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Very strange braking issue

1K views 7 replies 3 participants last post by  Tobolate 
#1 ·
Normally I just search for things like this but this issue is specific enough that I can't seem to find someone who is having a similar enough issue to diagnosis it. It's weird enough in fact that a local indie is also stumped. So here it goes.

One day after normal driving I started up the car to the store, I instantly knew something was wrong because at the first stop sign the brake pedal became extremely hard once it was pushed down half way, like it feels normal until you hit halfway down and becomes insanely hard like trying to push bricks. The car also pulled dramatically to the right, I'm talking pulled the wheel out of my hands.

Naturally I limped the car home to pull the wheel off and see why the caliper was apparently stuck. Sure enough, pads out and pedal pushed there was no piston movement on the caliper. Thinking it was stuck I tried to compress the pistons with a C-Clamp expecting harsh resistance however they slid back into the caliper like butter. Upon pushing the brake pedal there was still no outward movement on the pistons. Thinking possibly that there was some-how dirt or air in the system I attached my bleeder tool to the caliper and had a friend pump the pedal with the valve open only to find out that absolutely no fluid was coming out of the valve.

At this point I was pretty sure maybe the soft-line had internally collapsed, and went about replacing it, only to find that after changing it out, there was still no fluid coming from the bleeder.

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I took it to an indie because I was pretty stumped and he attempted force-bleeding the brakes, the other three calipers bled just fine however the driver front didn't bleed at all, even with the valve taken completely out of the caliper.

Carb cleaner has been sprayed on the area for the o-ring attaching the master cylinder to the booster as well as along the booster line and check valve. No hissing is present and the spray didn't effect the idle.

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The only thing I can think of at this point is that somehow the booster is messed up, but then i'm confused why only one caliper isn't working and also as to why the pedal feels vacuum assisted until its halfway down. That or the Hard-line is somehow clogged but I don't even know how that would happen.

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TL;DR:

My brake pedal feels hard halfway down and one caliper isn't working. Things done:

-Caliper compressed and inspected
-Soft-line replaced
-Force bled
-Vacuum tested

If anyone has any ideas or insight that would be great I'm pretty confused on this one :confused:.
 
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#3 ·
I will double check that tomorrow (Rear passenger) but when it was at the shop and we force bled the brakes we checked all calipers to make sure the bleed went well and it was moving. So that might definitely be something.

If it is functioning correctly then what are my steps for testing the ABS module? Or is it just replace it and hope :p
 
#4 ·
Vacuum is the problem ,or lack of it .Problem with the servo and the brake thats closer to the servo will operate first ,with a hard pedal .Take off the vaccum pipe from the servo , and plug the end of it first or it might not start up .So you can than start the engine to check it for vacuum. ..
 
#6 ·
Anyway you can check it to find if its the problem Just pull the main vacuum hose and stick you thumb over it . The other way is to sit in the car .Engine off push down on the brake pedal till foot goes to the floor .Then start the car if pedal comes up to normal hight then nothing wrong with the servo .. [vacuum booster]
 
#8 · (Edited)
Unfortunately I can't actually get the pedal to the floor even with the car off, when you push the pedal down it goes down normally until its at about 50% and then becomes suddenly extremely hard like you've pumped up the brakes prior. It does return normally to the regular position when you let off the pedal however.

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I finally rolled it into the garage and the vacuum line coming off the servo isn't leaking as far as I can tell, I even took it off and blew smoke into it with the other end covered and saw no leaks, also tried plugging it and spraying carb cleaner at it.

EDIT:

If the corresponding rear brake is working, it could be a problem in the ABS unit.
Now that its in the garage I took the rear drivers and passenger wheel and both calipers are compressing normally. Going to start diagnosing the ABS system.

What I've done so far:

- Took the ABS sensor out of the affected wheel and it was covered in a good layer of crud, cleaned it off nicely and blew out the hole it goes into with compressed air. I'm not getting an ABS light on the dash but thought that wouldn't hurt.

- Whacked the ABS pump carefully with a rubber mallet, I read in another thread about this issue that it could help free up any stuck valves in the unit, however that doesn't appear to have worked.

Second Edit:

I've either made things worse or maybe made a bit of progress. Upon removing the hard line from the ABS pump no fluid came out of it, however the pedal now goes down to the floor like there is air in the system.

I'm thinking that since removing the line allowed air into the pump then the valve cant be stuck?

I know I'm going to need to bleed the whole system at this point however I'm not going to do that yet as I'm afraid of doing the entire bleed and still having no fluid at the front driver's caliper. Are there any diagnostics that can be performed on the pump via a computer?
 
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