Brake drag

[L DC]

Hi all.

Indeed. Although not brake master cylinder, it did happen to my '87 QSW's clutch master cylinder, which has same set-up as Audi 4KQ and a similar set-up as Typ44 Audi.

The clutch master cylinder in my QSW resides next to the brake booster and gets all the hot air coming from radiator, which was causing brake fluid to expand and, thus, pushing the slave cylinder slightly, causing the clutch to slip.

NOTE: Upon dis-assembly of the clutch master cylinder, the return port was clogged, which in effect hydraulic fluid had no where to go (when expanded by heat from radiator) but the slave cylinder, causing the clutch to slip.

Maybe the return port of your brake master cylinder is also clogged, and fluid has no way to return when expanding other than going to the calipers?

Replaced the master cylinder and replenished with Ate Racing blue and no more clutch slipping!!!

The hydraulic line, however, still has air in it, causing the pedal to sink to the bottom, specially when the master cylinder gets hot from the air coming from the radiator. 

I need to build some kind of heat shield and/or fresh air duct to direct air to the clutch master cylinder.

Regards,

-Louis




--- On Sun, 7/3/11, Huw Powell <audi at humanspeakers.com> wrote:

> From: Huw Powell <audi at humanspeakers.com>
> Subject: Re: Brake drag
> To: "urq" <urq at pacbell.net>
> Cc: quattro at audifans.com
> Date: Sunday, July 3, 2011, 3:29 PM
> '83 in Europe, '84 in US.
> 
> And IIRC, people have reported this before and blamed heat
> from the 
> radiator fan causing expansion of brake fluid?
> 
> Huw
> 
> On 7/3/2011 1:17 PM, urq wrote:
> > ... there was no T44 in '83 ... I believe '85 was the
> first year for the T44
> > ...
> >
> > The behavior you describe sounds more to me like
> moisture in the brake
> > system ... which may well have damaged the brake
> M/C.  I'd recommend that
> > you try replacing the brake fluid to see if it makes a
> difference.
> >
> > I'm not so sure what the problem with rebuilding brake
> M/C or wheel
> > cylinders would be ... assuming you can buy rebuild
> kits.  As long as the
> > pistons and cylinder bores aren't damaged a rebuilt
> M/C should be safe.
> > Most of the parts you will find will likely be rebuilt
> anyway ... and I
> > think I'd trust my rebuild over many of the ones
> available in the stores.
> > If you don't trust your skills you can find a local
> rebuilder who can
> > rebuild your M/C.
> >
> > Steve Buchholz
> >
> > -----Original Message-----
> >
> > Recently acquired a 1983 Type 44 200. It seems that
> once it gets warmed
> > up, the brakes start sticking heavily. You can get
> them to release by
> > jabbing at the brake pedal a bit, but they'll soon
> stick again.
> >
> > I seem to recall this is a symptom of a bad master
> cylinder. I also seem
> > to recall that the received wisdom is that rebuilding
> the MC is a false
> > economy - is that right? (I'm afraid I'm not gunning
> for longevity here
> > - it needs to last a few months and then the
> interesting bits will get
> > lifted for spares for a quattro).
> >
> > Thanks for help,
> >
> > Richard
> >
> > _______________________________________________
> > quattro mailing list
> > http://www.audifans.com/mailman/listinfo/quattro
> > http://www.audifans.com/kb/List_information
> >
> _______________________________________________
> quattro mailing list
> http://www.audifans.com/mailman/listinfo/quattro
> http://www.audifans.com/kb/List_information
>