front caliper locks up and rear drums gets hot

[vuedoo_sss7]

Need help/advice or if anyone gone through this issue before. 510 with 280zx front brake upgrade, stock rear drums, 7/8 MC.  I put new calipers on, brake line, brake pad, the rear are stock drum was just services by shop everything new but the issue still not fix. My calipers are still stuck, the caliper wont release back this only happen when the car is drive for a few miles when the rotor are hot. Do I need the 280zx mc 15/16 will this help? Or do I need to adjust my brake rod?

[datzenmike]

Check the pedal free play. Push down on the pedal with your thumb. It should move easily for several mm or 1/16-1/8" before there is much resistance. The clevis pin can be removed and the push rod between pedal and master screwed in to add play. Without play the master piston does not fully return to it's rest position and fluid can't return to the reservoir. 

 

Don't forget to tighten the lock nut and for god's sake don't forget the clip that holds the pin in place.

[thisismatt]

Master cylinder push rod needs some free play.

[vuedoo_sss7]

thanks for the help guys will mess around with the rod next.

[datzenmike]

Right now it's only a check for free play on the pedal.

[vuedoo_sss7]

I was able to extend the rod back about half an inch, check the pedal with my thumb like the suggest post and caliper still getting stuck after driving it for a while looks like when then the caliper heats up.  Should I bleed the system again? or get a new master cylinder, if a new one should i go with the 280zx?

[wayno]

My first question would be what master brake cylinder do you have?

You said 7/8ths, but is it a dual or single circuit, was it made for front disc/rear drums?

[vuedoo_sss7]

7/8 off of the 280z.

[wayno]

Do you have the circuits piped correctly, front circuit for the fronts, rear circuit for the rear as it is easy to mix them up.

What your describing is what happens when a drum brake circuit is used for disc brakes, it gets hot and seizes and you have to open the bleeder to release the front brakes, a rod adjusted wrong can do the same thing if it is too tight.

[vuedoo_sss7]

Circuit I assumed are correct from last owner, ill double check with diagram. I'll also try to extend rod back some more and see what happens.

[datzenmike]

The front of the master is for the rears. The rear of the master is for the fronts. Usually the master is marked R and F on the side. If reversed you will have a brake drum residual valve where it should be a disc brake residual valve. Drums require 2 to 4 times as much residual pressure as a disc brake, and the pads will drag excessively.

 

 

Caliper or both calipers? If only one, probably the caliper or the flex line to it. If both, pressure is trapped in the forward system.

[vuedoo_sss7]

Both caliper lock up. brand new flex line on both fronts also.