SHRKBIT

Hi, all. So I've got this strange situation with the brake pedal feel on my '86.5 5-speed, and I'm hoping this sounds familiar to someone out there. The feel of the brake pedal is very firm, except for the occasional time when it's not.

During that occasional occurrence, the pedal is slack for about an inch (2.5 cm) before it becomes firm. Instead of being firm immediately on application as it usually is, there's little or no resistance to the pedal for that first inch, maybe more, before the brakes start to bite. Lifting off the brake pedal and re-applying immediately brings it right back to its normal, immediately firm feel. This is not an on-the-track scenario, this is merely maneuvering in the parking garage.

I've just determined how to reproduce the symptoms, and can do so without fail: just make a slow, tight turn. It doesn't matter whether it's to the left or to the right, the slow, tight turn ensures that the next brake application will have this initially slack condition. The symptoms do not occur when driving in a straight line. I cannot associate the appearance of the symptoms with any particular event.

More details: a couple days ago I had new brake pads, discs, and SS lines installed at each corner and the brake lines thoroughly flushed. The symptoms occurred both before and after, there was no change in the symptoms with the installation of new parts. Normal usage for this car is track and autocross, and the brakes generally work great. There are 129k miles on the car, but records show the calipers were rebuilt somewhere in the 105k-115k mile range (I forget at the moment).

Any ideas? I have none, but hope to be able to reproduce the condition with my mechanic later this week. Thanks,

Curt

Garth S

Yes, I know it sounds silly....but, is a front wheel bearing loose?

SharkSkin

That's what I'm guessing.

D

Antoine928

That sounds familiar to me.
My GT has exactly the same problem.
So far I have check for leaks, flushed the lines twice, checked for play in the wheel bearings. Everything seems fine.
So i guess my next move will be a the brake master cylinder.

SHRKBIT

When you figure it out please post about it! We've figured out nothing yet. Will post a follow-up soon.

Curt

Antoine928

I ordered a new brake master cylinder. It should be delivered during next week and i will probably replace it next week end. I hope that it will solve the problem.

Dennis Wilson

Brake fluid in the booster (due to a leaking master cylinder) can also cause the symptoms you describe.

Dennis

JohanvdWalt

Have you solved this yet?
My car does the same thing some mornings when I pull out of the garage.
I reverse and turn sharp to the right into the street and brake to put it in drive. It does not only feel slack but also ruff as there is two steps before it brakes. It never happened anywhere else. I've never worried about it as its only about 1cm the moment you push the pedal more than that its as normal.

I had my master cylinder replaced about a year ago so there should be no problem there.

Johan

SHRKBIT

My mechanic has mentioned the master cylinder, too, but neither of us can figure out what that has to do with the fact that the slack pedal happens with slow, tight turns.

Last week we checked the wheel bearings and re-torqued the rear axle nuts. No change.

This weekend I determined that it happens with every turn that requires 1.25 turns of the steering wheel, but not so much if it's only 1.0 turns of the wheel. Saturday we'll put it on the lift and inspect it closely from below--because we're still convinced it has to do something with the mechanics of turning--and scratching our heads when we find nothing wrong....

Curt

heinrich

Here's a theory. You have a rare disability which causes you to momentarily black out every time your arms move in a particular sequence of 1.25 turns of a Porsche steering wheel. At that same time, your brain intermittently (only for a nanosecond or two) loses contact with your right foot, which engages and releases and re-engages pressure on the pedal.

Problem solved.

Gretch

Thought pops in mind that the turning action is perhaps resulting in the rotors pushing the pads back into the calipers for some reason. Something loose, either caliper bolts, hats not seated, could cause this symptom.

SharkSkin

Gretch has a point. If you can, try turning it in the tight circle like you described, then straighten it out and put the car on a rack immediately, without touching the brakes. Use the parking brake. Pick up the car, pull the wheels, and look for excessive gap between pads and rotor. I'm guessing that you will find that one of your front rotors is pushing the pads away from the rotor somehow... but check the rears too!

If nothing else, this will give you an excuse to go for a nice drive to settle the suspension.

D

heinrich

Tough crowd!

SharkSkin

Heinrich:

funny, but I'll blame the fact that I wasn't very far into my first cup of coffe of the morning for my lack of response

D

ErnestSw

Heinrich,
You are describing what is known in medical circles as "Der arm getwisten braken schlacken syndrome".
Very rare----only three reported cases.