Brake Experts - Help!!

[scottso]

My 2002 Venture has a very strange brake issue. When you come to a stop and "feather" the brake pedal (small pumps not letting it completely rise) - the pedal sinks to the floor. Several applications of this feathering and it is close to the floor. If I stop and hold pressure on the pedal - it does NOT sink at all - likewise if I repeatedly step on the pedal using full cylces letting the pedal rise all the way before pressing it again. This tells me it is not a master cylinder issue.
The shop I took it to found no problems or error codes in diagnostics and said that the ABS unit may have a sticking valve. They did a fluid vac hoping it might "free up" whatever "might" be sticking and it is about 50% better. They are telling me the ABS unit is $1300 from GM! Has anyone had this problem?? $1300 is insane!!

[AJT1961]

If I understand you correctly, it sounds pretty much normal to me. It's not like the old brake systems where you bled it and you could get yourself a rock hard pedal. If you work the pedal as you describe, you can if fact get it all the way to the floor. Mine was like that. If my wife was home now, I'd go out and try it on her Uplander which should be same system. (I'll check when she gets home this evening). Perhaps I'm misunderstanding you though. How does it feel in normal driving? "Mushy" is kind of normal, but does it ever reach the floor in normal driving without the little pumps on the pedal? If you do need an ABS unit though (which I doubt), I'd check the junkyards first -- $1300 is simply obscene.

[scottso]

The pedal is not "mushy" at all. Hit the brakes and they feel fine. But apply them, then release them partially (not letting the pedal return all the way up), then apply again - every repeat of this procedure lowers the pedal closer to the floor for the brakes to grab (maybe 4-5 times before you are way down near the floor). It's a feeling I have never had in any other car I've had. I certainly can't do it in my camaro. With this condition - if you are in slow moving traffic where you need to hold/release partial pedal - you need to keep "resetting" it by doing a full release to get the high pedal back.
It is my wife's daily driver (not mine) - and she said it did not feel normal either. The shop said the same.

[AJT1961]

So it keeps sinking at a stoplight all by itself to the point that you need to release the pedal and reapply the brakes to actually keep it from rolling?

[scottso]

Originally Posted by AJT1961

So it keeps sinking at a stoplight all by itself to the point that you need to release the pedal and reapply the brakes to actually keep it from rolling?

Nope. If I hold firm pressure - it will stay put - that's what confuses me. It's only the PARTIAL (not full) release and re-application that causes it to sink.

[AJT1961]

Sounds normal to me. My 99 did the same thing -- I don't know why. Reminds me of the old joke, "Doctor, it hurts when I do this...." Well, you know the rest.

[534BC]

This sure does not sound normal to me.

[Huney1]

Ours is a Y2K with 63K mi on it always adult driven. I tried pumping it fast and it went down some but never went to the floor. If I sit and hold steady pressure on the pedal it stays right there and doesn't sink. Your problem would be typical of a master cylinder leaking, but you don't have regular brakes and I know from zilch about ABS brakes. As long as you're not losing brake fluid and the braking characteristicsw are OK then I wouldn't worry about it. If you have doubts pay Mr Goodwrench a visit.

[scottso]

OK - the condition is NOT normal. Here is the deal. I had peeked at the wear indicators (through the wheel) on the front brakes and they looked fine. I did a visual by pulling a rear wheel and they were fine - all of this before visiting the shop. They pulled the front wheels and found the inner pads almost gone, and rears out of adjustment. That taken care of, they did a fluid vac on the system. When I got the car back it was better, but not 100%. They said to use it for a few days and come back if the problem was not better. As of today - the problem is gone, it is a normal pedal. Call it too much travel because of the wear/out of adjustment, a sticking ABS valve, or maybe moisture in the fluid - but it is now a normal pedal.

[scottso]

It's back. The past several days has seen the condition return. It was completely gone and now it is back. I guess Mr. Goodwrench is in my future after all. It ticks me off because there are no error codes on the dash or retrieved by the shop where it had the brake job done. But it can be dangerous if you are feathering the pedal coming to a stop - it can really catch you by surprise when the pedal drops.

[534BC]

I don't know much about abs, The problem sounds like it is the cup in the master cylinder shrinking (not sealing unless there's pressure)

I can't gues how much a master cyclinder is,,,

[Huney1]

"I don't know how much a master cylinder is." $84.36
http://replacement.autopartswarehous...inder&dp=false Try PEP Boys and some of the big parts stoeres and you might find it a bit cheaper and find out about rebuilt ones. I think theres a kit you can buy to rebuild yours, but I'd let a good brake mechanic do it.

"They are telling me the ABS unit is $1300 from GM! Has anyone had this problem?? $1300 is insane!!"

WOW, that is a lot of pepperoinis! I'm not savvy on ABS units but check salvage yards and auto parts stores. We have a decent independent repair shop here and if I need something fixed I go to them and ask the most economical and safest way to go. However, when you're dealing with something that could very well save your life and the lives of your family, I wouldn't fool around repairing brakes and I'd have it done right.

[cjstew4]

One thing I would do is to bleed the brakes properly per the repair manual. There is a certain sequence that worked for me that is described in the repair manual that I do not have on me right now. Also, check your slave cyclinders on the rear wheels, since mine was leaking on the inside, not detected by the mechanic, and was causing both my ABS and TCS lights to come on.

[DRW1000]

I am no expert by any means but I don't believe that the ABS sysytem can (or should) cause the problem you described. I would consider the master cylinder to be the focus of your troubleshooting.

[Huney1]

I agree with DRW1000. Thee has to be several shops in your town that does brakes, and brakes are a common repair item. I'd get several different opinions from several shops and surely one of the mechanics can put the finger on exactly what is wrong. If you aren't losing fluid then the problem is internal and all you need do is find what's leaking and replace it. If the wheel cylinders leak they will show a tell tale external wetness indicating leaking. The master cylinder can leak (fluid pressure) internally and not get wet outside but I don't know if the ABS unit itself can leak internally. Thats the box with all the brake fluid lines coming out of it like an Octpus.

I still say if you ask enough 'knowledgable' people someone will have an answer. How about Midas or a shop that specializes in brakes? I'd go to every shop in town including Ford, Chrysler and the imports and describe your probloem to the service writer and ask him to go ask the brake man if he knows what's causing your problem. "Seek and Ye shall find . . . . "