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SprintStar · Joined: 26 Aug 2003 Posts: 150

My brakes are usually fine. Then one evening, the pedal sank to the ground as I was slowing down at a junction. It is not an isolated incident. The next few stops had me pumping the pedal to get braking pressure.

Strangely after that night, the brakes have been firm to date. What happened back then? I wasn't driving fast or racing or anything, so I don't think that was my brake fluid boiling....

Thanks for any suggestions.

Sprint.

Lizard · Posted: Tue Apr 13, 2004 10:35 am Post subject:

could have been maybe a air pocket which may have found its way out.
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3 928s,

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

Sometimes cold weather can cause a seal in the master cylinder to shrink and allow fluid past it instead of building hydraulic pressure. Everytime I've had an mc go bad it's in cold weather but that's not an exact science, that's for sure. Maybe more coincedence than anything else but that's the explanation I got from a very good mechanic. Or you may have some schmutz (technical term) in the mc that wedged itself between the seal and the wall of the cylinder for a little while and then worked it's way past after you pumped the brakes a few times.

Usually, if you have air in a hydraulic line it won't work it's way out. The lines would need to be bled to get it out. Usually. When's the last time you changed the fluid and bled the brakes?

Smoothie · Posted: Tue Apr 13, 2004 12:46 pm Post subject:

I had the same thing happening occasionally in cold weather, but not quite as bad. Finally got around to rebuilding the brake MC the other day. Messy and a little time consuming, but it got done. The special tools used were a brake cylinder hone and snap-ring pliers. I bench bled the MC after rebuilding it, installed it, then bled the brake lines.

Old parts and new with springs attached -

Clean reservoir and brake fluid are supposed to look like this...who knew? -

Brake cylinder hone -

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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

MunkPuppy · Posted: Sun Apr 25, 2004 12:15 am Post subject:

hey Smoothie, I noticed that your brake fluid reservoir has electrical connections coming from it. Mine does not. Does anyone know if this fluid level indicator was not included in the 80 931?
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'80 931 FOR SALE

"It's a shame that stupidity isn't painful"
-Anton Szandor LaVey

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

FWIW, my '79 931 does not have the low-fluid-level sensor either. Don't know what year that feature appeared.
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'79 Eurospec 931

Smoothie · Posted: Sun Apr 25, 2004 2:33 am Post subject:

According to the parts list, the changeover was between '80 and '81. From '81- on (also pre-'81 with option M592) got the cap with the low-level warning sender.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox