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I am working on an 88 with a 300i6 and a manual trans and having brake pedal issues that I think I have multiplied.
About a month ago I noticed pretty text book air-in-the-line pedal drop. I attempted a bleed job, the first time I forgot to do the ABS unit in the frame, so I went back and bled a second time in the correct order: P Rear, D Rear, ABS, P Front, D Front. I got all bubbles out and my brake pedal has less drop than it did before but still some. The more concerning issue is that now my front brakes want to lock up on a moderately hard press. I also now have pulsation when applying pressure on a long downhill for example.
The continued pedal drop indicates that I may just need to bleed again but before spending another $20 on fluid flushing I'd like to see if anybody else has had a similar front brake locking issue. I am not getting any lights on the dash but am worried that the entire issue might be tied up in a bad sensor/computer issue at the ABS unit or somewhere else related. If anybody has any advice or tests I can do to rule things out that'd be much appreciated.
I am able to stop the truck like I usually did, downshifting with light brake input pressure, so I assume my rears are still working. Is there a way I can verify that the rears are doing something? Temperature test or a visual inspection?
I am able to stop the truck like I usually did, downshifting with light brake input pressure, so I assume my rears are still working. Is there a way I can verify that the rears are doing something? Temperature test or a visual inspection?
My issues were almost identical to yours. Ended up being the brake booster. I also installed a new MC and all is well. Investigate booster symptoms and see if anything coincide with your symptoms. Sandy
About a month ago I noticed pretty text book air-in-the-line pedal drop.....The more concerning issue is that now my front brakes want to lock up on a moderately hard press. I also now have pulsation when applying pressure on a long downhill for example.
The continued pedal drop indicates that I may just need to bleed again but before spending another $20 on fluid flushing I'd like to see if anybody else has had a similar front brake locking issue.
Pedal continuing to drop when stopped at a traffic light for example is usually caused by an internal leak in the master cylinder.
Thanks for the suggestions, glad I'm not the only one who's had these issues. Did some booster diagnostics (pedal pressure tests with engine on and off), checked the check valve and it all seems to be working fine. I also have corrosion on the front of the booster that I previously thought was part of the firewall/clutch pedal leak problem these trucks have, but could be an explanation of the brake issue.
Could the issue be as simple as a new gasket or is it better to just replace the entire master?
I also noticed another bleeder screw along the lines that I didn't see before. I bled the unit further back in the frame but never this piece:
Could either of these things be causing the anti-lock to quit working?
Thanks for the suggestions, glad I'm not the only one who's had these issues. Did some booster diagnostics (pedal pressure tests with engine on and off), checked the check valve and it all seems to be working fine. I also have corrosion on the front of the booster that I previously thought was part of the firewall/clutch pedal leak problem these trucks have, but could be an explanation of the brake issue.
Could the issue be as simple as a new gasket or is it better to just replace the entire master?
I also noticed another bleeder screw along the lines that I didn't see before. I bled the unit further back in the frame but never this piece:
Could either of these things be causing the anti-lock to quit working?
The brake booster has a diaphragm and they will tear. When that happens fluid goes into the booster and that's the leakage you see. the booster appears to be the problem.
Based on that photo I would say its time. Your Master Cylinder is leaking into your Brake booster causing issues. I just fixed this on the F350 at the beginning of the year. Brakes felt much better when I was done.
I attempted a bleed job, the first time I forgot to do the ABS unit in the frame, so I went back and bled a second time in the correct order: P Rear, D Rear, ABS, P Front, D Front. .
Originally Posted by HLavery
Thanks for the suggestions, glad I'm not the only one who's had these issues. Did some booster diagnostics (pedal pressure tests with engine on and off), checked the check valve and it all seems to be working fine. I also have corrosion on the front of the booster that I previously thought was part of the firewall/clutch pedal leak problem these trucks have, but could be an explanation of the brake issue.
Could the issue be as simple as a new gasket or is it better to just replace the entire master?
I also noticed another bleeder screw along the lines that I didn't see before. I bled the unit further back in the frame but never this piece:
Could either of these things be causing the anti-lock to quit working?
Um... That is the RABS module which begs the question: What ABS did you bleed in the first post?
There is no gasket to replace between the master cylinder and the booster. The master cylinder is leaking and either needs to be rebuilt or replaced.
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