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Strange brake problem

M

morbid

Hard-core CEG'er
Joined
Feb 10, 2003
Messages
1,750
Location
Phoenix, AZ
I've had an issue where the pedal is firm (not overly firm) but the brakes wouldn't stop *that* fast unless I pushed harder on the pedal. After pushing harder, I can feel the pedal give a little then it starts to brake more. If I get on the brakes hard... the pedal gives a couple times, but it won't slow fast enough to engage the ABS.

At that point... my rotors and pads were in bad shape, so I replaced the fronts with the 13" Baer kit. The problem was still there, but less (bigger brakes). So I moved to the rear and installed the TCE 11.75" kit. The problem is still there.

I've bled the fluid several times... and both front and rear pads are properly bedded.

Now when I replaced the rotors, the rears appeared to be more worn than the fronts, which I was hoping happened because I had too aggressive pads on the rear. Does the above sound like something might be affecting my bias, or does anyone have any ideas?

The rear caliper is the only component after the hard lines that hasn't been replaced. Could they be the problem? Maybe an ABS component? Also I have never bled the master (don't think it's ever gone dry) and also have never actuated the ABS while bleeding (though previously I have actuated it many times on the street).

I'd greatly appreciate any input... thanks!
 
Thanks for the reply Rara! I checked vacuum from the booster end of the booster hose (in case the hose was faulty). Idle was a stable 17. It would drop to ~10 when turning the throttle, and would go up to ~24 when releasing the throttle. It would then drop back down to a stable 17.

I also tested the check valve on the booster hose, which was fine.

From what I could tell, those #'s looked ok. Any other ideas? I really appreciate the help!
 
Does anyone have any more ideas? I have no CELs.... and I'm not exactly sure where to go from here. I'd hate to start replacing potentially good original parts in a witch hunt approach to this issue.
 
still sounds like a booster issue. I would start checking for a faulty booster. Try pulling a vacuum on it and see if it can hold it, stuff like that.
 
Ziyad said:
Leaking seals in the master cylinder?
Click to expand...

this is a possibility, but not the most likely issue from the description of the problem. unless of course, he has been dumping mineral spirits into his master cylinder, lol.
 
I haven't had a chance to hook the vacuum pump directly to the booster yet. I have another problem that I'm trying to fix... and I'm not sure if it's related.

My 1/4 mile times have been extremely slow... so I datalogged it. I found that whenever I get on the gas, the knock sensor goes nuts and my timing goes to crap. I did some testing and I'm 90% certain the sensor has issues and ordered a new one today (1 of 2 left in the US). After a bunch of reading... am I to believe that when this happens, less vacuum is produced? Could this issue possibly be related? I'm still going to test the booster... but I need to get some tubing first. I know it holds at least some vacuum... as I can hear it when I pry the booster hose off.

Oh... no mineral spirits, just ATE :)
 
your engine really only makes significant vacuum when the throttle is closed. This is why the booster has a check valve, so it can retain a vacuum when the engine isn't pulling enough through the vacuum line. The biggest vacuum spike you will see will come when you are at high rpm at WOT, and then slam the throttle shut. So basically, the two problems are probably unrelated.

To be honest, your situation does sound a bit odd; I wish i could drive it for myself and feel it out.
 
Ocassionally I have seen cars with a kinked vacuum hose feeding the booster. Under certain conditions they would constrict enough to completly lose boost. Although I have not seen it on a Contour, it's worth checking.
 
I don't see how our hose could kink without cracking. I also tested the booster line and check valve... no leaks and the valve worked as it should.

I keep thinking of various ways to explain it... because it is indeed strange. It feels like there is resistance when initially engaging the brakes, and it does begin to slow down. If I need to slow down faster, I push harder on the pedal and it'll give, then start braking faster and the pedal feels more normal.

Also... sometimes if I mildly push the brakes to the initial resistance point... if I let off, then get on it again.. it feels more normal. It still usually doesn't stop as fast as it's supposed to.... and if I were to guess about how often the brakes work without problem, probably about 5-10% of the time.

Thanks for all your help guys! I'll have time tomorrow to hook the vacuum pump directly to the booster. If you can think of anything else I should test while I'm doing that... please let me know. Thanks!
 
well, if the booster checks out, the next step is what ziyad suggested; the master cylinder. Though, there isn't a lot you can do to diagnose it individually, most people just replace it and see if that works.

Another possibility is crap clogging up your brake lines somewhere. If this is the case, it is a serious pain to ensure the lines are completely cleared out.
 
This happened to my 89 sable same exact feeling I am pretty sure we replaced the master cylinder and it fixed it. But I am not totally sure this was years ago now.
 
I tested the booster by pumping out 10" Hg of vacuum. After 5 minutes it was still at 10".

Unless anyone comes up with anything else I'll try bleeding the master (never done this before)... and if that doesn't fix it, I guess I'll try a new master. I'm really hoping something didn't somehow get into the lines... that does sound like a pain.

To make sure I understand the master bleeding procedure... some one applies pressure to the brakes and then loosen one of the lines at the master... then tighten it before the pedal is at the floor. Then repeat for the other line. I'm assuming I'll need to try to wrap the master/line connection with shop towels. Does all that sound correct?

Thanks again for your guys help! If you can think of anything else.. please let me know!
 
His issue was definetly vacuum related. Under WOT (not under load though -- neutral) I still have 10" of vacuum. Even his idle numbers were low.

I didn't just want to be pretty sure I didn't have some form of vacuum issue... I wanted to be absolutely sure. So I spray tested for vacuum/intake leaks today and wasn't able to find anything. Thanks!
 
Tony2005 said:
CRZYDRVR had the same issue. You might want to PM him to see what his turned out to be.
http://www.contour.org/ubbthreads/s...er=1162987&page=&view=&sb=5&o=&fpart=all&vc=1

Edit. CRZYDRVR's PM info.
http://www.contour.org/ceg-vb/member.php?u=28874
Click to expand...

My problem ended up being the check valve at the master cylinder. I replaced it once, so I figured it was good. Wrong. Second one worked right and fixed everything. I used a generic one from the HELP section at the auto parts store, since no one had the correct part in stock. I spliced it into the line just outside of the MC.

Still getting a vacuum reading of 0 with the slightest throttle opening though. Cant figure out why, but it isnt causing any problems yet.
 
Last edited:
I have some updates.... At yesterdays autocross, I had absolutely no brakes at the finish line (pedal would not move) for the first two runs.. I then dropped from the event. The brakes worked throughout the course in it's currently funky state though. This leads me to believe I depleted the boosters vacuum through the course to where there was no vacuum left for the finish. After engine braking for what seemed like 5 seconds (probably only 2) the pedal moved.

I'm going to order a new booster line (with check valve) and a new booster grommet. I'm hoping that'll fix it since everything else is expensive and a paint to replace. Seems like the problem only exists while driving.... where all of my tests were in the garage.
 
Did you ever do the throttle hang fix? if so, you didn't put it in the line to the brake booster did you?

Your description now sounds more like a restriction of the airflow, so that you simply have very slow vacuum replenishment.
 
heh... my TH restrictor is in the IAT hose.

Hopefully the booster -> intake tube will fix it. It's possible that the valve might stick or something. I should be getting the replacement tube in a couple hours (waiting for it to get trucked to the local dealer)... so it'll be on tonight.
 
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