help!

I’m having problems with my brakes on my 71 CJ. I have a dual reservoir master cylinder with disks up front and drums on the rear. My problem is the front brakes start to lock up after a couple of miles, I have bled the brakes a dozen time but still have the problem. I never had a problem until I installed speed bleeders I think I never had all of the air out of the system and this is the first time they are bled correctly. I think I have it down to two things either there is a check valve in the master cylinder that’s holding pressure or it’s the heat from the headers expanding the fluid.
I need to get this fixed this weekend because I’m going up to lake alpine next weekend.

What do you think? I’m going to try a heat shield first and then maybe switch the front and back lines on the master cylinder .

Thanks for you help,
Chip.

 

Did you convert to disks ? If so, did you change, or remove, the pressure valve in the master cylinder ? I think it came stock (drums) with a 12lb residual pressure valve. This needs to be changed to a 2lb valve if you converted to disks.

 

Yes it has been converted and the master cylinder has been changed, not sure what year or model it came from. I had residual pressure valves in-line but took them out when I started to have this trouble. I have the large master cylinder reservoir going to the fronts and the small going to the rear.

Chip,

 

I'd say you need to adjust the rod between the pedal and the master cylinder. There should be some play when the pedal is released.

 

thanks for your help! it was the rod.

chip

 

Glad to hear you got the problem fixed. As a note, I've seen this same symptom when the flex brake hoses get old. The outside of the hoses can look OK, even when the centers are collapsing. The pressure from the MC is enough to push fluid across, but the return pressure isn't enough to push fluid past the obstructed hose center, so they drag or lock up.