BRAKES keep locking up.

[jeffdg]

Every since I inadvertently spun out on the track (I hit nothing, no damage *should've* been done...but so it was)... my front calipers keep locking up (well...not actually 'locked' but dragging heavily). Aside from feeling major drag on the car, the brake pedal becomes rock hard. After about an hour of letting the car sit, things free up. Aside from Hawk HP+ pads, the front brakes are stock.

I have:
Turned the new rotors (they were brand new before this track event)
Replaced both front calipers
repacked the inner and outer front bearings (I replaced the driver side inner bearing and inner seal).

The Hawk HP+ pads were also new before the event, and I haven't replaced them yet. (and would like not to have to...but will I need be)

What's causing this? Damage to MC??? Why not the rear brakes then?? Help!

I should mention that I have an '87 TC rearend, a '93 Cobra MC with the Matt90GT conversion kit (3-2 converter and adjustable proportioning valvue replacing the stock proportioning valve).

 

[HISSIN50]

hhmmmm, that sucks. my two cents worth- are you sure there is absolutely no air in the lines. given the info and changes you ve done, thats weird. ive had back brakes do the same to me, but it was cuz they old and needed rebuild (if i kept my foot on brake,they stayed locked up after i released. it was bad seals in caliper.are your (rubber) brake lines new? could there be obstruction and or swelling issue?
just ideas, sorry i not much help. good luck

 

[yosh]

I think I can help you here. Are your lower brake lines colapsing? How long does it take for them to start dragging? Does the drag get worse as you go? I had this problem and changed everything. I changed the lines, proportioning valve, calipers, rotors, and master cylinder and never solved the problem. It took a year for me to find the problem. No dealer or mechanic could help me. I called everyone. Finally My oldtimer mechanic was the only one that knew what it was. If you have have done all the things that I mentioned above and none of it worked I will help you. It should take only five minutes and a 9/16 wrench.

 

[jeffdg]

onto something...

Yosh, I think you may be onto something...

In the last two months, I have replaced the MC, put the new proportioning valve in, replaced the pads, rotors, inner bearings, outer bearings, inner bearing seals, calipers, and the guide pins. Other than your suggestion, there is an outside change that my brake booster post is out too far (I recall messing with it the day before my spinout, but the brakes were totally fine until I actually spun out, which wasn't right away).

It takes a couple miles for the brakes to lock up, and if I don't use the brakes, I can drive pretty far (hundreds of miles)...but as soon as I hit the brakes - they'd lock up.

 

[yosh]

There you go. Just loosen the bolts up on the booster to master cylinder and take it foer a spin. If they dont lock up on you then you know that was the problem. I just put a couple of washers in there and it fixed my problem. It only takes that shaft sticking out 1/32" to make this happen. But you better fix it b4 you crack your new rotors.

 

[rd]

There you go. Just loosen the bolts up on the booster to master cylinder and take it foer a spin. If they dont lock up on you then you know that was the problem. I just put a couple of washers in there and it fixed my problem. It only takes that shaft sticking out 1/32" to make this happen. But you better fix it b4 you crack your new rotors.

My guess would also be that the pushrod from the power booster to the master cylinder is sticking out too far, and does not allow the master cylinder to return all the way home. Had this on a 76 Scout a couple years ago, changed the mc about 3 times. It would lock the front brakes on real hard, had to bleed it to drive it from a stop sign. Adjusted the pushrod, fixed it.

If it was just one caliper, I would say the caliper is stuck, either the piston, or the slides, but with both, guess one is the pushrod, and guess two is the brake lines, but that should only affect one side.

 

[Matt90GT]

Everything was working fine, then you crashed/spun out.

Hrm, I would think that you may have bent a spindle or crushed a metal brake line there. I would suggest inspecting the spindles

 

[jeffdg]

Everything was working fine, then you crashed/spun out.

Hrm, I would think that you may have bent a spindle or crushed a metal brake line there. I would suggest inspecting the spindles

wouldn't a bent spindle show wheel wobble? Or at least it would only happen to one side? This happens to both sides and they free up at the same time... What would I be looking for in a spindle inspection? I just had the rotors off and they 'looked' okay... but I'm not exactly sure what I'm looking for with regards to the spindles. The wheels spin freely (without wobble or other weirdness) when it's cold.

I'll check the MC post length first and report back.

 

[jeffdg]

I think the MC thing did it... what was precarious was the timing of it all, was a red herring - spinning out was just a timing thing (so my theory is... that hindsight thing again.

Thanks guys.

 

[StangPowerSoon]

If you havent already cured your problem Jeff, another thing you might want to check is your suspension system. A ruined Leaf, spring or a worn strut can cause your pads to brake by applying extra pressure to the axle. =P