Rear Disc Brakes Hanging Up

[bbab3]

I have a brake system that is far from stock. I am using a hydroboost froma Chevy Astro van, an aluminum style Mopar master, A-body drum-drum distribution block, front disc Mopar 11" and Ford Explorer rear disc setup on a 9" rear axle. After bleeding the power steering pump and hydroboost the brakes worked way better than before, with one exception the rear brakes are hanging up. Additionally, it is possible that the rear discs were having this problem before the install of the hydroboost. Any suggestion on where to start since the master does not have a residual valve? Thanks

 

[67Dart273]

I am not familiar, specifcally, with those calipers/ brakes. Sticking pistons comes to mine. Where were they sourced, and are they new, rebuilt, or used? Is it possible the parking brake is involved. I would first make CERTAIN that the hydraulic pressure is not somehow residual, by cracking a tube/ hose fitting after applying the brakes, and go from there

 

[Dubob]

Only thought I have is the push rod from the hydro boost is too long not exposing the compensating ports on the master cylinder to allow fluid to flow back to reservoir upon brake release. You could crack the bleeders to see if fluid is trapped in caliper and if piston retracts. If so, pump them up and crack the rear line at MC to see if they release. That would help determine if it’s at calipers or up stream.

 

[Inertia]

Does that disc system have internal shoes or caliper emergency ?

 

[4mulas]

Have you confirmed NO residual pressure valve? If your master has a residual pressure valve on the rear circuit to accommodate what should be drum brakes it will make your rear disc set up ‘drag’ or hang up. Check for and Remove the residual pressure valve in the rear segment and remove as required…

 

[bbab3]

Thanks for the advice. I have checked for a residual valve in the master cylinder and the rear calipers still seamed to hang up after disconnecting the brake line. I also have checked that the parking brake shoes are free and properly adjusted. I am going to check the rear calipers and see if the calipers or pistons are binding. Could the piston in the distribution block be the problem?

 

[RustyRatRod]

lol

 

[Inertia]

Thanks for the advice. I have checked for a residual valve in the master cylinder and the rear calipers still seamed to hang up after disconnecting the brake line. I also have checked that the parking brake shoes are free and properly adjusted. I am going to check the rear calipers and see if the calipers or pistons are binding. Could the piston in the distribution block be the problem?

It's not uncommon for caliper pistons to bind or seize, particularly if the calipers are aluminum .
If the emerg shoes are not the problem, I'd be pulling the calipers and putting kits in them.
The rubber seals get hard, and don't pull the piston/s back, - as designed.
(Once the pads are out. Try turning the piston with water pump pliers, grasping the very top of the piston to avoid seal surface damage. If it won't turn, - take em apart.)
They're Easy to do, since emergency brake is separate, - and if you don't know their history.
I didn't see a response to the question of the caliper relaxing after you opened a bleeder or fitting .
So we don't know if there is some form of residual pressure, or just the caliper binding.

Good luck.

 

[bbab3]

To clarify, when I disconnected the rear brake line the binding did not stop.
I plan on taking the rear calipers off making sure everything rebuilt and functional.
The Hydroboost was a concern and I did size the rod that depresses the master cylinder when adapting it to my a body. I did double check by loosening the ms bolts to hb with no change.
It will take me some time to get the calipers apart (to many dr. appointments).
When I do have an idea of what was wrong I will reply. Another fine mess I got my self into.

 

[340sFastback]

When I put new 10.7 rear disc on mine I had two things causing rear brakes to drag. First not enough slack in emergency brake cable. Second the brake pads fit excessively tight in caliper bracket causing pads to not release. I had to take a little material off caliper bracket to allow pads to move freely and release.

Then once all dragging issues resolved had to rough up rotors and pads to remove glaze that was caused by dragging brakes. After all that fumbling around trial and error head scratching got them all straightened out....

 

[bbab3]

Just to update the rear calipers are the problem. I have new ones on order. Thanks for the help it really saved me some time and I appreciate it!