Rear disc brake, problems

[Rick78J10]

Ok I know this topic has been covered here as I have done a search but I am still not finding what I need.

Try to be open minded too. I do have a couple of FSJ's but this is on the CJ-7 my trail jeep that I use a waggy 20 axle under the rear and a chev 44 up front all 6 bolt.
The jeep has a 258 fuel injected, 999 auto, 4:1 transfercase, 4.56 locker F & R, 36" tires

So I used A-A brackets, 91 Chev (regular duty rotors), 82 Caddy rear caliper with e-brake.
Mater Cylinder from a 69' Corvette w/ discs 1 1/8 bore, 9" dual diaphragm booster.

Lines were plumbed with an adjustable valvle to the front and straight to the rear with a 2 psi valve.

I had installed this about 6 months ago with so so results. It was better than the drums since the disc stays cleaner. But the jeep can eventually pull through the brakes at idle.

When I was in Moab I had spoke to a vendor out there and they suggested I go to a hydro boost and stock valving in the lines.
Tried that.. no real improvement.

During the change the master failed so I replaced it.

So I am going to try front calipers from 82 caddy since they take the same pad I have and will bolt on. They have a little larger piston (2.5) instead of (2 1/8) with e-brake.

I am wondering what seems to work to slow those rear tires down enough?

Is there another rotor out there that can slip on the 20 flange that is larger in diameter and can accept a larger brake pad? Such as the ones you find on the front of a waggy or j-truck?

Any other ideas are helpful too. All I'd like to do is get to going for the weekend if at all possible.

Thanks a bunch!

[ September 21, 2005, 01:10 PM: Message edited by: Rick78J10 ]

[J10Mike]

allot of the disk brake brackets i have seen out there use the same caliper as the front wags/cher/jtrucks. unless you use a 76-78 rear caddy caliper with parking brake. but, that should give you a larger brake pad. i'm putting a disk brake conversion on my rear d60 out of a j20. it usesthe same aforementioned calipers and pads. also, these are the same as the 70s and 80s chevy trucks as well.

[Rick78J10]

So is there something different between a late 70'rotor for a chev and a waggy front rotor that uses the sam caliper and pad as the chev?

[J10Mike]

the only difference that i know of is that the 3/4 ton and 1 ton trucks use a slightly larger rotor than the half ton rigs. and, it is 8 lug.
i'm not aware of any differences between the 1/2 ton chev & fsj rotors. or, any difference between the 3/4 ton and 1 ton chev and fsj rotors. if you look it up on one of the auto parts websites, you will see that they have the same part numbers for both chev and fsj.
for example, my disk brake conversion kits came with chev rotors, calipers, and pads. all are identical to the front rotors, calipers, and pads on my front d44hd.

[ September 21, 2005, 01:30 PM: Message edited by: J10Mike ]

[Crazy_Jeepman]

Sounds to me like you are cutting your pressure to the calipers to much.

Lines were plumbed with an adjustable valvle to the front

What kind of valve? Adjustable proportioning valve? even wide open they cut your pressure. I plumb my fronts straight off the M/C, no valve. Propotioning valves are to cut pressure to the back so as to help prevent lockup and bring the rear around.

and straight to the rear with a 2 psi valve

Sounds awfull low to me, and since you have no brake power at all, it is where I would rethink your system.

[incommando]

I spoke to a couple of guys who run rear discs, one the A&A way and one a kit from Steeltech, and they both run the plumbing straight to the back without the valve you mentioned.

[JeepsAndGuns]

I was thinking the same thing about the prop valve. Like CJ said, the lines should run straight to the front, no prop valve or anything. then the rear should have the adjustable prop valve.

[projo6]

use master cylinder pn 1521 (autozone '79 z28 direct bolt on for all years) with disc brakes and no adj proportioning valve and you problem is solved

[Rick78J10]

what size is the master from a '79 Z28?

[Crazy_Jeepman]

I do not see what a M/C out of a 79 Z28 is going to do for you, since it has Drums rear and Disc front brakes on it. You already have the right Master Cylinder, for Disc brake all around. I am using a master cylinder out of a 76 Cadillac Eldorado, 1 1/8" bore on that and is designed for Disc brakes front and rear. Plumbed direct to the front and Wildwood proportioning valve in line to the rear

[incommando]

I checked master cyl. use. try a '79-'80 Trans Am with 301 TURBO motor. They ran 4 whl disks.

[AMX factor]

I use the Steeltech set and run straight from the MC to the factory prop valve. It doesn't crep or lock up the rears. Haven't had a problem at all with this setup. I agree with Crazy that pressure seems a bit low.

[Rick78J10]

So here is an update.

Ended up so far with installing the oridinal disc/drum master from the cj a 1" bore.
Along with the Off-again dual diaphragm boster.

kept the factory proprtioning valve.

Brakes are much better. Good enough to wheel this weekend! This brought more pressure to the fronts and kept the rears about the same (it feels).

Will be trying a 1" bore disc disc tonight I hope.