Residual pressure in front brakes

5000Lover · 08-17-2001, 08:05 AM

I have an '89 200T, When the car gets hot, like after driving an hour on a hot day, The front brakes build up residual pressure in the lines. It gets to the point that its like driving with my foot on the brake. Any ideas what this could be? Master cylinder? Air in the lines?

Thanks

ARK · 08-17-2001, 09:03 AM

SteveAngry · 08-19-2001, 07:45 PM

It's a worn out Master Cylinder. As it heats up the piston gets stuck in the bore and you end up with dragging brakes...

I bet if you let your car cool down the brakes work fine, right?

Makes you wonder why Audi would design a radiator fan that sucks hot air out of the radiator and deposits it towards the MC? Surely can't help braking on a hot day IMHO...

Steve Ankney
88 5000
Holland, MI

5000Lover · 08-20-2001, 07:24 AM

I vacuum bled the brakes this weekend. I thought maybe old fluid or air in the lines could be the problem (air could expand when hot). Also vacuum bleeding the brakes may dislodge any debris cloging the vent orfice on the MC. If not, then I'll do the MC next weekend. BTW, an old cruise control vacuum pump, a mason jar, and a few fittings and tubes make an awesome vacuum bleed system.

P.S. Your right, it only does it when overly hot.

Silky5000s · 08-20-2001, 09:50 PM

i have the same problem in my 5k. as far as i can tell, it's actually due to low-heat brake pads, they overheat and swell and force the caliper out. i figured it out when i was driving, and a sprinkler sysytem sprayed on my wheel and the brake violently let go of the disc.

Silky5000s · 08-23-2001, 07:24 AM

it make my car have two speeds; go (slowly) and stop.

Johnny-cat · 09-21-2001, 05:20 AM

Yes it is. I had the very same problem, I replaced the M/S and the problem is gone. You can get one rather cheaply!

08-17-2001, 09:03 AM	#2
ARK AudiWorld Senior Member Garage is empty, add now Join Date: Mar 2000 Posts: 1,947	Sometimes the internals of the rubber brake lines disintegrate, creating a one-way valve...seen it !

08-19-2001, 07:45 PM	#3
SteveAngry AudiWorld Super User Garage is empty, add now Join Date: Apr 2000 Posts: 7,277	My guess... It's a worn out Master Cylinder. As it heats up the piston gets stuck in the bore and you end up with dragging brakes... I bet if you let your car cool down the brakes work fine, right? Makes you wonder why Audi would design a radiator fan that sucks hot air out of the radiator and deposits it towards the MC? Surely can't help braking on a hot day IMHO... Steve Ankney 88 5000 Holland, MI __________________ 1998 A6q 1986 5ktq: Megasquirt EFI and a lot of other mods your car probably doesn't have...

08-20-2001, 07:24 AM	#4
5000Lover New Member Garage is empty, add now Join Date: Feb 2001 Posts: 23	Re: My guess... I vacuum bled the brakes this weekend. I thought maybe old fluid or air in the lines could be the problem (air could expand when hot). Also vacuum bleeding the brakes may dislodge any debris cloging the vent orfice on the MC. If not, then I'll do the MC next weekend. BTW, an old cruise control vacuum pump, a mason jar, and a few fittings and tubes make an awesome vacuum bleed system. P.S. Your right, it only does it when overly hot.

08-20-2001, 09:50 PM	#5
Silky5000s New Member Garage is empty, add now Join Date: Oct 2000 Posts: 64	Re: Residual pressure in front brakes i have the same problem in my 5k. as far as i can tell, it's actually due to low-heat brake pads, they overheat and swell and force the caliper out. i figured it out when i was driving, and a sprinkler sysytem sprayed on my wheel and the brake violently let go of the disc.

08-23-2001, 07:24 AM	#6
Silky5000s New Member Garage is empty, add now Join Date: Oct 2000 Posts: 64	at that point... it make my car have two speeds; go (slowly) and stop.

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09-21-2001, 05:20 AM	#7
Johnny-cat New Member Garage is empty, add now Join Date: Sep 2001 Posts: 106	Re: My guess... Yes it is. I had the very same problem, I replaced the M/S and the problem is gone. You can get one rather cheaply!

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