dukesauto

90 coupe that is race only. One out of five or so times when the brakes are applied very hard, brake pedal gets rock hard. The abs only works at low grid type speeds in the rain. I have been through 3 brake masters, 2 boosters and multiple brake flush and bleeds. It is not a vacuum prob. I really like power brakes and abs, but I can't drive a car that is not consistent! I've been toying with the idea of after market pedals/masters for a while now. Anyone have a similar prob. and cure?

gbrtng

My bet it IS a vacuum problem. You're describing what the pedal feels like when the brake booster runs out of vacuum. Try instrumenting the vacuum supply line to the booster and recreate the situations. If this is the problem, you might add a supplementary vacuum pump in place of the engine vacuum.

dukesauto

thanks for the reply....but it is not a vacuum prob. i put a gauge on the booster and the supply hose. any other thoughts?

jaa1992

I am hoping the rebuild of my braking system will correct a small problem I've been having with right front early lockup.
What pads are you using?
You may need to rebuild the calipers, they may be sticking.

I'll let ya'll know late feb where I'm at, but I figured with an 18 year old car with original booster, master and rear calipers it was time to change them out. I change my front calipers out at least once a year. My fluid was getting grey without heating the fluid so I think I had original seals begining to fail.

engle1147

Still running the "stock" plastic booster?
Shot in the dark here: Insulate the booster from direct/indirect heat sources.

dukesauto

Thanks for the input. But it is not a caliper prob. I rebuilt my oe calipers, still had the prob. bought new grandsport calipers, same prob. bought wilwood calipers, same prob. the booster is the same story. I know that it is not a vacuum prob.
On a side note the front wheel lock up that you are having I will almost guarantee is a lateral accelerometer. (been there with that prob and fix it with that part) If a brake caliper is causing the tire to lock up then it would pull very hard to that side and most likely smoke while driving. The part is located behind the dash in front of the shifter, it's about half the size of a pack of cigarettes.

gbrtng

Duke: Next thought - disconnect power to the ABS unit - on my 91 it's a red wire in the compartment behind the driver's seat - and try to recreate the issue.
If the problem goes away, the issue is with the ABS system.

With my 91, when the ABS kicks in, the pedal pulses but does not go hard, so I'm clueless as to what's going on with your 90.

dukesauto

if I disable the abs I have no issues with the hard pedal, the front brakes will just lock up on hard type stops

desertmike1

sounds like you Answered your own question.

dukesauto

Look, I really thank everyone for their input. But... I'm not looking for a guess. Has anyone come across this prob before and have a solution? And no, I have not answered my own question. Removing the fuse only rules out mechanical type issues, not electrical or electrical operated parts.(that is why I said I know that it is not vacuum related) Maybe the abs motor/pump/controller. Anyone who works on vehicles knows that this stuff is not cheap and or really hard to come by. I don't mean to come across as a d%ck, but I know a little bit about vehicle repair and diagnostic. I don't have ALL the diagnostic aids at my disposal so I thought I would ask around here to see if someone has had a similar prob. I figured with all the knowledge on this forum that I would get some help, and not get treated like a guy who doesn't know how to chance a tire. Again....I don't mean to sound like an a$$ so if I offend anyone I apologize.