Brake Issues

[Slangy]

I have been battling weak brakes for a while. The pedal has pressure to it but it is kind of soft. The Jeep will stop but I cannot lock them up. When driving off a ledge or off of my trailer, once I get to a certain point the brakes will not hold and I fall to the ground. I have new rotors, pads, drums in the rear. I flushed the old fluid and put in new fluid and bleed everything real good. Still when it is on the lift if I push in the brakes I can still rotate the front tires. This all started happening after I swapped the engine and put the master cylinder and everything back together. I thought it was just the auto transmission but last night I noticed that I could rotate the tires with the brakes applied. So I took it to the shop this morning and they said all looks good but they think my master cylinder is bad and maybe the proportioning valve. I don't think it is the proportioning valve so I am going to replace the master cylinder.

If any of you had a master go out what were some of the symptoms. Does my situation sound like a bad Master. I hate to spend the time and money doing it tonight if that's not the problem. I guess I need to stop procrastinating, we are leaving to EJS in the morning and I would like to fix it in my garage instead of on the red dirt.

Thank you

 

[DaveB]

I have had similar issues when I have let the brake fluid out of either the front or back but not both. In this case the proportioning valve shifts to only apply fluid to one circuit. I have found that if I release the pressure on the front or rear that didn't lose fluid that the valve will shift back to allow fluid to both circuits.

 

[UNSTUCK]

Does the pedal go slowly to the floor or does it stay hi and firm? Can you bypass the prop valve and test it? Are the rear tires locking up? Is the reservoir full? No leaks in the lines or at the calipers?

Usually a bad MC will allow fluid to bypass the seals, causing the pedal to go to the floor slowly. That's the easiest way to know it's gone bad. After that I would check for external leaks throughout the system. I haven't seen a prop valve fail and block fluid flow. I'm sure it happens, I just haven't seen it.

 

[benjy]

Dumb oversight, but when I switched to an auto I realized my vacuum line to the brake booster had not been connected for years.

 

[Slangy]

I have had similar issues when I have let the brake fluid out of either the front or back but not both. In this case the proportioning valve shifts to only apply fluid to one circuit. I have found that if I release the pressure on the front or rear that didn't lose fluid that the valve will shift back to allow fluid to both circuits.

I have completely flushed and bleed the system, so I think I should be good, but who the hell knows, anytime your battling time things seem to get tougher to diagnose.

Does the pedal go slowly to the floor or does it stay hi and firm? Can you bypass the prop valve and test it? Are the rear tires locking up? Is the reservoir full? No leaks in the lines or at the calipers?

Usually a bad MC will allow fluid to bypass the seals, causing the pedal to go to the floor slowly. That's the easiest way to know it's gone bad. After that I would check for external leaks throughout the system. I haven't seen a prop valve fail and block fluid flow. I'm sure it happens, I just haven't seen it.

I just went into the parking lot and turned the jeep on, placed my foot on the pedal and it slowly (real slowly) makes it's way to the floor, well not actually the floor but as far in as the pedal and everything will allow.

Dumb oversight, but when I switched to an auto I realized my vacuum line to the brake booster had not been connected for years.

That's funny because last night as I was trying to figure this all out I double checked to make sure that it was all hooked up. I got a little hopeful thinking, oh maybe if I adjust this line it will work....Nope


I am going to buy a new MC after work and try to get it solved. Building a house and a Jeep at the same time and trying to get to EJS is a real big PITA

 

[Jinx]

I am going to buy a new MC after work and try to get it solved. Building a house and a Jeep at the same time and trying to get to EJS is a real big PITA

One thing I learn the hard way was not bench bleeding the new MC good enough at first. It should come with instructions, but with no brake booster and stock CJ master cylinder I can stop my 40"s after a good gravity bleed...

Good luck I just got home from EJS Great times.