Brakes overheated and locked up

[scusi]

On a leisurely back road drive, yesterday. All of a sudden the car was struggling to go forward. At first, I thought it was an engine problem. But the brakes were trying to lock up and I had no travel in the brake peddle it was rock hard trying to depress it. The brakes had gotten so hot that it bubbled the paint on the rims and melted the caps. We had just encountered a small stretch of gravel road and thought maybe a rock had gotten into the caliper. But, all the wheels especially the front were hot. Any ideas on what would cause this?

[kilrwail]

Maybe your master cylinder seized in the "on" position? I've never heard of this, but the symptoms point to something that all wheels have in common, like the m/c. You could open the bleeder screws (one at a time) to see if the wheel(s) will turn freely, having removed the pressure.

[RRoller123]

Vacuum Booster rod adjusted a little too long and thereby causing the brakes to slightly drag. Eventually they overheat and all lock up?

[scusi]

Brakes were rebuilt with new calipers and master cylinder 2 years ago and were working fine until yesterday. Really, pissed that it ruined my wheels. Now, I have to get them sand blasted and repainted or get new mags. (which, is not a bad thing. but, an expense I didn't need.)

[RRoller123]

Master cylinder failure? The fact that all 4 overheated simultaneously leads to the conclusion that it is the central part of the brake system that has failed. If a brake line was pinched partially shut, from an impact, say... that wouldn't effect all 4 corners simultaneously. Not likely that the push rod adjustment would move out on its own, so something in the master cylinder has probably stuck in the pushed position? Is it an old mc?

[DieselSpider]

If one front gets overheated it will back feed to the master and eventually lock up both. Were all the rubber hoses replaced two years ago when the MC and Calipers were? One hose coming apart inside can lock up a caliper until it gets so hot that it pushes fluid past the blockage and back the the Master Cylinder and the wheel on the other side. Not sufficiently coating the Caliper Guides with Silicone Brake Grease after polishing any rust off of them can also lend to this situation. I like to soak the Guide Shims\Wedges for a few hours in a 50/50 blend of White Vinegar and Water to get them clean before polishing them and silicone greasing them.

[DaveMarcotte]

On a leisurely back road drive, yesterday. All of a sudden the car was struggling to go forward. At first, I thought it was an engine problem. But the brakes were trying to lock up and I had no travel in the brake peddle it was rock hard trying to depress it. The brakes had gotten so hot that it bubbled the paint on the rims and melted the caps. We had just encountered a small stretch of gravel road and thought maybe a rock had gotten into the caliper. But, all the wheels especially the front were hot. Any ideas on what would cause this?

exact same thing just happen to me!! Did you find the couse?

[DaveMarcotte]

I cooled off the rotors with a hose. Posted my last reply then started the car and it's back to normal? What happened?

[RRoller123]

Careful cooling hot brake rotors with a hose. They can warp badly, better to let them cool down slowly.

[DieselSpider]

The cause can be maladjusted vacuum booster, failed rubber brake lines acting as a one way valve preventing release or hung calipers from lack of cleaning or insufficient use of a silicone grease on the sliding parts. If the vacuum booster has not been replaced recently then the you should start with the other causes. The brake fluid is likely acidic now and needs to be flushed after being cooked like that.

Brakes need to be flushed and the caliper guides/slide cleaned and greased every 2 years regardless of make and model. This is even more critical on vehicles that see limited use.

Note that if things got hot enough to damage the rims then likely the tires and rubber parts in the caliper were damaged to some degree also.

[BSmith79]

When you apply the brakes a piston in the MC moves and blocks the return to the reservoir and allows pressure to the brake, when you release the piston should move back under spring pressure and allow the pressure to bleed off into the reservoir. A little pressure (about 2lbs) is maintained in the lines to keep the pucks out on discs, higher pressure on drums--the valve for this is called a residual pressure valve

The RP valves are usually 2 each front and rear ---and you have a prob with both ends
You havent messed with the booster input rod adjustment or pedal

sounds like Master Cylinder

it might be working now but park it and pump the brakes hard a bunch see if you can roll the car by hand in neutral---if not open the line to bleed off the pressure

I have yet to look at the brake system for a fiat as I have had mine two days but it will be the same generally as other cars I think

let us know how it turns out