[s-cars] Brakes seize up when engine is warm

[Scott Justusson]

The big question is this a 95 3 channel or a 95.5 4 channel system...  If it's 3 channel, it is usually either master cylinder or rubber line failure.  If it's 4 channel, it 'can be' the master, 'can be' the rubber lines, and it 'can be' crud/bad fluid in the master that needs flushing.  If it's been confirmed it's a master problem, the 3 channel is cheap/easy to replace.  If it's 4 channel 95.5 the master is major bucks, and some serious flushing/backflushing of the master may bring it back to life.  BTDT

I tore the two open years ago to figure out the difference between them...  The later 4channel Master has internal discs with very small holes in them that modulate (slow) back flow to the resevoir.  If crud or bad fluid clogs these disc ports, you will experience the symptoms you describe.  I've found in many cases, techs will write off the failure as 'Master Cylinder', which I guess technically it is.  However, I have recovered a few by flushing/backflushing... and then flushing more fresh brake fluid thru them with a bleeder (I'm talking fluid flow by the quartS).  At something like 450USD for the 4 channel 95.5 B-MC, it's worth trying.

BTW, most FLAPS and aftermarket list the 95.5 4channel MC as the same as the 3 channel.  AFAIK, there is no substitute for the 95.5 from the dealer.  They are not interchangeable with the 3channel, nor are the internal parts interchangeable either, bttt.

HTH and hope you have a pre 95.5

Scott J
QSHIPQ 

 

-----Original Message-----
From: Thomas Rodriguez <trodri69 at gmail.com>
To: s-car-list <s-car-list at audifans.com>
Sent: Fri, Apr 13, 2012 12:17 pm
Subject: [s-cars] Brakes seize up when engine is warm


The brakes in my '95 S6 started malfunctioning yesterday and I need
some advice on the potential cause.

The brakes perform normally when the car is first driven from a cold
start.  As the entine warms up the brake pedal engages earlier and
earlier until finally there is no play left at all.  At this stage the
brake pedal becomes very hard and grabby as though it's getting way
too much boost. If I continue to drive I can feel the brakes engaging
on their own with progressively more pressure the longer I drive.
Eventually the braking pressure becomes so strong that the car cannot
be driven without smoking the brakes.  If the car is allowed to sit
for a while and cool down the brake function returns to normal.

When this happened yesterday the brake system warning lights lit up on
the dash board.  The owner's manual instructed me to check the level
of the brake fluid and hydraulic fluid.  I did this and found the
brake fluid level to be fine but the hydraulic fluid level was way
below its "low" mark.  I topped up the hydraulic fluid which took care
of the warning lights on the dash board but the brakes still seized up
the next time the car was driven long enough to warm up.

The car is currently parked until I figure this out.  I would
appreciate advice from anyone who has dealt with this sort of thing.

Thanks, Tom
'95 S6
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