Brake issues

[SeasToSwamps]

So I’m about to buy a Comanche, current owner says brakes are acting up. Sometimes they works sometimes it’s too the floor. Already replaced master Cylinder, also mentioned rear brakes won’t bleed. Any ideas guys? Sound like a brake line issue?

[MiNi Beast]

Lines, wheel cylinders, load level valve, hows fluid looking. 

If your going to get that MJ. Get yourself a manual,haynes/chilton, then start with one issue at a time. It'll be a great bonding experience. 

[Eagle]

2 hours ago, SeasToSwamps said:

So I’m about to buy a Comanche, current owner says brakes are acting up. Sometimes they works sometimes it’s too the floor. Already replaced master Cylinder, also mentioned rear brakes won’t bleed. Any ideas guys? Sound like a brake line issue?

 

Unless it has been removed, the MJ has a height (load) sensing proportioning valve located above the rear axle. The purpose is to reduce the braking power at the rear wheels when the truck is empty, to help alleviate the problem of rear brake lock-up causing a spin-out. There are TWO lines to the rear brakes, one for normal (proportioned) braking, the other is a bypass that sends full power to the rear brakes if the front brakes fail. One or the other of those lines often rusts out, usually where they run above the gas tank.

 

Because of the safety bypass feature, there is a special procedure needed to bleed the rear brakes. The owner probably doesn't know that. My guess is that one or both of the lines to the rear brakes is/are rusted out.