Miata Front Brake Problem

[Aged racer]

Got a front brake problem I need help with. Car is a '99 former SSB, been converting it to SM this summer. Put all new Mazda OEM rotors on front and back and new Carbotech pads front and back. Adjusted the rear pads OK. Installed the steel lines. Bled all four corners w/ new fluid, etc. Drove it around the block, everything's cool.

Went to roll it around the garage today and it won't move! Both front brakes are locked down on the rotors. It'll move if you drive it, but you can feel the resistance. Never seen a front brake issue like this before. Any suggestions?

TIA- Steve

[Greg Amy]

I suspect a crimped or damaged line, bad master cylinder, or binding of the new pads in the sliders.

Basic troubleshooting: if it worked fine before you did all this work, then re-check everything you've changed...

[chuck baader]

If the car has been sitting, the calipers could be corroded and locked up when you pushed them all the way in. I have had that happen...replace or rebuild. Chuck

[zracre]

take the pads out and see how free the pistons move in the calipers. Open one of the bleeders and see if it moves any easier...that will tell you if it is the caliper or something beyond the caliper. If it is not easier then you know to rebuild/replace calipers. If it is easier, hook up line into caliper and disconnect at the top of the line...this will tell you if it is the line or beyond line. Repeat until you get to the master. Of course as Greg says check all the sliders and make sure they are in right...good luck!

edit: also check that you rotated the pistons in the rear all the way in...

[Aged racer]

Very good tips, many thanks. With both front brakes stuck, I was thinking Master cylinder, but when those fail I've only had mushy pedals and excess air, not the opposite. Plus the rears seem fine, would think a bad master would affect all four corners.

The car has not been run much, the last time back in November. The front pistons retracted just fine at pad install, but I will check their in and out movement first. Would not think the lines, they are new SS.

I have a spare new Master, but hate to replace unless it's the likely culprit.

Thanks again, really appreciate your help !

Steve

[tnord]

are you sure it's the front brakes? jack it up on all fours and try to turn by hand.

the reason i say this is you could've adjusted the rear set screw too tight. i've seen one new guy show up for his first race and pulled in with his rear brakes on FIRE from this. FIRE on MIATA REAR brakes. i adjusted his set screws and all was good.

you'll want to do this anyway to lower the rolling resistance of the car. but progressively tighten the set screw and turn the rear wheels until you can start to feel extra resistance. back off 1/4 turn from here.

[Aged racer]

Yes, I spent some time on the rears, actually I probably have them a bit too loose. Kept thinking they were too tight, finally jacked up the front of the car and that's when it was obvious that both fronts were too tight- can't turn them at all by hand.

Did some more pondering last night. The pistons can't be frozen inside the caliper because they are extended (thus locking the pads down against the rotor). Since they can't/ won't retract, I'm thinking now that system pressure is high, not low. Wondering now if I did something wrong installing the SS lines. Will probably try putting the old lines on first, see what that does.

It's a weird deal.

[ddewhurst]

Have you cracked the front bleeder valves to relieve the possible pressure & the tried turning the rotors ?

[Aged racer]

Update- tried to bleed the front brakes, not much came out, and the rotor didn't turn. Loosened the brake line where it attaches to the caliper and instant relief! Opening the system at that point relieved the pressure on that one wheel. Did the same on the RF. Both now spin freely, but as soon as you use the brake pedal the caliper locks down again.

I'm thinking this means my problem is in the line, since that's the only other variable (did not change the Master Cyl). I must have incorrectly installed the SS lines- will re-install the old ones and see what that does.

Thanks for the help and suggestions-

Steve

[ddewhurst]

***Update- tried to bleed the front brakes, not much came out, and the rotor didn't turn.***

This whole little story ^ don't make real good sense long distance. Are you saying you had someone pumping/holding the brake pedal & "not much came out" ? Are your bleeders pluged ?

***Loosened the brake line where it attaches to the caliper and instant relief!***

This same thing ^ should have happened when you bleed the brakes.

*** Opening the system at that point relieved the pressure on that one wheel. Did the same on the RF. Both now spin freely, but as soon as you use the brake pedal the caliper locks down again.***

When the brake pedal is released maybe the fluid is not reversing it's self through the proportioning valve to the master cylinder resivor (sp?).

A question to ALL. Do the quad/o-rings on the piston help the piston return when the brake pedal is released ? Maybe the quad/o-rings are spent from HOT brakes/fluid.

[ner88]

Does fluid flow from the lines?
Sounds like the new lines may have collapsed, possible reaction to the fluid?
What type of fluid did you use? I once saw something like this after someone used auto. trans fluid in the master.

[Aged racer]

Thanks to all for the feedback. Was out of town all week, today I replaced the two front SS lines with the old factory OEM lines and everything worked just fine. I have no idea why, I must have done something wrong installing them. Went ahead and put the old lines back on the rear as well, JIC.

We are now good to go for this coming weekend's CCPS events @ VIR, which is the priority of the moment.

Later this winter I'll go back and try to figure out what happened.

Steve