Has anyone experienced any brake booster problems ? I have an ongoing intermittent problem with OVERLY HARD brakes , sometimes I have to literaly stand on the pedal to get the car to stop ! I suspected that it may be because of the low vacuum my ported motor produces at I dle , but when I think back , the idle vacuum is the same as my last half bridged motor at a max of -7 inH2O and I had no problems then . I went through three check valves with no change , I even purchased a vacuum canister to assist the the booster but to no avail , does the booster fail in these cars ? , anyone else experience anything like this ?

 

I've been on here a long time, and I can't recall someone ever having a problem directly with the brake booster. The only typical problem, Mazda addressed in a TSB which had to do with relocating the check valve in the brake booster line away from the turbos and pre-cat.

 

If it's intermittent, I think it's safe to rule out air in the lines, however it might still be a hydraulic issue in the master cylinder.

Dave

 

The booster can fail on any car.

It sounds like you have a leak in the booster somewhere. Here is how to test:

Disconnect the booster from the vaccum line going to it. Attach a line with no check valve. Pull vacuum on the line with a pump that has a gauge on it and a check valve after the gauge (most mityvac types do). The booster should hold relatively the same vacuum for 30 seconds or more.

some other tests:

- Hold the brake down with the car off. start the car, still holding the pedal. The pedal should go down further.

- Note how far from the floor the pedal comes when the car is running. Let the car run, then turn it off without touching the brake pedal. Wait 30 seconds and press on the pedal. It should go down the same distance, then slowly get stiffer each time that you press it again.

 

^ All great tests that will prove if the diaphram inside the booster is good or not. If the diaphram happens to split or leak you will lose some of your power brake effectiveness and also have a vacuum leak that will make the idle unstable whenever the brakes are applied.

 

My FD did not have the check valve relocation TSB either and I experienced similar symptoms. Rock hard brake on occasion most notably first thing on startup.

Bought a relocation kit from Ray and it solved the issue. Verify the TSB by vacuum hose on the driver's side has a lump - the check valve.

 

I've never had a problem with the FD booster. I've had the usual check valve troubles, though. Diaphrams rarely cause problems, and then they wouldn't be intermittent. There is are some valves in the booster called reaction plate & valves by some that I suppose could be problematic.

I had a weird problem with similar symptoms in another car resulting from a partially obstructed vacuum line that also had a leak in it. Sometimes the brakes were fine but I almost plowed into other cars on several occasions where the booster didn't work. Cleared the vacuum line and fixed the leak, never had the problem again.

 

It seems that the problem is in sufficient vacuum ! with my port I only see -5 to -6 inches at idle and the booster needs about -15 for proper function . I had my booster tested and its ok , I plan to get an electric vacuum pump to fix this problem.

 

Make sure to check the vac lines from the intake manifold. I had the similar issue. The car had the brake recall done BUT not done correctly by Mazda. The actually added the new check valve (off the booster) without removing the old one on the passenger side.

To do the recall correctly you must replace the hose/check valve on the passenger side with the hose only and the hose on the booster side is replaced with a hose/check valve.