Brake Problems

Here's the setup of my problem. I've got disc brakes on the front and drum brakes on the back. I have now driven the jeep 3 miles after a complete resto and the front brakes have almost locked up without my foot on the brake. I got it back in the garage, put it up on stands and the front wheels are almost locked up and will not release. The back are fine. The front will not turn by hand. I do not have a proportioning valve, but I do have a disc brake M/C from Herm.

I am getting 2 different stories from well know jeep vendors(one in Washington and the other in Oregon) that sell old jeep brake stuff. One is telling me its the master cylinder thats got an internal valve that is not releasing and keeping pressure on the front lines

The other is telling me all the problems will be cured by putting in a proportioning valve.

HELP!!!!!!!

 

Have you called Herm? I'd run it by him first.

 

Now that you brought it up.....he is one of the vendors I'm getting conflicting answers from

 

Sounds like the pressure is not being released.

 

Open the bleeder valve on both calipers and release some fluid and watch for air. Do this with the wheel off and see if the caliper piston springs back and leaves clearance between pad and disk.

 

If it releases pressure, is it the residual valve on the m/c?
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Did you just convert to front disks? Or just change the master cylinder? Or both?
If you originally had drum brakes on the front, there is a residual pressure valve (close to 10 lb) in the system. It is likely located in the master cylinder. It will need to be removed for proper disk brake operation. It is also likely that you will need a 2 lb valve to keep a very small amount of pressure for the disks and/or to keep the fluid from draining back and creating an air pocket in the line(s). Make sure the disk brake line is attached to the proper side of the master cylinder.

Here is a picture of the residual valve that I removed from my master cylinder drum brake circuit when I converted to disk brakes. It is found behind the threaded port where the brake line attaches.

 

I bought a disc brake kit for a D27 from North Atlantic Offroad Supply. It included everything including brake shoes. I also bought a disc brake dual res. M/C from Herm. I talked to him and he says if I bought a disc brake M/C from him it would have the correct 2lb valve in the front tank. I bought all brand new steel lines from Carl Walck. I put all these components on the jeep, bled the lines and at that point everything worked fine. Then......there is today.
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Oh, as with the way the new brake lines were made, the front tank supplies the front brakes. That front tank has a higher volume than the rear tank
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Another thing to check is the release of the M/C push rod. Make sure it can fully retract when the brake pedal is released. If you're not sure, disconnect the push rod from the brake pedal and see if it is coming back all the way (and not holding pressure to the hydraulic system).

 

The brake pedal is all the way out and solid as a rock
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There should be a small amount of free play-------check the push rod length, and adjust as needed.

There should be a jam nut on the push rod, to keep the adjustment where you initially set it-------you might check and see if it has moved.

 

The push rod is one piece. It came off the original dual m/c. There is nothing to adjust. Everything was working fine untill I drove it. The pedal traveled and released perfectly. I only have this problem when I assume the brake fluid gets hot from operation
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Now that I've been thinking about this since yesterday, I now remember that when I put on my new body for the jeep, it didn't sit in the same spot as the old one. Everything lined up off.

I do remember when I put the body on, the brake pedal got pushed down about 1/2 inch. When I put on the draft kit, that added about another 1/4 inch. Herm told me to use the old push rod off my old dual M/C.

I think you guys may be right about the push rod. If there isn't enough free play, could that cause the fluid to not be able to expand back into the resevoir? I also noticed that once the body was on, when I moved the jeep around, the front brakes were already a little tight and hard to roll around by hand. I thought it was just from being new.

So therefore, with the simple operational heat from the brakes coupled with the pedal being slightly pushed down cause the brakes to lock up when being driven a little?

If that is something to start with, I need another push rod. Mine is one piece. Does anyone know where to get an adjustable push rod that will fit Herm's M/C with the retaining snap ring?

 

Bump

 

You can probably just remove the bolt or clevis pin, or whatever is holding the push rod to the pedal arm, and see where the rod wants to go for a release position, measure the difference and then cut it off the end that goes in the M/C.

Depending on how things are mounted, you might get away with putting spacers between the M/C and its mount also, give it more free play for the push rod.

At least remove the bolt/pin, and see if the brakes release when you do so.

 

Yes, or just unbolt the MC from the bracket and let it move forward a little if it wants to. See if that frees the brakes. There's a spring in the MC that expands the piston back to its stop, but it's weak compared to the push from the brake pedal.

 

Yep, equally viable option.

Do whichever is easier to accomplish on your rig----the objective is to allow enough free play for the piston to return fully, and unport the return flow.

Thanks for mentioning it Tim.

 

When I did my conversion I also bought a new M/C that was supposed to be for a disc set up. I removed the residual pressure valve in the M/C and installed an inline 2# valve. I thought I remember reading that since the calipers sit higher than the M/C on the frame the pressure could build up and not release.