Okay, I got my Junk back from the body shop last weekend, put it on our 4th of July parade float, drove it to the fireworks, and then the brakes started acting funny. I pulled into my driveway, then backed up and pulled up on my RTI ramp for kicks, not far, just around 700 or so, to freak my passengers (girls) the brake pedal went to the floor and I rolled back. I check the fluid which was a little low, but not much, topped it off and went on my way with everything working fine. Then I backed out of my friend's driveway and the pedal went to the floor again, the next pump it was fine. The next three or four stops were fine too, then I backed up and again, pedal to the floor, next pump it was fine, it did it again when I got back home, I checked the fluid, and it's still full. WTF!

I'm running a '95 YJ with a Dana 44 front with Chevy 1/2 ton brakes on Ford rotors, no brakes at all in the rear, and the line is looped at the axle tee, I know it's not ideal, but it stops on a dime and has been like that for over a year and doesn't leak, I'll be mounting up rear disks soon, with the same calipers and rotors I have in the front.

Bad master cylinder?

I'm thinking of running an E350 master cylinder on my stock booster if it turns out my master is bad, but will that master work well with my rear disks plan? I figure on bypassing the prop valve for the rear disks, and maybe running an adjustable valve. What about using a dual diaphram booster? Don't ZJ's have them? Will the E350 master bolt to a chevy dual booster? Or is there a better choice for masters, seems to be quite a bit of debate on this, and I'll seach more on the rear disk stuff, but I'm stumped on the freaky back-up and no brakes thing, my lines are not pinched or anything.

your MC is trying to pump fluid to your back brakes but can't. that fluid has to go somewhere, so....

I'd look to the piston in the MC for a blown seal, or if you still have a propo, you might have blown it past the valve.

I think the smartest thing to do would be to hook up the rear brakes and then replace the master cylinder.

They put rear brakes on vehicles for a reason but I am sure you know that already.

yeah, I know, it was one of those temporary situations that turned into a year of excellent brakes, but why now, why only when I back up, and if I'm going to swap to a new master, which one should I use? The rear disks are waiting for me to build my new full-floater rear axle, or I could buy the brackets for my current 9" and sell the axle for that much more....

Oh, by the way, when I say no rear brakes at all, I mean, no brakes at all, no backing plate, no drum, no rotor, nothing, just the axle flange.

Originally posted by 4Bangler
Oh, by the way, when I say no rear brakes at all, I mean, no brakes at all, no backing plate, no drum, no rotor, nothing, just the axle flange.

I'm very glad you live nowhere near me. Please give warning if you intend to come to cali to run the con- I'll be sure to keep my family off the roads.:flipoff2:

It's not as dangerous as it sounds, like I said, I've been driving it like that for a year, it stops on a dime, and no, I wouldn't run the 'con like that. It did very well last winter, even on icy roads with 3 feet of snow on them, stopping the front wheels stops the back wheels in 4wd. Ain't no hills big enough in Michigan to need big brakes, and 5.38's with a SM420 and a 10.5:1 4cyl make for good compression braking.

i too did the front brakes thing....it will stop like mad! but i have cross drilled rotors and such...my prob is now that i have rear disks my brakes suck!

o and try a new MC

Chris G.

Sounds like the master failed. A kinked line would give you peddal pressure. You'd see fluid if you lost a wheel cylendar.
Water in the break line can also cause similar issue. It compresses and works great untill it heats up and turns to a vapor - like having a big air bubble. Then cools and liquid again.

The rear breaks do <20 % of your stopping, they keep you straight durring panic stops - You hurt someone because you are driving w/o rear breaks, n the judge will say :flipoff2: "Sucks to be You!"

I think my flip-floppy suspension does more to hurt my straight line braking than not having rear brakes, but solutions to both issues are in the works. I think I'll swap on a new master and get working on my rear disk, I was hoping someone would have a good suggestion for a 4 wheel disk compatable master cylinder, I'd rather not have to run an adjustable prop valve, but since I'll be running the same calipers front and rear, I'll prolly have to.

lose the propo.
mine's been gone forever and it's been nothing but great.
SWB's are so short, you really didn't need it in the first place.

Bypass the prop valve completely? Do you think that will work with the same caliper front and rear? In theroy that would put the same amount of fluid to both front and rear circuts, and I'll be increasing the master output by swapping in a larger unit. You're running no front to rear brake bias? What are you running for brakes? Disk/Drum? Disk/Disk? Large caliper/small caliper? Small caliper/ large caliper?

Originally posted by hybrid
Water in the break line can also cause similar issue. It compresses and works great untill it heats up and turns to a vapor - like having a big air bubble. Then cools and liquid again.


yes, water is a problem when it heats up and turns to vapor, but it does not compress. Also, if your brake fluid is compressing, then it's not working great... it's just not working.

If I understand the situation, I doubt the prop has anything to do with things as it had been working with the current set up for a year.