Lack of fluid out of the calipers when bleeding the brakes?
12-09-2013, 04:45 PM
#1
Melting Slicks
Thread Starter
Lack of fluid out of the calipers when bleeding the brakes?
Hey guys. My master had a leak out of the side where the rod from the power brake booster pushes it so I replaced it. Before reinstall, I did bench bleed it in a vise.
My issue now is that I'm not able to get a firm pedal and I'm not seeing nearly as much fluid come out of the calipers as expected. I have speed bleeders installed on all 4 corners. According to the speed bleeders propaganda, it's not supposed to take many pumps of the pedal to bleed the brakes.
What I'm finding is that with the plastic tubing connected to the bleed screw, only a few inches of tubing will be full with fluid after pushing the brakes a 100 times or so. Even if exaggerated, it's not nearly what the literature claims and it's not getting me anywhere; it would take a 1000 pumps to clear one corner!
It feels like their is pedal pressure pretty close to when I start pushing the brake pedal but is there a possiblity that I may have to adjust the rod on the power brake booster outward?
One thing that I tried yesterday was going back to a standard bleeding screw that was open and had my wife push the pedal while I visually checked to see if any fluid was coming out into the tube. We tried about 5 or 6 times but I saw no fluid.
What gives? Do I need to bleed the abs unit or should that not have much to do with this?
My issue now is that I'm not able to get a firm pedal and I'm not seeing nearly as much fluid come out of the calipers as expected. I have speed bleeders installed on all 4 corners. According to the speed bleeders propaganda, it's not supposed to take many pumps of the pedal to bleed the brakes.
What I'm finding is that with the plastic tubing connected to the bleed screw, only a few inches of tubing will be full with fluid after pushing the brakes a 100 times or so. Even if exaggerated, it's not nearly what the literature claims and it's not getting me anywhere; it would take a 1000 pumps to clear one corner!
It feels like their is pedal pressure pretty close to when I start pushing the brake pedal but is there a possiblity that I may have to adjust the rod on the power brake booster outward?
One thing that I tried yesterday was going back to a standard bleeding screw that was open and had my wife push the pedal while I visually checked to see if any fluid was coming out into the tube. We tried about 5 or 6 times but I saw no fluid.
What gives? Do I need to bleed the abs unit or should that not have much to do with this?
12-09-2013, 05:42 PM
#2
Team Owner
Pro Mechanic
I question your bleeding of the master cylinder.
If you bled the master correctly, and haven't let air into it since (by running the reservoir down), then even w/o speed bleeders, you should have been able to open all the bleeders, pump the brake a couple times to move the air through the system, then let the calipers fill and start dripping for a minute or two...and you're done.
I'd go back, re-bleed the master (on the car), and proceed from there.
If you bled the master correctly, and haven't let air into it since (by running the reservoir down), then even w/o speed bleeders, you should have been able to open all the bleeders, pump the brake a couple times to move the air through the system, then let the calipers fill and start dripping for a minute or two...and you're done.
I'd go back, re-bleed the master (on the car), and proceed from there.
12-09-2013, 07:19 PM
#3
Melting Slicks
Member Since: Sep 2008
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"but is there a possibility that I may have to adjust the rod on the power brake booster outward?"
Might have a situation where the push rod is already 2 far out not allowing the MC piston to return fully. If the MC piston does not return fully the MC piston bore will not refill with fluid resulting in the exact problem you are experiencing.
Easy way to check, loosen the master & slip a couple of alignment shims between the master & booster. If you get fluid from the calipers the booster push rod needs to be shortened.
Suggest waiting at least 2-3 seconds between pedal pumps to give the master time to refill.
Good luck
Might have a situation where the push rod is already 2 far out not allowing the MC piston to return fully. If the MC piston does not return fully the MC piston bore will not refill with fluid resulting in the exact problem you are experiencing.
Easy way to check, loosen the master & slip a couple of alignment shims between the master & booster. If you get fluid from the calipers the booster push rod needs to be shortened.
Suggest waiting at least 2-3 seconds between pedal pumps to give the master time to refill.
Good luck
12-09-2013, 11:49 PM
#4
Melting Slicks
Thread Starter
thanks for the input guys. Here's some more info and a summary of what I tried today.
Previously the pedal went down a bit before starting to engage the brakes so I moved the rod in the brake booster slightly outward by rotating the end counter clockwise. So churchkey, you may be onto something here.
Tonight I undid the brake lines and connected the fittings and tubing to bleed the master again. I got fluid and plenty of it out of the port closest to the driver's seat(the front). Surprisingly, I got no fluid out of the forward port(the rear line). I would pump the break, hold it for a few seconds and then let it out. I would wait a few seconds and then repete. I did this about 30 times and I could see the bubbles in the line getting smaller.
When I checked the forward tube, there was still no fluid in the clear tubing. Not even a drop.
One thing I did notice is when I was hooking up the fittings with the clear tubing, I did get some fluid dripping out of the one closer to the driver's seat. There was no fluid out of the forward one.
Anyhow, I had my wife come out and pump it some more but first I loosened up the bolts holding the master to the booster to try to offset the rod adjustment I did. I started so that there was maybe an 1/8" gap between the two components. We pumped it about 25 more times and still nothing. Finally I did it so that there was about 3/16 or 1/4" gap and pumped it some more. Still nothing. The rear line is still 100% dry with no fluid coming out of the master.
Thoughts? Originally when I was bench bleeding the master, I did see a little fluid out of the rear port. Now I'm not seeing anything.
Previously the pedal went down a bit before starting to engage the brakes so I moved the rod in the brake booster slightly outward by rotating the end counter clockwise. So churchkey, you may be onto something here.
Tonight I undid the brake lines and connected the fittings and tubing to bleed the master again. I got fluid and plenty of it out of the port closest to the driver's seat(the front). Surprisingly, I got no fluid out of the forward port(the rear line). I would pump the break, hold it for a few seconds and then let it out. I would wait a few seconds and then repete. I did this about 30 times and I could see the bubbles in the line getting smaller.
When I checked the forward tube, there was still no fluid in the clear tubing. Not even a drop.
One thing I did notice is when I was hooking up the fittings with the clear tubing, I did get some fluid dripping out of the one closer to the driver's seat. There was no fluid out of the forward one.
Anyhow, I had my wife come out and pump it some more but first I loosened up the bolts holding the master to the booster to try to offset the rod adjustment I did. I started so that there was maybe an 1/8" gap between the two components. We pumped it about 25 more times and still nothing. Finally I did it so that there was about 3/16 or 1/4" gap and pumped it some more. Still nothing. The rear line is still 100% dry with no fluid coming out of the master.
Thoughts? Originally when I was bench bleeding the master, I did see a little fluid out of the rear port. Now I'm not seeing anything.
12-10-2013, 12:00 AM
#5
Team Owner
Pro Mechanic
"but is there a possibility that I may have to adjust the rod on the power brake booster outward?"
Might have a situation where the push rod is already 2 far out not allowing the MC piston to return fully. If the MC piston does not return fully the MC piston bore will not refill with fluid resulting in the exact problem you are experiencing.
Easy way to check, loosen the master & slip a couple of alignment shims between the master & booster. If you get fluid from the calipers the booster push rod needs to be shortened.
Suggest waiting at least 2-3 seconds between pedal pumps to give the master time to refill.
Good luck
Might have a situation where the push rod is already 2 far out not allowing the MC piston to return fully. If the MC piston does not return fully the MC piston bore will not refill with fluid resulting in the exact problem you are experiencing.
Easy way to check, loosen the master & slip a couple of alignment shims between the master & booster. If you get fluid from the calipers the booster push rod needs to be shortened.
Suggest waiting at least 2-3 seconds between pedal pumps to give the master time to refill.
Good luck
12-10-2013, 10:23 AM
#7
Melting Slicks
Member Since: Sep 2008
Location: Cherokee National Forest TN
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Agree or the prop valve in the master has been triggered & is off center. If there is a brake warning switch in the master remove it & look in the bore. The prop valve piston has a groove machined into it, the groove should be centered in the bore.
12-10-2013, 05:10 PM
#9
Melting Slicks
One thing I question when you push the brake to the floor are you then covering the port with your finger before letting up on the brake? If not every time you pump the brake you are letting air in and you will not get anywhere. Also are you doing one wheel at a time? If I am in no hurry I gravedy bleed brakes. top off the system open one bleeder and let it run till the resovier is almost empty. Top off then do another and repete till you have done them all...I have also found this is a very good way to see if you have a hose colasping if you are not getting flow out of the bleeder chances are you have a line colasping.
12-10-2013, 06:04 PM
#10
Melting Slicks
Thread Starter
Are you speaking of bleeding the master or at the wheels? For the master, I had the plastic lines from the discharge ports back into the fluid tank on top of the master. So, when I let off the pedal, it would suck in fluid and not air.
For the wheels, I have speed bleeders on there that act like a one way check valve (supposedly!).
I'm open to any suggestions or tips though because this is only my 2nd time doing this.
For the wheels, I have speed bleeders on there that act like a one way check valve (supposedly!).
I'm open to any suggestions or tips though because this is only my 2nd time doing this.
12-10-2013, 07:15 PM
#11
Melting Slicks
they way you did the master cyc is right, I am not a fan of spped bleeders but that is just me. I always belled the master the way you did. But if air some how got into the system if I have the time I perfer to gravalty bleed like I said. I have neverhad a problem with air this way plus you are fushing the system at the same time
12-11-2013, 10:16 PM
#12
Melting Slicks
Thread Starter
hi guys. I made some great progress with the assistance of hot rod roy who lives in the area. He knows a heck of a lot about the corvette braking system.
We found that I am missing the pressure sensor on the bottom of the master causing fluid and pressure to leak out of there.
I went back to autozone and my core did not have the sensor so I must have made this mistake when I swapped it years ago.
I went to the dealer and they want $62 for the master cylinder pressure sensor. I don't know that I can get it anywhere else, but does anyone have any suggestions? I tried autozone and pep boys so far. The other option is just plugging it and see what happens. It's been not in use for some time so what could possibly happen?.... (chuckling under my breath)
Here's a photo of the bottom of the master. The port in question is on the top side of the piece.
We found that I am missing the pressure sensor on the bottom of the master causing fluid and pressure to leak out of there.
I went back to autozone and my core did not have the sensor so I must have made this mistake when I swapped it years ago.
I went to the dealer and they want $62 for the master cylinder pressure sensor. I don't know that I can get it anywhere else, but does anyone have any suggestions? I tried autozone and pep boys so far. The other option is just plugging it and see what happens. It's been not in use for some time so what could possibly happen?.... (chuckling under my breath)
Here's a photo of the bottom of the master. The port in question is on the top side of the piece.
Last edited by qwiketz; 12-11-2013 at 10:24 PM.
12-12-2013, 03:04 AM
#14
Race Director
The pressure balance switch port should be dry. If you have brake fluid there then you have an internal leak in the master cylinder.
The part number for the switch is 10074131. It was used on all Corvettes from 1984 through 1995. '96s don't have one.
Try this one:
The part number for the switch is 10074131. It was used on all Corvettes from 1984 through 1995. '96s don't have one.
Try this one:
