FB Right front lockup
 

Hi Folks,
I have been battling lockup issues on my autocross car. Under hard breaking the right front locks up. I have tried differnt brake pads, turning the rotors, swapped out calipers and have been bleeding the barkes over and over again. Same thing.

The car is an 85 FB, which run a little heavier on the left side, but a friend with an 82 FB has been having the same issues.

Any ideas?

Are you bleeding the whole system? Or just that side? You might have air in the other side front line or caliper which causes that side to work less. It could be the other caliper as well.

I have been fighting this problem with my '85 for quite some time. Never had a problem with my '80.

Some things I have done, which helped:

- Eliminated the proportioning valve (more rear braking)
- Replaced the front control arm bushings (right inner bush felt OK in car, but fell apart when I took the control arm out
- Replaced tension rod bushings with polyurethane. Got rid of the "loosey-goosey" feel under braking, but next time I'll just go straight to rod-ends as poly sucks for this bushing design
- Adjusted for a little more toe-in so the wheels are pointed straighter when braking

Things which did not help:
- Rebuilt the calipers (not the problem)
- Switched tires side to side (not the problem)
- Removed pad hardware, thinking it was causing a binding issue on the left side (not the problem)
- Replaced pads (not the problem)

It's frustrating. I have half a mind to switch calipers side to side (front-mounting them) thinking that maybe it's some weird flaw in the caliper.

Yes, there is about 75-100lb more weight on the left side than the right, but it shouldn't cause lockup *that* early, or braking pulls.

My idler arm is known good. Is yours?

I thought it was just me. I have checked everything I can think of, yet I still always have the right front lock first. Mine is an 83.
I have developed a theory. Perhaps Mazda designed the braking system so that one front would lock before the other. Since all steering control is gone the instant the fronts lock, having the system designed to lock one before the other will still allow for some control.
Of course, it also could just be that the engine is loading the left side tire more when braking, due to the minor amount of engine braking that is acheived when off the throttle. With the already heavier left side, the extra load just delays the lockup of the left wheel that much more.
Maybe neither of these are anywhere near a factor, but it's a thought.

Glad to see I am not alone here. I have a friend who has just given up and is going to the RE speed big brakes.

I too have changed the control arm bushings and tension rod bushings. I have delrin bushings in the idler arm. Swapping pads from side to side have not helped, so I do not think it is the pads.

When I look at the master cylinder the I see that the stock system has three ports. Two for the front brakes (from two different spots), one for the rears. I am thinking that there is a pressure difference between these two spots. One thought would be to merge the two lines into a block and the take the brake lines off the block this would eliminate a different in pressure.

What do you think?

It might work. If it doesn't then the weight on the drivers side just might be an issue. Anybody here drive a RHD FB hard and have the left locking up on them?

The front brakes are indeed serviced by seperate ports in the MC. Merging the lines may help, but I have my doubts.
I think the issue is more related to the already left side weight bias, compounded by the added weight of the driver, and further enhanced by the engine's braking torque, minimal as it is.
I noticed a marked difference in the right wheel locking, by having a passenger with me. The fact that he weighed about 50lbs more than me, seemed to reduce the wheel lockup quite a bit.
Perhaps this issue is not nearly as prevalent in the RHD versions. I dunno.

Right front is almost always the one that locks first in any car. My guess would be it's the closest to the master. Given the extra resistance to flow in the longer line, I suspect you're getting a tiny bit more pressure in the drivers side caliper.

So what do you do with it? If the brake system is in good shape then the drivers side front is locking up a fraction of a second before the other side, so you're not getting any benifit from changing things.

For future reference, 85 GSL 302, right and left are looked at as you sit in the drivers seat of a car, not looking at it from the front. It sounds like you have the opposite problem from the other cars! Maybe the 302 helps this issue :)

My daily driver is doing this now as well. It didn't used to. Jumping on the brakes is now an event that I need to avoid. Last night coming home, interstate traffic came to a screeching halt. Normally this wouldn't be a problem, but I'm having to steer the car to keep it in the lane. I bought this car new. Locking up the right front first is NOT normal. I'm going to look into the LCA bushings.

Ok, the racing year is over and I can really starting pulling this a part and trying to get it fixed.

I have swapped in another set of brake calipers and I am still having the same results.

I have bleed it a ton (went to BF and picked up a vacuum bleeder).

Took a second look at the MC and both front brakes come out at the same area in the MC, so I do not think it is the MC.

The next direction I will take is the proportioning valve. I know it work on front to rear, but maybe it effects one side of the front more than the other.

Oh ya, I will also re-set corner weights this winter to see if that helps as well.

You may also want to rotate the tires. Another possible reason may be faulty brake lines. Check for wear/bubbles etc. Otherwise, I'd try merging both front ports from the master cylinder together. At least then pressure is sure to be the same between the 2 front tires.

Maybe its this:

quoted from the FSM

Caster right hand side 4 deg 10 minutes +- 30 minutes
caster left hand side 3 deg 40 minutes +- 30 minutes
max permissible difference between sides +- 30 minutes

these settings are for a normally driven car and are different for some reason, why I do not know. maybe as we reset for racing we become so obsessed with having X amount that we do not compensate for the required difference of 30 minutes as stated in the FSM?

any thoughts?

kenn

Can I assume that you've already checked the tire pressures? I had this issue earlier this year, but seems to have gone away since I added new rotors...

Corner weights will affect brake lock up big time. That is a good place to start. A difference in shocks will hurt braking as well. Make sure both struts are good, get them dynoed if you can.

Thanks guys for the feedback, great tip Kenn, I will look at that as well and let you all know the results.

Hey Jeb, sorry to hijack your thread but where do you go for your corner-weighting? I may be going to a GC setup over the winter and would need to set corner-weights myself.

Cheers,

Chris