Funny Brake: Troubleshooting & Repair Guide

Hi,

"Since Friday, I've been experiencing some strange behavior with the brake pedal: when you press the pedal firmly while the car is stationary, it slowly starts to sink, reaching approximately 80% of its travel."
While driving, you don't really notice it because you can achieve full braking power even with less pedal force.
Interestingly, the effect is not really reproducible; sometimes, nothing sinks at all.
Brake fluid is not lost.

Does anyone have any ideas? Could there be a leak somewhere in the master cylinder, or is a seal failing?

The car is a 1998 Audi A3 TDI.

Best regards, Rainer.

Quote:

Does anyone have any ideas about this? Is there a leak somewhere in the master cylinder, or is a seal failing?

Actually, you've already answered the question yourself, considering how much brake fluid you're displacing. What's puzzling me is that defective rubber boots usually only allow a very small amount of brake fluid to pass through, and the problem appears sporadically.

Have you already read the ABS fault memory?
Is the ABS system free of air?


Otherwise, seal the brake line connections of the master cylinder with appropriate blind plugs and perform another pressure test.

@ Rainer

Have you noticed anything about the brakes yet?

I'd be interested to know where the problem lies, because these vehicles are starting to get old.

Hi,

The error is gone again. I suspect a small piece of debris or splinter that occasionally gets stuck in an unfavorable position.
I won't switch [to a new part] until the problem is constant; otherwise, I'll just install a new [component] myself, and three days later, that pesky piece of debris will find its way back in again...
I haven't read the ABS error codes yet, but it's working perfectly.

Best regards, Rainer.

Now it's happening: the brake fluid is leaking out the back of the brake caliper – the aluminum sealing ring has corroded.

An HBZ has also been newly ordered.

Brilliant from Audi: the sealing rings aren't sold individually, but only as a set with a new brake line. They seem to fail frequently.

Best regards, Rainer.

Hi,

Brief feedback after replacing the rear brake hoses (connection between brake line and brake caliper).
The lines connecting to the brake caliper are sealed with aluminum sealing washers, which have simply corroded away. This has caused the brakes to become air-bound, and later, brake fluid has also leaked out from those connections.
It seems Audi is aware of the problem. New brake hoses were in stock, and the new ones have stainless steel (or at least they appear to) sealing washers instead of aluminum.

Best regards, Rainer.

Thanks, Rainer. Is that an aluminum gasket between the hose and the saddle?
Could you post a picture of that old thing? Then I can get a better idea of what it looks like.
Best regards,
derteileklaus

Quote:

Could you please post a picture of the old thing?

Then I can get a better idea of what it looks like.

Forgot your glasses? Take a look at the date.

BM wrote:

Forgot your glasses? Take a look at the date.

'' Wore glasses ''.
the blind one-armed parts klaus