MPLSrx7

had the same problem. my caliper was leaking where the e brake went into it. i rebuilt the caliper and its good. try to rebuild your calipers. it only takes about a half hour once you get it off.

rgordon1979

iTrader: (3)

Alex, I would try to find a new proportioning valve. I am not 100% on this, but I thought I noticed your rear wheels lock up briefly going into that first sweeper at one point.

alexdimen

iTrader: (13)

thanks, i think i'll make that my next step. i've gotten brake bleeding down to a science by now so it won't take that long heh. hope to see you next time if it's not too cold.

rotorhead_izzy

iTrader: (36)

i had this same problem in my bronco II. i know its not nearly the same as a fc, but i did all that you did and it turned out to be the proportioning valve. good luck.

alexdimen

iTrader: (13)

It was worth a shot, but I'm pretty sure it's not the proportioning valve because I switched it out for another one and it made no difference. The brakes feel exactly the same after the swap and repeated bleeding at all points.

I examined both the valve I took out of my car and the one I put in by disassembling them and inspecting the components. Both were in excellent condition: they had no corrosion, the seals were pliable and undamaged, and no passages were clogged.

By the way, I got my wheels to lock up on my gravel driveway. The fronts locked up... I don't know what else to do. I think I'll have my boss drive it on tuesday and see what he says.

alexdimen

iTrader: (13)

i got an experienced mechanic to drive it and he said he had no idea what is wrong with it. his exact comment was, "is that mazda's idea of ABS or something?"

he was joking of course and said maybe i should try a new brake booster. i'm skeptical of this solution since the one i put on there already looked relatively new and passed the vacuum test.

rgordon1979

iTrader: (3)

When you changed the brake booster did you push the brake pedal to see if it or the rod was binding on anything? I really want to get your car over to the garage whenever I get back into town and get this figured out....

alexdimen

iTrader: (13)

that's funny... actually, i just tested that tonight. i pulled the MC off to the side and had my dad press the brake with the the car running.

the booster moved perfectly and the rod came out 1 7/8" with the pedal to the floor. i then checked one of my spare master cylinders to see how far the piston moves in it, which i measured to be 1". that means that the brake booster is doing it's job and fully engaging the master cylinder.

to me this means that the pedal stopping half way down is from the master cylinder bottoming out. since there is no air in the system this means something else is giving just enough that i get some braking, but don't get full braking before the master cylinder displaces all that it can.

that leaves the soft lines and calipers if i'm not mistaken... i'm leaning towards calipers since i already felt the soft lines for swelling.

rgordon1979

iTrader: (3)

Yeah, I would pick up a rebuild kit and bring it all to the garage. We could sandblast everything to get it nice and clean before putting it all back together.

alexdimen

iTrader: (13)

UPDATE:

I decided to measure the rotor temps after some high speed braking (80 to 0):

I used an infrared thermometer...

Fronts = both were close to 280 deg F
Rears = both were around 230 deg F

I then decided to try and lock my brakes up again and see what happened:

I could only get my rear brakes to lock up on pavement. The pedal would seem to bottom out half way down to the floor as it usually does. If I pressed harder, the rears would lock up and the back end of the car would start to come around from loss of traction.

rgordon1979

iTrader: (3)

I think your front calipers are shot.

I won't say I told you so about the rear brakes locking up.......

alexdimen

iTrader: (13)

Only time and money will tell who can say "I told you so". hehe

Did you ever get that fan working? I still haven't gotten down to those parts cars yet.

rgordon1979

iTrader: (3)

haha, i will wait to hear what the deal is.

No go on the fan, but again, i have been so damn busy I haven't had much of a chance to work on it. I think the last thing I actually did was to put it in the day after I got it from you. Do you ever go to the Starbucks meet on Friday nights? I think I will be there this Friday.

alexdimen

iTrader: (13)

Replaced front calipers with rebuilt units. Didn't change a thing.

I also took off a brake hose and blew through it to make sure there were no obstructions.

Everyone that drives the car is baffled by the pedal feel... I'm starting to think regular pedals feel strange myself!

rgordon1979

iTrader: (3)

I think your car is posessed..

alexdimen

iTrader: (13)

I'll just get a roller, swap my drivetrain, burn my old brake system on a pyre under the supervision of a priest, and move on with my life...

This just proves that there are some problems even an LS1 can't solve. *cough*

cezonetheillest

i had a similar issue in an 87 tII. so i took out the abs and bled and bled and bled and it would still go to the floor. so i noticed that fluid was coming out of the master cylinder where the black bushing things are. i replaced those and bled some more and that solved my issue. don't know if that will help you but its worth a shot.

alexdimen

iTrader: (13)

I know there is a lot to read, but I already said that the pedal doesn't go to the floor. It goes halfway down.

rgordon1979

iTrader: (3)

did you use the same single pot calipers or upgrade to 4?

alexdimen

iTrader: (13)

Still using single pistons. Regardless, I've heard that you can use the 4-pistons with the base model master cylinder without problem... may be wrong though.

It's time for stainless lines...

TehMonkay

iTrader: (-1)

Did you check for rust on the hard lines, perhaps that ould be a culprit weakening the hard lines?

alexdimen

iTrader: (13)

There is really no rust anywhere on the car. Besides, if they were leaking, I'd be losing fluid

I have briefly checked the hard lines, but may have missed something. I'm going to check them over in detail later this week.

alexdimen

iTrader: (13)

I finally got stainless brake lines on the car and bled all the wheels down. NOTHING CHANGED! I'm so tired of not getting any results. On the bright side, now I have some pretty brake lines and a nearly bullet-proof brake system after all the components I've replaced.

I'm going back to square one, checking everything over and then I'm going to adjust the brake pedal and booster pushrod and see if I can get anything to change.

note: I pulled my low mile brake booster off of a parts car. After I put it in my car I had to adjust the pushrod to be much shorter to get the proper clearance to the cylinder piston. I thought this was weird but never mentioned it.

alexdimen

iTrader: (13)

I recently had a shop mess with the car and they ended up switching out the proportioning valve spring with some spares that I had. That helped the fronts lock up more than they used to, but my pedal still feels like **** and the rear still brakes more than the front.

Another thing we tried was adjusting the booster pushraod clearance by feel and got it down very low. No real result in pedal feel or braking from that either.

I think I am going to get a rebuilt booster and put it on.

clokker

iTrader: (2)

Are you mixing/matching parts from different years (or maybe even Turbo/nonTurbo)?
I wonder if pushrods vary and that's what the trouble is.
If possible, grab a matched set from a known good car and see if the combo MC and booster is where the trouble lies.