I currently am suffering from an extream case of brake bias problem.

Whenever i step on the brakes, harder than normal to go into a corner... Both of my rear brakes lock up. Stopping from 25mph with a medium heavy foot on the pedal they lock up.

Also, when the rear brakes act normal the fronts will lock up.

Any info on these issues would be appreciated.

-Markus Reschny

Edit : stock brakes, cheap-o' rayosbesto's (sp?) pads... <---Don't flame!!!

 

bump. I am still having the problem... Also note, i was involved in an accident this afternoon due to this problem. The car is fine other than grass stuck in the rims. I was going around a blind corner, about 15 mph faster than i should have been, the sun was behind me, a white ford taurus pulled out in front in me and i had to stop QUICK! the rear end lost it in the apex of the corner and i did a 360 round about into the ditch (shallow).

EDIT: the rears will lock up even with light - moderate pedal application.

So again, any help on this matter would be great!

THank you,
-Markus Reschny

 

hm. a few things I think and I'm by no means a braking expert.

I seriously doubt your proportioning valve is bad. Its a more or less solid piece of metal with simple restrictor plates in it and whatnot.

Try bleeding your brake system. Make sure fluid is getting to each caliper in about the same proportion as any other caliper. If not, this is a good indicator of something wrong with either the piping to or the internals of that caliper.

Next, check your calipers themselves. Rebuild front calipers are relatively cheap from almost any auto parts store (and are original mazda from what I've heard) and thus excellent preventative maintenance. I doubt, if your rears are locking up easily, that you have a problem there, but check your parking brake preload etc... just to make sure.

You didn't mention any dragging effect or apparent brake release problems so if your car drives normally with the brakes not applied, then you probably aren't preloading your rear brakes causing them to lock early -- you'd notice the common dragging brake effect first.

I just rebuild all of my calipers myself and it was not hard but a bit tedious. Took about a half day for all four calipers. Buy LOTS of brake cleaner, a bottle of brake fluid for lubricating the pistons, a brass wire brush to clean the dirt and rust off, etc...

Also, front brakes take a lot of beating. I had a very slight problem with rear lockup but I'm hoping the rebuild will have cured that. My front caliper bores were significantly more worn than the rears though, although the pistons looked pretty much fine. I don't know if that has anything to do with it or not. And I have the 4-piston fronts, even.

 

Also see this excellent and related thread which I found easily by searching...

https://www.rx7club.com/showthread.p...%2A+AND+pitted

 

My car does this under extreme braking from high speeds, but my car is lowered. Lowered cars don't nosedive as much, and the brake proportioning valve might be dependent on the rear suspension unloading under braking. Ie. less braking force per more nosedive . . and when the car has suspension mods it doesn't nosedive as much during braking. That is my hypothesis.

 

One variable you did not mention.

If the engine is at high RPMs and you decelerate into a corner, the engine drag will increase the rear braking effect and cause the rears to lock.

That (drag braking) technique can be used in autocross to swing the rear around in a hairpin turn.