Re: Dragging brakes

[zm@mhcnet.att.com (Zafer Mehmood [209])]

> 	It sounds to me like a master cylinder problem.  The only
> thing that could make all four brakes drag is the master cylinder.
> I've seen it happen on a non-audi type car last year.  
> 
> Has the master cylinder ever been replaced?
> 
> happy motoring,
> Carl DeSousa
> 

No, the master cylinder has never been replaced. But it doesn't leak and
the brakes don't drag all the time. I think that when the temperature
rises, the brake fluid is expanding and is not flowing back into the
reservoir as it should. One experiment I am planning to do is to
take apart one of the brakes, and push the caliper piston in (as one
would do to install new pads) and see if the piston goes in easily and
the fluid level rises in the reservoir. If it doesn't, then something in
the ABS unit or in the master cylinder is preventing the backflow which
could be causing the brake dragging problem. Is this a reasonable assumption?

The other thing I might do is replace the brake fluid again. The day I
changed the fluid was very humid; it was raining and the relative humidity
was probably close to 100%. I noticed that the paper towel I was using to
wipe the fluid off, was feeling wet (as in wet with water) after some time.
It seemed like the fluid was absorbing quite a bit of the moisture. Since it
took me a while to bleed all 4 brakes plus the clutch, the fluid may have
picked up a lot of moisture which could be causing the problem. Brake fluid
is known to be hygroscopic and I guess I picked a bad day to change it.

Zafer


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Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ