Machbin

Hi guys, 83 944 NA here. Trying to sort through an issue with my brakes. The pedal sticks after pressing it. It doesn't return. I have to lift it with my foot. And it's actually applying the breakers when it does this because the car drags when coasting and has resistance when accelerating from a stop. Then when I left it with my foot, the brakes are not applied and all is good. Also if I brake and then leave it stopped, the brake lights are on. I initially replaced the return spring and no change.

Now I am thinking either the brake booster or master cylinder. I have done some generic tests for brake booster problems but seems inconclusive. It doesn't sink when starting the car while pressed and it doesn't rise after turning off the engine either.

Any ideas?

Tripl7

It would seem to me the pistons in the MC are sticking in the bores and the return spring cannot overcome this. Most common symptom of failing MC is leaking past the seals internally and spongy feeling like air in the lines which causes the pedal to slowly fade down. How long has this been going on?

Machbin

Ok, thanks, I'll check out pelican parts for an MC then.

It's been like this ever since I purchased the car, I've been trying to sort through the 3+ owners many issues and this is one of them...

V2Rocket

booster has a big spring in it that i would assume does a lot of the "return" action.
but i would be more inclined to think the MC is suspect.

how does the pedal feel? ive never seen/noticed the 944 brake pedal sinking with the engine on, but it does in my Subaru.

Machbin

There's about an inch or so of play at the beginning that I can move in and out with my foot. Then after there's some resistance of the actual pressing of the brake, but it is stiff and there's not much room to press the pedal in.

Guess that's two votes for MC...

odonnell

Here's a test you can do. When the pedal sinks to the floor, kill the engine. Does the pedal come back up? If so, it's likely that something is wrong inside the booster. The vacuum is valved as the shaft advances but the 2 chambers in the booster are supposed to be equalized when the pedal isn't being pushed, therefore no power brakes sucking the shaft forward.

I have a 2-part video of what's inside the booster and how it works, if you search "porsche 944 brake booster" on youtube.

Machbin

No, it doesn't come back up... But it doesn't sink when off and the cars turned on either (I read that is another test)

V2Rocket

944 brake pedal with a dead/faulty brake booster is like stepping on a rock...nothing happens, but it's hard, lol.

Machbin

When you say nothing happens you mean the pedal doesn't move or the car won't stop if the booster is bad?

Mine is stiff, but I guess not rock stiff. And then it has a small amount of play and then moves when I pull up with my foot.

Still sound like MC?

V2Rocket

No, the pedal moves when you put foot pressure on it.
But without a functional booster the pedal effort is unbelievably hard to push down, so you get very little braking action.

Machbin

Gotcha. So this seems like it's all pointing at the MC then, thanks for your help everyone.
I checked everywhere online and paragon has then the cheapest.

CliveB

My money is on the pedal box. This is a not uncommon problem with the clutch pedal.
Cheap test is to squirt some lube on the area around the pedal pivots and wiggle the pedal to get the lube in.
Worth a try...
(If you are right hand drive there are other bearing points on the shaft across to the brake booster.)

Machbin

So I finally got some work done. New master cylinder, new hose from resevoore to clutch. Swapped it out and bled entire system. No change (except my clutch feels great now). The pedal still sticks....

I do have this intermittent idle drop that I thought was related to the throttle body, but could it be a vacuum leak on the booster system?

I guess time to move to the booster? Or booster check valve? Any symptoms of one vs the other?

benchod

I would take the booster out and look at the rod that connects to the pedal. It that has a slight bend in it, it could cause a similar symptom.

Machbin

Another observation I have noticed is that the pedal normally returns to within about 1/2" of it's top most position. However if I press in the clutch, the brake pedal pops back to top. And this is with a new mc and bled system. How could these be related?