Rear caliper question???

[2012Boss302]

Anyone ever have both rear calipers lock up ONLY on track?? My rear brakes were dragging enough last track day to boil the fluid. I took it into the shop today and nothing seemed amiss. The pistons screwed in without effort. The slides were clean and moving, I did lube them anyway. So far no issues with street driving today on street pads. I am using Gloc R12 pads in the rear but I'm pretty sure that's not an issue.

 

[EF1]

Are you running with traction control on?

 

[2012Boss302]

I was going to edit. No, I turn Advance Track completely off, not Sport mode, just off. I did check the e brake cables. Both arms were fully seated. These are the original calipers to the car. They only have 50,000 miles on them and who knows how many track days. There has been so much Motul 600 flushed through this thing. The master cylinder is a new OE Ford unit.

 

[EF1]

When you say off do you mean you push and hold for several seconds to disable it or just push the button once and let go?

 

[2012Boss302]

Push and hold the button

 

[EF1]

Okay, so it doesn't sound like advance track is manipulating the breaks causing heat problems. Do you have stock rear rotors and are you still running the dust shields?

 

[EF1]

Also, what fluid are you running and when was it last changed?

 

[2012Boss302]

I have the 14 inch Shelby sized rotors. Ford brackets and no dust shield. Over time, gallons of Motul 600. I flush the brakes before every track day and bleed them after. Last time a complete flush was done was November 2023.

S550 front brakes. Yesterday as I was driving to the shop to swap pads I used the brakes as little as possible. I got off the freeway and pulled into the first gas station. My front rotors were 78°f and the rear were 135°f. I'm pretty sure the rear are hanging up.

After swapping pads I came home the same route, using as little brake as I could. Got home, front brakes were 95°f and rear were 90°f. All I did was screw in the piston.....

 

[EF1]

It sounds like you have covered all the bases on rear brake heat management. If they are boiling it has to be either dragging calipers or you got ahold of some old brake fluid. It is unlikely they are dragging equally. Temps ons the street would lead me to the same conclusion as you dragging calipers. If the slide pins are clean and lubricated it must be something internal. I do not know what else to do but rebuild or change calipers. Was there a temp differential between the right and left side or is their uneven pad wear? It is unlikely that both would be dragging equally. Hopefully someone with more insight will chime in.

 

[2012Boss302]

Equal temperature side to side. Rear pad wear was even albeit cooked....

 

[TMSBOSS]

Our cars have been know to have the traction control turn back on. If that happens, the rears cook.
Do you have the Boss 302R/S ABS module?

 

[stevbd]

There are lots of reports of the S550 front 6 piston calipers leading to a soft brake pedal when used with the S197 master cylinder. I wonder if your setup is leading to a front rear brake balance issue, where on braking you are effectively pressurizing the rear calipers more than the front. Have you tried refitting the stock 4 piston front calipers? What front brake pads are you using?

 

[2012Boss302]

Our cars have been know to have the traction control turn back on. If that happens, the rears cook.
Do you have the Boss 302R/S ABS module?

Stock ABS module

 

[stevbd]

Traction control on or not the rear brakes should not be consistently locking up before the fronts, that is dangerous.

 

[EF1]

Traction control on or not the rear brakes should not be consistently locking up before the fronts, that is dangerous.

I don’t see where anyone said the rear brakes were consistently locking up before the fronts. Am I missing something?

 

[EF1]

Equal temperature side to side. Rear pad wear was even albeit cooked....

Usually a sticky caliper or traction control issues show on one side or the other. They both cause problems with wear and heat but not usually equally on both sides. How long were the R12s on the car and what fronts were you using?

 

[67GTA]

I have the 14 inch Shelby sized rotors. Ford brackets and no dust shield. Over time, gallons of Motul 600. I flush the brakes before every track day and bleed them after. Last time a complete flush was done was November 2023.

S550 front brakes. Yesterday as I was driving to the shop to swap pads I used the brakes as little as possible. I got off the freeway and pulled into the first gas station. My front rotors were 78°f and the rear were 135°f. I'm pretty sure the rear are hanging up.

After swapping pads I came home the same route, using as little brake as I could. Got home, front brakes were 95°f and rear were 90°f. All I did was screw in the piston.....

What compound front pads are you using and what tires? I’ve had the backs drag like that as well and seemed to help with a “reset” of the pistons. It’s almost like the ratcheting mechanism from the park brake holds too tightly and won’t fully release.

 

[stevbd]

I don’t see where anyone said the rear brakes were consistently locking up before the fronts. Am I missing something?

I may be misinterpreting it but that is how I read the first two sentences of the first post together with post #8, "I'm pretty sure the rear are hanging up." You are correct, the post does not say "consistently" but that is how I read it.

 

[EF1]

I may be misinterpreting it but that is how I read the first two sentences of the first post together with post #8, "I'm pretty sure the rear are hanging up." You are correct, the post does not say "consistently" but that is how I read it.

When I hear hanging up or dragging I think not releasing completely. That is what confused me.

 

[EF1]

What compound front pads are you using and what tires? I’ve had the backs drag like that as well and seemed to help with a “reset” of the pistons. It’s almost like the ratcheting mechanism from the park brake holds too tightly and won’t fully release.

Good point, I didn’t think about the parking break causing the problem. I almost never use it.