Unsolveable Jeep CJ brake problem!

Flipper

Well-Known Member
Joined
Mar 21, 2005
Location
Raleigh, NC
I have a 77 CJ4 with power brakes (disc and drum). it is all original with 11,000 miles on it. I sat up for 5-10 years before I got it. The brakes required a pump or two every time I stopped.

Then I blew out a brake line. Repaired that, bled the brakes, and stopping was the same (pump pump stop). I bled them a few more times, no change. I get very little fluid out of the back (proportioning valve shuts off flow to the back when it "detects" a leak). So I got a vacuum bleeder and bled another few quarts through it.

Bought a new master cylinder, and bench bled, repeated the process again.

The brakes still are soft and require a pump of two to work properly. I've checked for leaks, nothing so far.

Sometimes if a hit the brakes as hard as I can the pedal will give way the last 1/2" and give me decent braking.

Thoughts?
 
On CJ's you bleed the front brakes, then the rear, then the front. This is due to the way the prop valve works. try this.
 
^
Plus if it sat for 5-10 years you need to flush the entire system and get fresh fluid in there.


There are no unsolveable problems, only untried solutions.
 
Also check to be sure the rear brakes are adjusted properly.
 
Tried that, front to back front to back. Also, fluid is flushed and clean. (I've bled more than a gallon).
 
rubber lines may have softened up with age and are bulging out=loss of pedal pressure. check all the rubber lines and report back


beat me to it.

Ok Im jumping ahead in line.
If rubber lines are new/check out, you may need to check the MC, I know its "new" but Ive had a few DOAs from AA and AZ
 
Are the calipers on the right side? If they are not, it would not bleed properly. Bleeder valve should be below brake line. Just another possible solution, good luck.
 
Are the calipers on the right side? If they are not, it would not bleed properly. Bleeder valve should be below brake line. Just another possible solution, good luck.

I thought it was the other way around, so the air can escape out the bleeder valve. :confused:
 
On the proportioning valve there is a smaller valve. It is on the front end of the prop valve. It originally had a small rubber cover over it. Under the cover you will find a small stem. Some models require you to push the stem in, but most that I have seen require you to pull the stem out. It will only pull out about 1/8" or less. You need to hold the stem out (or in) while you bleed the back brakes under pressure. Three people will make this easy or you can rig up some sort of tool to hold the valve open. Even doing it this way can be a pain. Do not let the master cyl go dry while bleeding or you will have to start over. If this doesn't work, you can bleed the rear brake lines from the master cyl back. While someone holds pressure on the brake pedal, loosen the back brake incoming line to the prop valve. After no air here, go to the out going rear brake line of the prop valve and do it again. Another trick is to back off the adjusters of the back brakes so they have a little more travel while you are bleeding the wheel cylinders.
 
along with all the other stuff mentioned, also make sure you have the correct master cylinder, on the older jeeps the only difference from manual vs vacuum was the size of the bore in the master, a smaller bore being on the manual setup, larger bore on the boosted.

The pedal linkage etc would be different to account for the difference.. BUT if you had a manual (smaller) master you would likely run out of pedal before it pushed enough volume to push on the brakes...
 
Bleed lines at master cylinder

Worth a try, Have someone man the pedal. Bleed the lines at the master. Pump it up, crack one line> pedal to floor & hold>tighten line. Do both lines a few times. This helped me one time, when I had to pump pedal a few times to get a pedal. This also works if you have to loosen one of those lines for any reason.
 
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