Frustrating brake problem. FIXED!

[Scrapper_MV]

My brakes are still building hydraulic pressure when I drive. I have checked the M/C for risidual valves, there was none. I have replaced all of the soft lines, and the hard lines appear to be in good shape. Today I cut out the inner fender on the drivers side and moved the hard lines away from the header, that didn't help either.

This is a disc/disc set up with the original 1973 manual M/C. The brakes work good for a few miles and then they begin to apply them selves and I have to stop and open up a bleeder to release the pressure.

This problem has me stumped and very frustrated!

It was the M/C. And I put a stock unit back in. Yeah!

 

[garberz]

So somehow your booster is applying pressure to the MC? Do you have a Vac booster or a hydroboost? Or is it no power?

 

[Scrapper_MV]

So somehow your booster is applying pressure to the MC? Do you have a Vac booster or a hydroboost? Or is it no power?

No booster of any kind, the brakes are manual.

 

[GubNi]

Bad calipers. Next time it happens test them one at a time. You might try to see if the problem is time or miles. Let it idol for 15 minutes and see if you have the same problem.

 

[Scrapper_MV]

Bad calipers. Next time it happens test them one at a time. You might try to see if the problem is time or miles. Let it idol for 15 minutes and see if you have the same problem.

That's a bummer, the front calipers are 4 piston Wilwood units. I don't even want to know how much those are gonna cost!

 

[DonsBolt]

Hve you called Wilwood and asked them whats going on?? Maybe there calipers require a different master cylinder.

Also are the bleaders facing up??????

 

[Scrapper_MV]

Hve you called Wilwood and asked them whats going on?? Maybe there calipers require a different master cylinder.

Also are the bleaders facing up??????

The calipers have one bleeder screw for each piston, four in total. I bled them using the two that point up per Wilwoods website. I'll give them a call Monday. But why would they work well for a few miles, and then start applying them selves?

 

[DonsBolt]

I have no idea, thats why I figured give them a call.

 

[Broncobowsher]

Drive it, when it happens crack the brake line at the master cylinder. Do the brakes release? If so then it is the master cylinder.

Still on, try the next fitting down the line, and so on. Start at the master cylinder and work toward the caliper.

Hint, sometimes lines (particularly rubber) can get some junk in them that will act like a check valve, allowing pressure to build.

 

[Scrapper_MV]

Drive it, when it happens crack the brake line at the master cylinder. Do the brakes release? If so then it is the master cylinder.

Still on, try the next fitting down the line, and so on. Start at the master cylinder and work toward the caliper.

Hint, sometimes lines (particularly rubber) can get some junk in them that will act like a check valve, allowing pressure to build.

Thanks, I'll try that tomorrow.

 

[Wyldebill]

Make sure there is a little slack in the push rod to the MC to make sure it is returning all the way.

 

[mattt]

I'm not sure which Wilwood calipers you have, but I had a similar experience with Wilwoods on a VW once. I learned they get very finicky about the slides being lubricated that allows the caliper to float. Any length of time(6 months maybe) even if it wasn't driven, would have this happening again. So, if yours are floating calipers make sure they are floating easily, very easily, or they may be sticking which could lead to a partial sticking of the brakes.

 

[Pedestrian]

Flush the system, I have had bits of rubber/ rust that blocked the return hole of the master cylinder and kept the brakes from releasing. once the brakes start dragging, they build heat and pressure rapidly.

 

[Scrapper_MV]

I'm not sure which Wilwood calipers you have, but I had a similar experience with Wilwoods on a VW once. I learned they get very finicky about the slides being lubricated that allows the caliper to float. Any length of time(6 months maybe) even if it wasn't driven, would have this happening again. So, if yours are floating calipers make sure they are floating easily, very easily, or they may be sticking which could lead to a partial sticking of the brakes.

The calipers are not full floaters, but this Bronco did sit for years before I bought it, and the bolts on the calipers are rusty. I'll clean them up and see if that helps.

 

[Scrapper_MV]

Flush the system, I have had bits of rubber/ rust that blocked the return hole of the master cylinder and kept the brakes from releasing. once the brakes start dragging, they build heat and pressure rapidly.

This may sound stupid, but how do I flush the brake system at home? Or should I take it to a shop and have it done?

 

[Broncobowsher]

This may sound stupid, but how do I flush the brake system at home? Or should I take it to a shop and have it done?

Bleed the brakes until the fluid comes out clean.

 

[Scrapper_MV]

Bleed the brakes until the fluid comes out clean.

OK, thats easy, no power tools needed! But I have bled these things three times now, and the last time the fluid was coming out very clean.

What about the h-block, should I ditch it and put a proportioning valve there? I don't have a brake warning light in the dash anymore.

 

[ken75ranger]

I'd take bypass the H block to test the system.

 

[Scrapper_MV]

Wilwood was very lttle help. They told me to check the push rod legnth at the M/C, which I did and it seems to be right. Then they said to replace the M/C.

 

[Scrapper_MV]

Woohoo I fixed it!