a job for a brake shop or auto electrician to isolate the issue at this point as you ideally need a J-35890 ABS tester which unfortunately are not common anymore.
However, after paying for this diagnosis chances are all that can be done is the replacing of pump/valve body and or control module.
If you can find a reasonably priced control module that you know is in good working order then that would be my initial recommendation subject to whether the ABS is blocked (and clearable) or has a stuck valve.
If its a stuck valve then you would most likely be better off financially purchasing a complete working unit with modulator valve body(which includes the pump) and control module all from the same car.
Or of course, you could just delete the ABS as I mentioned above. It all comes down to time and dollars.
If your car is pulling to the left then this suggests the problem is with your right front brake.
Unequal braking force will pull the car in the direction of the working brake - not the other way around.
I'd start by making sure you are getting fluid pressure at the RH front caliper by bleeding and checking for trapped air at the same time. This could cause the car to veer to the left as it both delays and potentially reduces the pressure at the caliper.
If you can't get a strong flow of fluid then your flexible connecting hose or the ABS becomes suspect. Remove your caliper flexible hose where it joins the hardline and check for flow. If nothing then slacken the RH front feed line where it exits the ABS unit (behind the drivers seat) and check for fluid escaping (messy business).
Diagram of brake line locations on the ABS valve body in this thread (post.6): https://www.corvetteforum.com/forums...tor-valve.html
If nothing then you either have an internal blockage which a good back flush may correct or you may have a stuck valve for the RH front circuit. Its not common but does happen.
If you have a stuck valve you will not be able to pass any fluid through the unit in either direction as the sliding valve ensures the passages are completely cutoff. If this is the case you will need to replace the entire pump/modulator unit as they are not considered serviceable.
If you have good fluid flow at the caliper bleeder nipple then the ABS is unlikely to be the issue. Check for a frozen caliper piston or binding on the caliper sliders/pins.
As regards the pump activating randomly this suggests you have a control module issue. The pump should not run unless you have made a strong braking action enough to activate the ABS (pulsating action felt through the brake peddle). The dash ABS light will not come on as the unit considers its self to be working - albeit incorrectly.
The ABS moves the solenoid valves (one for each front wheel and just one for both back wheels) to stop further pressure to the skidding wheel and then releases the pressure to an accumulator chamber to release the brake.
The accumulator chamber only holds about 2cc of fluid so when the control module senses it is full it activates the pump to empty the accumulator and return the fluid into the master cylinder feed pipe. This all happens in in rapid succession causing the pedal to pulsate.
This is the only time the pump should run as it serves no other purpose.
Therefore the pump should only run under extreme braking. Since you say this occurs at stop signs I'm assuming you have an automatic where you are holding your foot on the brake pedal to stop creeping forward.
The control module receives a signal from the brake peddle stop light switch when you apply the brakes which activates the unit. This signal may be incorrectly activating the pump without the required signal from a full accumulator. However, there are also a number of other issues that could be the problem.
Unfortunately it becomes a job for a brake shop or auto electrician to isolate the issue at this point as you ideally need a J-35890 ABS tester which unfortunately are not common anymore.
However, after paying for this diagnosis chances are all that can be done is the replacing of pump/valve body and or control module.
If you can find a reasonably priced control module that you know is in good working order then that would be my initial recommendation subject to whether the ABS is blocked (and clearable) or has a stuck valve.
If its a stuck valve then you would most likely be better off financially purchasing a complete working unit with modulator valve body(which includes the pump) and control module all from the same car.
Or of course, you could just delete the ABS as I mentioned above. It all comes down to time and dollars.
Last edited by VikingTrad3r; 12-12-2015 at 10:22 AM.
12-12-2015, 11:26 AM
#20
Racer
Thanks!