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Stumped - Weird brake problem
Posted: January 7th, 2006, 6:15 am
by sep42
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
Posted: January 7th, 2006, 1:02 pm
by mazdubber
Are you losing fluid? Does the pedal go to the floor?
Posted: January 7th, 2006, 2:12 pm
by Shades
Maybe your so-called NEW master cylinder is faulty...
Posted: January 7th, 2006, 7:25 pm
by sep42
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.
Posted: January 7th, 2006, 9:34 pm
by jaydog5678
Did you bleed the MC while it was on the car?
Posted: January 7th, 2006, 9:54 pm
by mitmaks
ya ive heard you have to bench bleed MC
Posted: January 19th, 2006, 11:31 am
by mycarhatesme
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.
Posted: January 19th, 2006, 8:59 pm
by lstpier
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?
Posted: January 20th, 2006, 2:40 pm
by mycarhatesme
where is the brake booster located on the RS model
Posted: January 20th, 2006, 2:58 pm
by PATDIESEL
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.
Posted: January 20th, 2006, 2:59 pm
by sep42
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...
Posted: January 20th, 2006, 8:15 pm
by Josh
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.
Posted: January 21st, 2006, 2:40 pm
by David Witherow
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.
Posted: January 22nd, 2006, 7:24 pm
by Gro Harlem
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.