Brake Performance Problem

[PeterD]

Hi guys...wondering if you can help with my problem.

My braking system has been pretty much overhauled completely over the years of owning my car, and my braking performance at the moment is shocking. It's been this way for the last 1.5 yrs but the car has been on and off the road so don't know when exactly it started.

The car is an 89 MX6 turbo, 4 wheel disc, with ABS.

I have done

* Rebuilt master cylinder
* Rebuilt all 4 calipers.
* Complete flush of system several times using Castrol SRF fluid
* New DBA rotors front.
* Machined rear rotors
* Newish Bendix Ultimates all round.

Now previously using the Ultimates I've been extremely happy with stopping performance. At the moment it's crap. I have a feeling the problem is related to the ABS pump.

Inital bite is good, and at partial braking the car brakes fine, and quite strongly.

But jam the brakes...say emergency stop, or just hard street driving and the car just does NOT pull up...taking it's time to slow down, and after the initial "strongish" bite, they don't grab any harder regardless of how hard/quick you apply the brake pedal.

If I was to drive down the street at 60/70..and jam the brakes on like an emergency stop. The car starts to brake and then the ABS seems to kick in and not do much stopping or modulating of the pedal. It's almost like it takes over, but doesn't give any braking effort to the system????

Help! I like my brakes...and want them back!

Cheers
Pete

[HoonBoy]

remove your ABS fuse, then test the brakes, if they are good then you will know it is the ABS causing the problem.

[dbasteve]

Sounds like your ABS unit needs checking.
Processor and valves.

It's possibly a valve stuck open.

[PeterD]

Ok...

Have pulled the ABS fuse, which disabled the computer.

Now the car just locks up really easily. So same problem, just minus the ABS.

I guess my question now is...what causes a car to lock it's brakes too easily/quickly.

I did a few hard stops, seems to be the front left that locks more often, but that may be due to road camber. They definately both locked on several occasions.

Pete

[260DET]

Others around here would know more about your particular car but how are the rear brakes performing? Could be that for some reason most/all of your braking effort is going to the fronts.

[PeterD]

Rear brakes are fine.

Rebuilt calipers and new pads.

I'm thinking it's either the Power Brake Unit (Booster) or the brake proportioning valve?

Help!

Pete

[dbasteve]

Had a car with a similar problem a few days ago. (Not Mazda)
The Booster was rooted. Check the vacuum hose as well.

[PeterD]

Help guys!!!

The booster has been checked and is fine.

Vacumm hose appears fine too, and apparently the valve wouldn't cause this problem.

I've taken it to three brake places, and they all scratch their heads...and want to keep the car...which I'm not keen on.

There is a dual proportioning valve on this car, what does it do, and could this cause this problem?

What else could cause this?

Pete

[260DET]

Originally posted by PeterD
Help guys!!!

The booster has been checked and is fine.

Vacumm hose appears fine too, and apparently the valve wouldn't cause this problem.

......................

Pete

What valve is that? The brakes on my turbo were poor, the problem was traced to the one way valve in the vacuum line to the booster. It seemed to be OK but I replaced it anyway and, bingo! problem solved.

Hint, don't assume anything, check every component thoroughly and you will find the problem. End of sermon.:)

[rodhog]

Check the Valve Pete

But on ABS models the Abs unit has the proportioning valve in it.

If it is your problem you should not be able ot lock up your rears when they get light- no weight on them.

[raverboy]

Hi,
I have same car with similar problem. I have relpaced all the brake lines with steel braided ones. My mechanic thinks my master cyl is stuffed, so that the next fix on the list. Hopefully this will aleviate my problem.