Sticky brakes...not fixed

[e31jann]

Still have sticky brakes after replacing the internal o-rings in my brake booster. After reassembling everything, my Pentosin leak is fixed, but the sticky brakes persist.

When I first start the car, the brakes do not stick. Its only after 20-30 minutes of driving that they stick. The problem seems to come on fairly suddenly, and the brake pedal feels different when they're sticking (less travel before encountering resistance).

It seems the problem could be any of these:

- corroded calipers (Seems unlikely that all 4 are corroded and they only stick when hot. Possible cause I suppose.)
- bad master cylinder
- ABS pump (this was suggested to me - I don't understand how it could cause the brakes to stick)
- booster (has anybody clearly identified a bad booster as causing sticky brakes?)

Any advice on what to check next?

[ChrisFuture8]

Did you have the sticky problem prior to the changing of the O-ring?

What size O-ring did you replace with?

Did you reassemble the brake booster with all its internal components the way they were assembled originally? Maybe a part or two were inadvertently assembled backward? Any of the internal components bent...cone cup looks okay?

Just throwing thoughts at ya. Hope you get it sorted out soon. Not a quick job when it comes to the brake booster assembly.

Cheers,

Chris

[m10n]

have you replaced the caliper?

[wmealer]

My money's on a collapsed brake line. Had this happen on my e36. Bad brake line was acting as a "check valve" in a sense. Pressure applied would cause caliper to bite just fine, but the bad line would prevent pressure from leaving once pedal was released.

[Bryson]

Mine was the master, same symptoms. Replaced with a slightly smaller e32 master due to cost and better rear balance. After going to the e32 master, brake pedal travel will increase by 6-8% if you decide to try that.

Edit: also possible is that the adjustable shaft from pedal to booster is adjusted too far out and your pedal is 'topping out,' not allowing the brake pedal to be released completely

[e31jann]

Thanks for the advice all. A few responses/thoughts:

- the issue was exactly the same before I rebuild the booster
- I have not tried replacing a caliper
- since all 4 brakes are sticking, a collapsed line seems unlikely, as both the front and rear lines would have to be collapsed.

Master cylinder -- I wonder if there's anything else I can check before gambling $500 hoping it fixes the problem?

[Quackers]

It may be a bit late now but I had a similar problem on a Ford Capri Injection (many moons ago! :-) )
When the brakes were warm they would not fully release. As soon as I released a brake bleed nipple fluid would spurt out and the pressure was released.
It turned out to be the master cylinder not fully releasing pressure.

[shyne916]

It may be a bit late now but I had a similar problem on a Ford Capri Injection (many moons ago! :-) )
When the brakes were warm they would not fully release. As soon as I released a brake bleed nipple fluid would spurt out and the pressure was released.
It turned out to be the master cylinder not fully releasing pressure.

I have the same problem but mine is sticking only on the front driverside after driving 15+ minutes. new brake lines, caliper, and pad. bled it so many times and no bubbles. still won't fix it

[Bluesman]

I would run that test.Get it hot then open a bleed nipple and see if it has pressure built up.

[shyne916]

I would run that test.Get it hot then open a bleed nipple and see if it has pressure built up.

If I bleed it than the brake will release and got stuck after driving for awhile again

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[e31jann]

Finally got around to fixing this -- it was the master cylinder. The brakes only started sticking when the car got hot, so I drove it until they started getting sticky, then stuck an ice pack on the master cylinder. I could immediately hear a creaking in all four brakes as the pressure released. Conclusive enough for me, so I replaced it. Thanks to my dad for the tip on diagnosing this one -- it was driving me crazy!

[TedBobo]

Good to hear.....looking forward to seeing you April 1st.

[master6]

Finally got around to fixing this -- it was the master cylinder. The brakes only started sticking when the car got hot, so I drove it until they started getting sticky, then stuck an ice pack on the master cylinder. I could immediately hear a creaking in all four brakes as the pressure released. Conclusive enough for me, so I replaced it. Thanks to my dad for the tip on diagnosing this one -- it was driving me crazy!

jann,

I found a recall notice on my M6, were the brakes would not release.
It is not much of a notice, and I replaced mine with a 750i M/C
Problem solved!
http://www.allworldauto.com/inv/NHTS...ion_73163.html

[smokum]

does the pedal return fully when sticking?