Brake problem - Front Caliper staying locked down

[gator-n-buck]

Long story short, replaced Brake hoses, brake lines, Master Cylinder, Power Brake Booster, Back drum brakes, front rotors, calipers, and front brake pads. The only thing we didn't change was the original Proportional Valve in the 77. Double checked with the Bronco company that I purchased the lines, Booster, and Master Cylinder from and it's all correct for the 77 with disc brakes in the front and drums in the back.

Not sure why the front calipers want to stay locked down and not release? I'm guessing maybe the Proportional Valve but it worked fine before buying the new parts.

Anybody experience this or any thoughts, Thanks

 

[B RON CO]

Hi, I would double check the push rod length in the booster to master and pedal to booster. One or both may be too long. I have seen the "correct" parts come with different length shafts than we started with. If you loosen the nuts holding the master to the booster you can see if the calipers loosen up. Good luck

 

[Apogee]

You need to determine first whether it's hydraulic or mechanical. Get them to "lock", then crack the bleeder screw on the caliper. If they release, then it's a residual pressure issue. If not, then it's most likely a mechanical issue with either the piston/seals or the caliper body and slides.

 

[gator-n-buck]

You need to determine first whether it's hydraulic or mechanical. Get them to "lock", then crack the bleeder screw on the caliper. If they release, then it's a residual pressure issue. If not, then it's most likely a mechanical issue with either the piston/seals or the caliper body and slides.

Did it with the original Calipers and that's why we changed them. Will check the other issue, thanks.

 

[gator-n-buck]

Hi, I would double check the push rod length in the booster to master and pedal to booster. One or both may be too long. I have seen the "correct" parts come with different length shafts than we started with. If you loosen the nuts holding the master to the booster you can see if the calipers loosen up. Good luck

Will check and thanks

 

[DirtDonk]

Yep, what they said. Good stuff to check.
Easy to get the little clips and retainers installed incorrectly, which might jam up a caliper. But since it did it before the swap, look at the sliding surfaces to make sure they're clean, straight, smooth and lubricated.

If a little dry or rusty, use a file to clean and smooth them down. Lube with appropriate grease (I use anti-seize, but brake grease is what is made for this) and make sure things slide freely.

If you installed the little crazy shaped anti-rattle clips, make sure they're on as specified. They only work one way.

It's even easier (and way more common) to get the wrong rod length adjustment between the booster and master. There should be no more than 1/64" gap between the back of the master's piston and the tip of the rod. And no less than that too, if you can get it right on.
Much more of a gap and the pedal travel is too far.
Much less and you risk having the hydraulic pressure either not release properly, or worse still, build up until the brakes actually lock up.

Easy enough to check though. You can even leave the fluid lines connected while you remove the two nuts that retain the master to the booster. Pull it away and either use some method of gauging the depth, or just adjust the rod out until it hits the piston just before the master seats up against the booster face. Then adjust it back down just enough so that the master seats up against the booster before the rod touches down.

Paul

 

[rubbman]

Isn't there a little doodad in a new mater cylinder that keeps a minor amount of line pressure? When I installed one on my buggie I removed it before installing my brake lines.

 

[thegreatjustino]

Isn't there a little doodad in a new mater cylinder that keeps a minor amount of line pressure? When I installed one on my buggie I removed it before installing my brake lines.

If he was working on an earlier Bronco that originally came with four wheel drum brakes, this could be the case. If he in fact does have a correct '77 master cylinder, that would be front disc/rear drum and shouldn't have the residual valve in the front port. Still an idea to check though, just to be sure.

 

[gator-n-buck]

If he was working on an earlier Bronco that originally came with four wheel drum brakes, this could be the case. If he in fact does have a correct '77 master cylinder, that would be front disc/rear drum and shouldn't have the residual valve in the front port. Still an idea to check though, just to be sure.

It's a correct 77, front disc and rear drum. I purchased the 1977 booster and matching master cylinder from WildHorse.

 

[thegreatjustino]

Doesn't mean it was manufactured correctly.

 

[Rustytruck]

Do you have the largest resivour of the master cylinder hooked up to the front brakes?

 

[DirtDonk]

Most masters of modern manufacture no longer come with residual pressure check valves installed. Probably just a money saving idea on their part, but it's something we've been noticing over the last 20 years or so.
They do make valves even for disc brakes (2psi rated) as well as drum (10psi rated) but most vehicles don't even need them.
Their primary purpose was to keep fluid from bleeding back in to the reservoir on vehicles where the master cylinder was mounted low. Sometimes actually beneath the level of the brake cylinders on old trucks and cars. In those cases it was a mandatory safety item. With most modern vehicles having masters mounted well above the level of the brakes, it sort of became a non-issue.
I have seen them on some early models with anti-lock systems I think. Probably a safety measure as they were getting used to controlling pressures in the system. But I don't see them on all in external form at least. May have some internal ones, but not sure.

So having them or not in a new master is not a deal-breaker and doesn't effect proper braking.
Keeping a 10psi valve in an older master cylinder with a swapped in disc setup though, can lead to pads dragging on the rotors.
That seems to be about the only aspect to worry about these days.

Paul

 

[Timmy390]

Did the setup come with an adjustable brake rod? Sounds like the rod is too long or adjusted to be too long and not releasing the M/C.

My setup came with an adjustable rod.

Tim