951 Brake problems

Porsche Technical related discussions.

951 Brake problems

Postby thofmann on Tue Aug 25, 2009 6:09 pm

I need some help with the brakes on my 1986 944 turbo. They work just fine driving in normal traffic and provide good deceleration with little force on the pedal. However, it takes an extreme amount of force to lock up the wheels.
My first guess was that the brake booster runs out of steam at maximum force. So I disconnected the vacuum line from the booster and took a test drive. It took a lot of force to drive in normal traffic, but now it was impossible to lock up the wheels. Therefore, it seems that the booster does what it is supposed to, but for some reason the brakes have become very non-linear.
I put in new brake pads and brake fluid with no effect. When bleeding the brakes, the brake pedal could be pushed in all the way with little force, so it's not like the pedal hangs up half-way.
The brake hoses are of the braided type of unknown vintage. I really don't think that the problem is with the brake lines, hoses, calipers or proportioning valve. The chances that all of them went bad at the same time are pretty slim. Otherwise, either the front or rear axle should still lock up at the usual brake pedal force.
That leaves just the brake booster and master cylinder.
Any suggestions what's going on here are greatly appreciated.
Thomas
1975 911S coupe, hibernating
1986 944 turbo, back from the dead
1986 928 5-spd, temporarily out of service
thofmann
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