Brakes locking up & not releasing.

[kevpie]

New to this site. CJ7 Stock V8. Haveing a heck of a time with front disk brakes locking and not releasing. I replaced both calipers, hoses, bearings, and manual master cylinder (2 resevior). Bled brakes well. On jack stands now.
When I apply the brake pedal the calipers lock up but won't float correctly when releasing the pedal. The tires will not turn. Removing the metal brake line from the master cylinder will allow a pressure drop enough to let the calipers float even without tires.
Note: On wet mornings the rear drum 11" brakes grab once then seem to work fine.
Any suggestions?

 

[Torxhead]

The first thing I would check would be to make sure the brake pedal is releasing completly. Some guys will add a spring to make sure the pedal returns all the way. Other than that, I would think your issue is further up the line.

 

[Lumpy Grits]

Did this just start?
R U SURE you have a M/C for disc/shoe combo? Sounds to me like your M/C is for shoe/shoe--
Have you messed with the p'valve?
LG

 

[gutthans]

Did this just start?
R U SURE you have a M/C for disc/shoe combo? Sounds to me like your M/C is for shoe/shoe--
Have you messed with the p'valve?
LG

Also, make certain that you don't have the lines reversed at the MC. MOST disc/drum MC's will use the rear port for the front discs, and the front port for the rear drums. It's counter-intuitive, but that seems to be the arrangement for almost all dual brake MC's.

I would vote for brake pedal return spring as most likely though...

 

[jdcaples]

This is a long shot, but I have seen it before: Older rubber brake lines are able to fray internally. If they peel off from the interior wall in the correct direction, they act as a check valve, preventing fluid returning from the wheel cyl to the master cyl. This is not visible from the outside of the hose and can only be confirmed by autopsy or by sticking some pipe cleaner into the hole from the wheel cyl side of the line.

If the lines are new, it's probably not the issue. Every time I saw this, it was from decades-old rubber brake lines.

-Jon

 

[tarry99]

New to this site. CJ7 Stock V8. Haveing a heck of a time with front disk brakes locking and not releasing. I replaced both calipers, hoses, bearings, and manual master cylinder (2 resevior). Bled brakes well. On jack stands now.
When I apply the brake pedal the calipers lock up but won't float correctly when releasing the pedal. The tires will not turn. Removing the metal brake line from the master cylinder will allow a pressure drop enough to let the calipers float even without tires.
Note: On wet mornings the rear drum 11" brakes grab once then seem to work fine.
Any suggestions?

Are these factory Disc's on the front with the 11" drums on the back? Or a junkyard swap?

Disc brakes require more fluid volume than the drums.........hence the need for the front system to have a larger reservoir.......newer Master cylinders that work with Front and rear Disc have balanced reservoir's............in either case both will work...........you also need a 2 lb residual valve up front for the disc's and a 10 lb valve for the Drums.......these are check valves that hold residual pressure against the system.......if installed backwards they will not work and brakes will not release...............some Master Cylinders have the correct valves already installed as will as some Proportioning valves can be had that are also for front Disc's and rear drums that also have the correct valves built in...........you need to go back to each component and understand how each is valved........once you have the correct Items in-line the system should work correctly.