Brakes Locking Up

69 CJ5 V6 front brakes locking up.
Loosen brake line good to go. Master and wheel cylinders 2 yrs old. Jeep Manuel says need adjust freep play min 1/2 in
Which I do not have. Rod is solid no adjustment?

 

Has it worked normally and this is new and out of the blue? or did you change something?
Which brake line are you loosening?
Is it by chance freezing cold wherever the jeep is?
What fluid are you using?

Normally i'ld suspect a bad flex line. Being as cold as it is I'm wondering if water I in your master cylinder or residual pressure valve.

If it's out in the cold, I'ld challenge you to press the pedal and get it locked up then get the master cylinder heated up with engine / exhaust heat until it acts Normal then bleed the bejesus out of it.

If it is inside nice and warm i'ld pull the valves out and see if some gunk is in em.

 

Pull the boot back on the master and see if the piston is all the way out or not. you can get more slack by unbolting it and adding washers or just cutting the rod shorter. But it sounds like your fluid is boiling. I put a heat shield between the master and exhaust pipe. Just a simple thin sheet of metal will do. I had the problem with my 2a. I could tell the piston was seizing in the bore it was a crunchy tight feeling. But i put one on my cj5 aswell because they are quite close and its not something that should get hot. you should bleed the system aswell

 

Happened several times over last couple months. New hoses and yes outside and cold using synthetic fluid.

 

Thought about shimming master with washers or cut rod. Yes could be jamming but does it with cold engine.

 

Dual MC?
You have a collapsed soft line or your MC isn't releasing pressure.
Next time it happens, crack the line at the MC. If the pressure releases there is your issue. If not, but it will release at the wheel cylinder, then the issue is between the MC and the cylinder.

If it is the MC, insure the rod isn't holding the piston in. This can include the pedal pivot jamming while braking.
Insure the piston is returning completely in the bore. If not, disassemble and inspect.
Check the bore for any buildup.
Inspect the rubber components for swelling and insure there isn't any crud in the bleed back holes.
Clean the residual valve.

 

Took off master and found light corrosion on bottom of bore. Cleaned up with 600 grit paper and ready go back together.
Now to get slop out of pedals.