Brakes - normal behavior?

adrial · adrial's Garage

I believe my master cylinder needs to be replaced, but I want to make sure before I do it.

First time I bled fluid, I was bleeding the clutch and didn't realize how much fluid was flowing through - the pressure bleeder ran dry, air pushed through system, fluid still in resevoir. Rebled it, and clutch came back up.
Brakes didn't feel quite right.

Bought SS brake lines, installed, bled 1.5L through, no air bubbles at all for 15seconds+ at each bleeder. On first pump of the brakes, the brakes are kinda mushy (car running, but standing still), on 3rd pump or so the brakes get very very firm. If I push down real hard on the brakes (car still running, stopped), I can get the pedal to the floor. It doesn't take long at all, maybe 5 seconds at the most...more likely 2 seconds. This is what indicates a Master Cylinder problem to me. I've been told that ABS brakes do feel different than non-ABS brakes...

Is my diagnosis/the diagnosis I received correct or is it just air in the system?

thanks,
Adrial

Roger Hall · 02-10-2002, 09:27 AM

check the brake booster

Magnus_944 · 02-10-2002, 09:39 AM

If the pedal drops to the floor and you don't have air in the system or leaks I would say that the master is bad. A friends saab was like this and we fixed it with a new master. But I'm not an expert, so get a second opinion on it.

//Magnus

adrial · adrial's Garage

Roger, How do I check the brake booster?

I know in my camry the test was to turn the car off and pump the pedal...and see what it does, something to that effect. Is it similar on the 951?

thanks,
Adrial

Bob's944 · Bob's944's Garage

Brake booster check... with car off... pump brakes until pedal won't go down, hold the pedal there and start the car. If the pedal goes to the ground, the booster is OK. If it does not, then it is bad. When replacing.. be careful, they made a couple different versions.

When the booster is bad, brakes become extremely hard to depress, like you have to stand on it to get it to stop, but it should still stop.

Roger Hall · 02-10-2002, 06:25 PM

with the engine stoped depress the pedel several time travel distance should not change

depress brake pedel and start engine pedel should move down a little

deprese the pedel and shut off the engine hold the pedel for 30 sec there should be no movement

start the engine run for about 1 min then depres the brake pedel several times travel should decrease with each aplication

adrial · adrial's Garage

Tested...the brake booster is fine.
Air in the system or MC?

Bob's944 · Bob's944's Garage

If it's just air in the system, then the sluggishness of the pedal should stay consistant. If the master cyl is bad, then you'll have varying degrees of sluggishness with bottoming out sometimes and not others. There should be some loss of fluid. DON'T let the reservoir get too low. If you keep it filled always, you'll not have to deal with bleeding the clutch.

AFJuvat · 02-12-2002, 06:02 PM

Keeping with the theory of "Try the simple stuff first", I would re-bleed your brakes again. If you have the ability, I would suggest a pressure bleeder (best) or vacuum bleeding.

Also note, that stainless steel lines will most likely change the "feel" of the brake pedal (Though I was always led to believe that they make the pedal feel firmer)

If the above fail, I would agree with it being a faulty master cylinder.

AFJuvat