Disc brakes won't release

FOMOCO_1546 · Sep 20, 2009

I started my bronco for the first time today after an 8 year restoration. I converted my drum brakes to discs with a 76 donor. I replaced everything that i could with new parts, booster, master cylnder, ss lines, porportioning valve, and everything new at the axle. I adjusted the push rod between the booster and mc between 7/8-15/16. The front wheels will turn ok when the engine is off, but when I start it up and have vacuum and apply the brakes, the brakes stay on. The pedal feels normal to me. Anyone have an idea what could be wrong. Thanks

broncnaz · Sep 20, 2009

Try closer to 7/8 maybe even a tad bit less and check your pushrod lenght from the pedal to the bell crank make sure its not putting pressure on the system.

Also there could be rust in the system if it has been a long time since you converted it. brake fluid attracts water. Could be the MC or calipers sticking due to rust/corrosion.

FOMOCO_1546 · Sep 20, 2009

Thanks, I adjusted the booster rod in until it wouldn't go in anymore. Same results. I had everything put together about 3yrs. ago, but never filled with fluid untill this week. I'll check the rod at the pedal.

crunch · Sep 20, 2009

If you replaced brake calipers with "plastic" piston economy rebuild type they tend to stick in the bore.

canrel · Sep 21, 2009

If you think the rod between the booster and master might be to long, back the nuts off a little so there is a little gap between them. If you have someone to help, raise the rear apply the brakes and have them try to turn the tire by hand as you loosen the master. If tire starts to turn you found it. Can do the same with the rod going into the booster from the pedal. Just a thought, Is the e-brake on? ;D

66bronco74 · Sep 21, 2009

Did you get a new MC for Disk Brakes? I believe a MC for drum brakes has a check valve that the disk brake ones dont (And would keep pressure in the lines).

Also I had a similar problem and it was the push rod from the booster to the MC being set too long.

bronco69drp · Sep 21, 2009

sometime the piston sticks in the caliper bore. pull your calipers off & press the pistons in a little(with a 'c' clamp), put them back on & you should be ok.;D

DirtDonk · Sep 21, 2009

Like 66 said, if the master is a drum brake version, the residual pressure check valve might be contributing to the issue.
Sitting for that long, the sliding surfaces on the mounts and the calipers themselves, might be rusted enough to cause the sticking.

I've used the drum master with the discs before, without any trouble, but that was with brand new and lubricated sliders, so there was no tag-teaming of things to cause any excess sticking. Changed it out, not long after though, just to make it more "correct" and so I wouldn't run into that issue inthe future.

Might just be time for a full freshening up of the brakes.

Paul

FOMOCO_1546 · Sep 21, 2009

I feel pretty dumb. My problem was the bellcrank bolt was to tight causing the brake pedal to not release. I don't have much play in the pedal before the brakes take hold. I didn't realize the pedal wasn't returning. Brakes seem to work great. Thanks

Disc brakes won't release

FOMOCO_1546

Full Member

broncnaz

Bronco Guru

FOMOCO_1546

Full Member

crunch

New Member

canrel

Jr. Member

66bronco74

Jr. Member

bronco69drp

Jr. Member

DirtDonk

Bronco Guru

FOMOCO_1546

Full Member

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