Stumped - Weird brake problem

sep42 · Post by **sep42** » January 7th, 2006, 6:15 am

So the symptoms are.. the brake pedal has no pressure and no braking power, but only after the car has driven in gear for a about 100m. After pumping a few times, during drive, the pedal regains the pressure and the brakes work. This stays on for a few minutes, and the brakes work good. Then after normal drive - crusing in gear without shifting or braking - the brakes lose any pressure again, pump, works.

Changed the master cylinder and re-bled the system, and it's still the same.

Also, when the car is off, pumping the brakes - they get firm and they stay like that, so no apparent leaks of fluid or pressure that way...

Any ideas at all???

Thanks

mazdubber · Post by **mazdubber** » January 7th, 2006, 1:02 pm

Are you losing fluid? Does the pedal go to the floor?

Shades · Post by **Shades** » January 7th, 2006, 2:12 pm

Maybe your so-called NEW master cylinder is faulty...

sep42 · Post by **sep42** » January 7th, 2006, 7:25 pm

There's no fluid loss, not any that I can see. The brakes work ok when it's parked, when it's revved in neutral, or if I press clutch and brake at the same time (or hold clutch)...
As soon as I put it in gear, and the car moves a little the brake pedal drops to the floor when I press it.
Pumping it restores the pressure for a while..

It could be the MC. I got it from "lstpier", he had it in storage after he upgraded to 929MC.

The problem is exactly the same with my old MC as well.

jaydog5678 · Post by **jaydog5678** » January 7th, 2006, 9:34 pm

Did you bleed the MC while it was on the car?

mitmaks · Post by **mitmaks** » January 7th, 2006, 9:54 pm

ya ive heard you have to bench bleed MC

mycarhatesme · Post by **mycarhatesme** » January 19th, 2006, 11:31 am

my car does the same thing...it affects idle too.

if u double pump the brakes each time your going to stop, it helps.. just a tip.

lstpier · Post by **lstpier** » January 19th, 2006, 8:59 pm

By no pressure on pedal, do you mean pedal goes to the floor? Have you checked that the brake booster hose to the IM and check valve are OK?

mycarhatesme · Post by **mycarhatesme** » January 20th, 2006, 2:40 pm

where is the brake booster located on the RS model

PATDIESEL · Post by **PATDIESEL** » January 20th, 2006, 2:58 pm

It is the black drum looking thing just behind the master cylinder.
It is the thing that holds the vaccum and uses it to help the brakes. I'd bet that the booster is what is causing the problem. You can get them pretty cheap from RockAuto.com
Also it is a good idea to replace the vaccum hose that runs from the intake to the booster. You have to buy that from Mazda since it has a one way check valve and it bent to fit between the intake and booster, but they don't cost much.

sep42 · Post by **sep42** » January 20th, 2006, 2:59 pm

The brake pedal goes down almost to the floor. There is still some braking force left, but not much.

How would I test the check valve? I've done the pumping of the pedal when the car is off, and the pressure holds. It releases when the car starts too.
I think that tests the brake booster tho...

Josh · Post by **Josh** » January 20th, 2006, 8:15 pm

either you have a vac leak on the booster or the one way vlave in the vac line is sticking. i had the same problem. i just took off the vac line and used carb cleaner in it and it started working again.

David Witherow · Post by **David Witherow** » January 21st, 2006, 2:40 pm

is there a chance it cuold have something to do with the clutch line possibly having air in it......cause they feed from the same fluid resevoir do they not.

Gro Harlem · Post by **Gro Harlem** » January 22nd, 2006, 7:24 pm

Sounds like it could be either or a combination of:

1: shitloadz of air in the system...BLEED IT PROPERLY

2: a leak in your vaccuum system or brake booster.

Check the brake booster hose for leaks and re-bleed your system properly.