Doesn't seem like I have power brakes any more

[Cntrysthbst]

1992 Buick Park Avenue with ABS

Here's the work I did - I replaced the calipers and cylinders, the pads and shoes, and the rotors and drums all at the same time. I bleed every wheel in its right order several times. I have adjusted the rear brakes 3 times to allow break in and to just double check them because of the brake problem I'm having.

Here's whats wrong - Everything was fine till about 3 days afterwards. Then I push the brake to stop and it will go down 3/4 of the way and it really nose dives, it's like the back end just wants to fly up and as soon as I stop the back end meets the ground. If I pump them about 2 to 3 times before I need to really brake it brakes good. Now I'm feeling front rotor wharping, the hot spots. I almost never have time to pump the brakes before I stop. There are no leaks, fluids correct, brake light does not come on, and no abs codes. I have rebled the system 3 times and checked the adjustment on the back brakes with no luck.

What is my next step to fixing this? Is there any testing I can do that might pin point this problem? Thanks!

[HotZ28]

Just a couple of things that come to mind, the master cylinder and the rubber brake lines to the front calipers.

[Cntrysthbst]

Ok, how would I check the brake lines? or should I just replace them?

Can I replace all the rubber rings in the M/C or is it better to get a new one?

Thanks

[HotZ28]

The rubber brake lines usually fail from the inside and you can not see it, but the line will swell when pressure is applied, therefore, it requires more fluid to engage the caliper. It is better to replace the master cylinder and lines with new parts. Try the lines first, they are cheap compared to the master cylinder.

One more question, when you changed the brakes, did you compress the calipers without opening the bleeder valve? If so, you may have contaminates from the old calipers back up to the master cylinder. That could cause the seals to fail.

[Cntrysthbst]

No I did not open the bleeder valve. Yeap - another lesson learned! Does it blow the seals out of place or just eat them? Can you also recommend a specific M/C and brake lines? Don't want to put something in that fails in short time! How about the proportioning valves in the back, is there a check I can do on them? And last, could I have damaged the seals in the ABS unit with the contaminates? Thanks!

[Cntrysthbst]

Quick question, I have JM4, that's Teves Mk 4 right? If I did let the res. run dry alittle when I was bleeding, can I bleed the M/C just to make sure? Do I have to do any bleeding at the ABS unit, or can I just go to bleeding the lines after the M/C is bled? Thanks!

[Cntrysthbst]

Ok, bled the M/C, bled all brakes - rr, lr, fr, fl in that order. Did not pump to do this, had wife slowly push the petal each time, hope that is correct, and adjusted the rear brakes. Brakes seem better however it didn't fix the problem. They still go half way down before stopping. If I push the brakes and hold the petal down it slowly goes to the floor in about 10 seconds. Can I have a booster problem?

[HotZ28]

I hate to be the one to say it, but all indications point toward the master cylinder leaking by the piston seals. I would not worry about the ABS unless you have a code.

[Cntrysthbst]

Ok, Thanks! Will replace Master Cylinder.

Ya know I've wondered why, out of ALL the forums/threads I've read, why you weren't the Moderator. All Moderators have been knowledgeable and have done a good job! In my opinion though you are the best man for the job! Trustworthy, reliable, great communication, knowledge, and PATIENCE, are just a few great traits you offer everyone here! Thanks for all you've done, and put up with, and mostly good luck!

[HotZ28]

Rob, your kind words are greatly appreciated! Maybe in the role of a moderator, I can serve our fellow members even better. We have a very civilized group on the Buick forums and that always makes the job easier. Some of the other forums refer to the Buick forums as "old farts", and that may be true in many cases.


We have another very qualified AF member by the name of bnaylor (Bob) who recently joined the Buick moderators team and describes himself as an “Old Hot Rodder”, so I assume that qualifies him as an “old fart” also. I guess if the old farts fall flat on their face, we still have the younger and much respected "tman" as backup.

As always, it is our pleasure to provide a service to AF members!

[Cntrysthbst]

Replaced M/C. Pretty simple. Bled system. All is well! Thanks for all the help!

[HotZ28]

Another example of how persistence, patience and knowledge, all combine to provide success! By the way, are you keeping a log or file on all the parts you have replaced on that PA. It would be interesting to post everything you have done at some point.
Good job Rob, and thanks for the feedback.

[Cntrysthbst]

Yeap! The file is gettin thick! Not proud of it but just can't let go of it. Yet!