I was bench bleeding my master cylinder when.....
04-16-2019, 10:32 PM
#1
Instructor
Thread Starter
I was bench bleeding my master cylinder when.....
hello again and thanks to all that have responded to previous posts/questions.
The fact that i am in the process of bleeding the brake system - means the brakes are back together as well as the suspension!!!
I would post pictures - but my phone and computer are not talking well together lately.
As the title states, I was bench bleeding my master cylinder for my brakes.
The front reservoir bled like normal, but the rear reservoir seemed not to be having the flow as in the front.
Now I am not used to having the proportioning valve built into the master cylinder.
Please correct me if i am wrong, since the output of the master cylinder goes thru the proportioning valve will the output flow be less than the front?
Is this normal or do i need a new master cylinder???
The fact that i am in the process of bleeding the brake system - means the brakes are back together as well as the suspension!!!
I would post pictures - but my phone and computer are not talking well together lately.
As the title states, I was bench bleeding my master cylinder for my brakes.
The front reservoir bled like normal, but the rear reservoir seemed not to be having the flow as in the front.
Now I am not used to having the proportioning valve built into the master cylinder.
Please correct me if i am wrong, since the output of the master cylinder goes thru the proportioning valve will the output flow be less than the front?
Is this normal or do i need a new master cylinder???
04-17-2019, 08:11 AM
#2
Safety Car
It would help if you listed some facts on your car like the year. Starting with 86, there's a ABS pump in a well behind the seat. I have read where a couple of people either had internal rust issues in the pump or something got into the pump and plugged up some of the passages. If you're not getting any flow to the rear calipers it could be worth checking if you have flow going to the abs pump and not anything coming out.
I know there was a unit used to cycle the pump while bleeding the brakes when it was done by the dealership but unless you can find one used I'm not sure if they're available any more.
I did find some info in an old thread relating to this subject, here's that info:
I know there was a unit used to cycle the pump while bleeding the brakes when it was done by the dealership but unless you can find one used I'm not sure if they're available any more.
I did find some info in an old thread relating to this subject, here's that info:
Possible substitute for Kent Moore J-35890?After doing some reading about the Bosch ABS 2 system it seems the basic systems are the same with the only thing different being resistance values of wheel speed sensors. I remember a older post on this forum stating that different late model Porche and Cadillac wheel sensors working on earlier C4's and a Google search brought up a gentleman who had success analyzing his Corvette ABS with a old LED 2 tool from Porsche. I decided to take a small gamble and purchace a OTC Mitusubishi ABS Tester MB991131-02. It looks identical to the Kent Moore tool down to the 35 pin connector. I figure at best it works completely or enough to test everything but the wheel sensors and if not I'm not out that much cash. Maybe this will be a lower cost alternative to the Kent Moore tool. I'll attach some pics of bothAttached Images[img]mhtml:file:///F:/Corvette/Tech_Articles/Possible%20substitute%20for%20Kent%20Moo re%20J-35890%20-%20CorvetteForum%20-%20Chevrolet%20Corvette%20Forum%20Discus sion.mht!https://www.corvetteforum.com/forums/attachments/c4-tech-performance/47920342d1443918809-possible-substitute-for-kent-moore-j-35890-_35.jpg[/img]
Last edited by hcbph; 04-17-2019 at 08:15 AM.
04-17-2019, 11:35 AM
#3
Melting Slicks
It would help if you listed some facts on your car like the year. Starting with 86, there's a ABS pump in a well behind the seat. I have read where a couple of people either had internal rust issues in the pump or something got into the pump and plugged up some of the passages. If you're not getting any flow to the rear calipers it could be worth checking if you have flow going to the abs pump and not anything coming out.
I know there was a unit used to cycle the pump while bleeding the brakes when it was done by the dealership but unless you can find one used I'm not sure if they're available any more.
I did find some info in an old thread relating to this subject, here's that info:
I know there was a unit used to cycle the pump while bleeding the brakes when it was done by the dealership but unless you can find one used I'm not sure if they're available any more.
I did find some info in an old thread relating to this subject, here's that info:
Possible substitute for Kent Moore J-35890?After doing some reading about the Bosch ABS 2 system it seems the basic systems are the same with the only thing different being resistance values of wheel speed sensors. I remember a older post on this forum stating that different late model Porche and Cadillac wheel sensors working on earlier C4's and a Google search brought up a gentleman who had success analyzing his Corvette ABS with a old LED 2 tool from Porsche. I decided to take a small gamble and purchace a OTC Mitusubishi ABS Tester MB991131-02. It looks identical to the Kent Moore tool down to the 35 pin connector. I figure at best it works completely or enough to test everything but the wheel sensors and if not I'm not out that much cash. Maybe this will be a lower cost alternative to the Kent Moore tool. I'll attach some pics of bothAttached Images[img]mhtml:file:///F:/Corvette/Tech_Articles/Possible%20substitute%20for%20Kent%20Moo re%20J-35890%20-%20CorvetteForum%20-%20Chevrolet%20Corvette%20Forum%20Discus sion.mht!https://www.corvetteforum.com/forums...-35890-_35.jpg
Last edited by 3D-Aircrew; 04-17-2019 at 11:35 AM.
04-17-2019, 07:32 PM
#4
Instructor
Thread Starter
There is no blockage in the ABS unit behind the driver's seat, because i removed and bypassed it.
It was bad,blocked and flooded. Yes flooded.
A leaky convertible top and an ABS module sitting in the equivalent of a bucket - is not a good idea - nothing good will come from it.
I was asking about the master cylinder after it has been removed from the car.
I apologize for the confusion
It was bad,blocked and flooded. Yes flooded.
A leaky convertible top and an ABS module sitting in the equivalent of a bucket - is not a good idea - nothing good will come from it.
I was asking about the master cylinder after it has been removed from the car.
I apologize for the confusion
04-17-2019, 09:23 PM
#5
Drifting
The rear brakes need considerably less fluid volume than the fronts. There is a lot of physics to it, but the short answer is it keeps
the rears from locking up and causing a spin.
the rears from locking up and causing a spin.
04-17-2019, 10:24 PM
#6
Instructor
Thread Starter
I understand the average car has 70% of its braking performed by the front brakes.
I also understand why the brake lines and calipers are smaller in the rear compared to the front.
I also understand the dynamics of applied stopping force necessary to keep a vehicle controllable in a variety of driving situations.
yes, in a traditional front disc and rear drum brake system the rear brakes had wheel cylinders, which took less volume than a caliper on a disc brake.
With that said - a 4 wheel disc would take more fluid than a drum/disc system. there is a difference between volume and pressure.
This i understand as well.
I have discussed this with three local mechanics as well.
When bench bleeding a master cylinder that has been removed from a vehicle.
With the naked eye you will not notice the difference in flow or volume from front or rear reservoirs.
The master cylinder i have has two separate reservoirs, not the one reservoir that is diagonally split to the rear of the master cylinder.
I have ordered a new master cylinder today - Rock Auto $119 with reservoirs
I deleted the ABS module due to the lack of available parts and the cost - if you found them working.
I searched this forum and followed others have done to their Corvettes - it was spot on.
My Corvette is a 130,000 mile convertible that has been creatively ignored or creatively maintained for years prior to my ownership.
Once I get it safe to drive on the road - this will become a daily driver for me.
I also understand why the brake lines and calipers are smaller in the rear compared to the front.
I also understand the dynamics of applied stopping force necessary to keep a vehicle controllable in a variety of driving situations.
yes, in a traditional front disc and rear drum brake system the rear brakes had wheel cylinders, which took less volume than a caliper on a disc brake.
With that said - a 4 wheel disc would take more fluid than a drum/disc system. there is a difference between volume and pressure.
This i understand as well.
I have discussed this with three local mechanics as well.
When bench bleeding a master cylinder that has been removed from a vehicle.
With the naked eye you will not notice the difference in flow or volume from front or rear reservoirs.
The master cylinder i have has two separate reservoirs, not the one reservoir that is diagonally split to the rear of the master cylinder.
I have ordered a new master cylinder today - Rock Auto $119 with reservoirs
I deleted the ABS module due to the lack of available parts and the cost - if you found them working.
I searched this forum and followed others have done to their Corvettes - it was spot on.
My Corvette is a 130,000 mile convertible that has been creatively ignored or creatively maintained for years prior to my ownership.
Once I get it safe to drive on the road - this will become a daily driver for me.
04-17-2019, 11:40 PM
#7
Drifting
I recently replaced the MC on my '86. I was somewhat surprised at how little fluid went to the rear when i bench bled it
and when i power bled the system to replace the fluid in the entire system. I really wasn't questioning your knowledge
of brake systems. I was and am confirming what you observed as normal. I hope you get it on the road soon.
and when i power bled the system to replace the fluid in the entire system. I really wasn't questioning your knowledge
of brake systems. I was and am confirming what you observed as normal. I hope you get it on the road soon.
04-21-2019, 10:33 AM
#8
Advanced
I recently replaced my master cylinder on my '91.
I checked the old one and it was much like yours, back had considerable less fluid when bench bleeding. It was more than a dribble but certainly not a strong flow.
The replacement *seemed* better than the old one, but I think it was also less than the front. Brakes are much better now than before.
Dale
I checked the old one and it was much like yours, back had considerable less fluid when bench bleeding. It was more than a dribble but certainly not a strong flow.
The replacement *seemed* better than the old one, but I think it was also less than the front. Brakes are much better now than before.
Dale
Last edited by zzpw3x; 04-21-2019 at 10:33 AM.