OK, so I have had this problem for a LONG time and I can't figure it out.

Problem:

Driving along and hit the brakes, a little or a lot, doesn't matter. And they don't let go after I take my foot off the pedal. Just keep grabbing at whatever the max pressure was that I applied. Finally they let go after a couple seconds. Then if I try to make the problem happen again on demand. I can't. It is totally random.

Motor only makes 8" vacuum. So of course susspeced this. I have a vacuum canister. And have been on the highway where I can have 20" of vacuum and had the happen. Then I have also gone 5 MPH with litte vacuum and slammed the brakes over and over using up all the vacuum and the problem doesn't happen no matter what.

Replaced:

EVERYTHING. Booster, lines, fluid, upgraded to C5 calipers, new rotors, prop. valve and all. master cylinder, pads, EVERYTHING.

Problem has been there before all the stuff was replaced and is still there.

Leads me to believe that I need more vacuum. But if that is the case, then why does it still happen on the highway!?

i am lost. If anyone can give me a 100% clear reason for the problem and it fixes it I swear I will send them $50.

Only thing I havn't tried is buying a vacuum pump. I don't want to toss the $200 at the problem if I don't have to.

I pretty much am looking for any ideas as to why this problem is happening. I can't find anyone else that has this issue.

Thanks for any help!

 

One of your brake lines has an internal tear and it is acting as a flapper valve. This can happen with new lines. remove your flexible lines and try blowing through them in both directions after you have cleaned them to find the culprit. I have witnessesed this twice.

I would look here first.

 

my brakes were all new when i bought the car and i had a problem like this but mine was only one brake doing that. i had a colapsed brake line and it did that all randomly then they completly locked up on me one day and i got really pissed so just throwing that out there.

 

I'll third the collapsed flex line. I went through this with a friend's car. Line looked perfect outside but had exactly the symptoms you describe. We were about to replace the proportioning block and had pulled the flex lines to get the job started when we saw the problem.

 

I'm taking a break from my master cylinder for a minute and decided to look on here. I have a similar problem and am gonna be pissed if the line is my problem too. I've already replaced the pads, calipers, and booster. After I get done with the master cylinder I'll see if it's fixed. If not sounds like I'm getting new brake lines, just another excuse to get the stainless braided hoses I want, wife can't say no if the car "needs" it. Not that she would say no anyway, she's got more wrench time than on the T/A than I do.

 

I have new braided lines though. And I think I have swapped them twice. I can't remember now.

I have stainless lines too.

Thanks guys, I will take each line out and try to blow though it. Gut feeling is that this will not be it, but if you guys say to try it I will.

I will report back in a week or two, when i finally get a chance to work on her.


Thanks.

 

Try bleeding the system again.

Sounds like a collapsed line, Try clamping each line 1 at a time starting at the rear. Clamp the line then press the brake, pedal should be hard if not could be the front lines & or booster. Clamp front lines 1 at a time to see wich line or booster. Less vacum will make your brakes soft & you'll have to pump to build pressure. Usually cars with a big cam needs a vacume resivor.


Also you may wanna check the rod that pushes on your booster & Brake pedal assembly maybe something could be binding it & locking up your brakes.

 

I am positive that it is not the rod. THe pedal moves back, I can feel it with my foot. I have vacuum canister already.

Like I said, I will check the lines again. Even though they are new. But like was said before apparently there can still be a problem with them.

 

Check to see if the lines are kinked or binding on something. Turn your wheels lock to lock to see if you have any binding issues.

 

Remember to mark the lines in the direction the fluid would travel before removing them.

And blow in both directions to determine if there is a difference.

 

will do.

I also checked for binding a long time ago. Then double checked. Def no binding.

 

Oh yea...

Do one at a time.

This way you may not have to remove all three.

 

Thats the plan. Hopefully it will be a front on so I don't have to bother getting under the car. But oh well, we will see.

 

I finished my master cylinder the other day and got nothing so I ordered some new Earl's Hyperflex lines. Well I'll be damned if that didn't solve my whole problem. I was just trying to get the brakes fixed so I could drive the car before I go back to Iraq, now that I've spent all this money on the brakes I'm getting ready for an upgrade. Good luck finding out your problem. Really sucks when one of our cars is down for something like this.

 

yeah, I have still been driving it around cuz the problem only happens every so often.

I am already on my second set of stainless lines, ugh...

 

everyone is talking about the rubber lines, but what if the metal line has a kink somewhere in the system. it might be worth some inspection if the old lines have colapsed from rust or any new ones were bent upon installation.

 

Just chiming in here to re-confirm that collapsed brake lines are very frustrating to figure out. I had the same problem (with the addition of a serious pull when applying the brakes) and after replacing everything else first, it was the dang rubber lines. I have never, in 20+ years of building cars, had a this type of problem with rubber lines. Yea I've had lines burst before, but not emplode on themselves. Now I know whenever having apply/release problems with 3rd gen brakes, replace the rubber lines first!!!

 

I am on my 2nd set of braided lines though!

 

I might have missed it, but I will ask if you have rear drums and not rear disc?

Your rear brake shoe liners can be hanging up and locking in an out of tolerance drum- in other words, it is expanding beyond tolerance ranges and hanging up occationally.

 

Fronts are C5 Z06 with drilled/sloted and zinc washed rotors.
Rears are stock PBR disks that came on 91s the same that are on the 1LE cars.

All new stainless lines (exept where the line lock was installed, that is steel line). 2nd set of braided lines all around, even the little bits that go into the rear calipers from the hard lines on the Moser 12 bolt.

New master, Bench bled.

New booster.

Motor makes low vacuum, but this is not the problem, as I can get off the highway and have over 20" in the resivoir and it will still happen and I can sit in a parking lot and pump and pump and pump, use up all the vacuum and the pedal gets hard, but the sticking problem doesn't happen, then RANDOMLY, as I drive away, with vacuum or not, stiiiiiiick ------ let go.... UGH!!!!

 

Have you been able to issolate which calipers are hanging up. Mean is it an individual wheel i.e. LF, RF, LR, or RR..... or maybe it is both fronts, or both rears, or all of them together?

My thoughts are you have some residual debris inside maybe even a hard line that needs to be bleed though. It could be sitting right at a fitting flare and hanging up holding residual pressure when the pedal is released.

You are going to have to check out each part of the system individually.

I WOULD START... by jacking all 4 off the ground and having someone apply the brake pedal slightly as you check each indivdual tire rotation to see if you can pinpoint a culprit wheel that does not release as consistantly as the other 3.

 

can you tell if it is just one brake holding or if it is all of them, that would help you narrow your search. if it is all the brakes you would be looking at the pedal to master cylinder area that would affect all brakes, if it is only one wheel you could just trace that line to find the problem

 

All I know is that its both the fronts for sure.

Might be all 4 though. Hard to tell.

All I know is that there is no pull.

I was thinking about getting the system power bled as a first thing.

Any thoughts???

 

Until you posted it, I hadn't realized you had a line lock installed. Is there any chance that this isn't releasing sometimes? I was thinking about a collapsed hose, but it's uncommon to have two fronts go bad at the same time. A misbehaving line lock might have these symptoms.

 

I guess I could get another one, but it really feels like a waste of $.

I mean, with no voltage going to it, it is essentially a 3 way T-fitting.

MAYBE there is something stuck in the linelock that a pressure bleed will get out...

 

I would say Vette gator is on to something with the line lock.

The chance or thought of a line lock malfunctioning is illogical- but myseryous problems like this are illogical also. the senerio fits.

 

you are right, it does fit, but I still dunno how. It is crazy.

Only thing I can think of is what was stated b4. some bubble of debris caught in the line lock area.

I will pressure bleed and go from there.

 

I did not know you had a line lock.

remove it and see it the problem goes away.

I doubt you will "bleed your way past" this problem

 

At least remove it temporarily to see if it's the cause of your problem.

 

I hope one of my suggestions fixes your problem which sounds very dangerous to say the least. I am leaning towards #3 myself. Good Luck and I hope you resolve this issue soon.

1.) I didn't see you mention it but since you swapped to C5 calipers I would check to make sure you are using the proper brake fluid. i.e. DOT 5, DOT 3. I think those components may require DOT 5.

2.) I would check your brake line to header clearance if your brake lines off of the master cylinder are close to your headers this could be giving you some problems as well. Of course if you don't have headers please disregard this suggestion.

3.) Did you lubricate the slide pins or rests that the caliper self adjusts on. I am not familiar with C5 calipers but if the caliper is shifting (out of alignment) on its slide mechanism this could be the cause of the "sometimes" lock up.

 

I do have headers, but the lines are FAR away from them.

The C5 calipers don't have pins like the stockers do. But everything is well lubed.

The C5 brakes don't require any special fluid either.

I really do appreciate the help, but I am positive that it is not any of those 3 things. I have ruled them out already.

I will be getting the pressure bleed in a week or two,.

 

Any updates? I've been curious about this one.