I just got done with the latest version of my CJ7 and im having serious brake issues. Ive got No petal at all. Everythings is brand new, and i have swapped my mast cylinder 3 times but no change. If i give it 3 quick pumps i can lock all 4, but wait a secounds and there are no brakes.
Its a CJ on 60's with 4 wheel disc, rear calipers are standard GM's off a D44, Im also running 2psi residual valves on both lines off the master, and yes they are turned the right way.
All the calipers are new, as are all the lines. and the brakes are not power assisted. literally the only thing i havnt changed its the proportioning valve, im going to be bypassing it tomorrow and see what effect that has.

you guys got any ideas? The odd part is my buddys CJ is the exact same and he has no problems.

Ive just found this site and you guys seem really on the ball, any ideas will be really helpful.

could be air in the system, when bleeding make the sure the bleed screws are pointing up, on some calipers the bleed screws dont point up and all the air wont get out the caliper. you have to remove it from the mount to get it to point up while bleeding.

Ive done just as you described on the fronts since they piont straight back, the rears piont up so there was no problem there. I thought it was just air so i bled the crap out of them and then drive around for a while and then bled them again. but still its a 3 pump to lock brake.

so is it that no one has an answer or is this a stupid question?

Did you bench bleed the master cylinder?

What size bore does your MC have? I'd think you'd need at least 1.125 bore for those calipers.
In terms of trouble shooting, try eliminating the MC from the rest of the components. Cap both out lets and check for pedal feel. It should be high and like a rock. Next hook up the rear circuit to the MC. If the pedal is still high and hard, the rears are OK. Now hook up the front circuit. Pedal should now be soft and low, implying the problem is in the front circuit. Remember, the front MC piston (primary) works off the rear (secondary) MC piston. Meaning, if the rear circuit has air in it, a low, soft pedal will be felt before the rear MC piston bottoms, allowing the front piston to build pressure. Oh, and you should not be using residual valves in a disc/disc system unless your MC is mounted below your calipers. Using residual valves can/will cause pads to drag, prematurely wearing out the inside pad.

Ditch the factory prop/combo valve and get an adjustable prop valve.
Are you running manual or power brakes? Make sure the rod is adjusted correctly ( i had to shorten mine).
~Mo

Had the exact same problem on my yj with portal axles. I went to the grand marquis master cyl from napa and works great. Problem was volume of mc output. bigger brakes/ more volume requirements. Although your friends is the same mc maybe different calipers? Its worth the $30 price regardless.Its a direct bolt on except for bending the two brake lines that go from mc to prop valve. And your planning on removing that anyway.

First off, Thanks to all that have givin there input on this.

OK to run down, yes i did bench bleed the master before i put it into the jeep, and i bleed it again after it wasnt working right.

The MC is manual

My buddies Jeep is the exact same brake wise, same calipers and MC. so theoretically they should work the same.. but they dont.

I did as bubba said and pluged both and it was a solid petel, then hooked up the rears and it was solid still, but when i hooked the front up it went to shit. I tryed bypassing the prop valve, then rebled the system. but it had no effect so i hooked it back up and then i rebled the system to get rid of any air i might of got while the lines were off. Same as it was.

I dont know what the bore size is on a stock CJ MC. is the volume issue my most likly problem? could i fix this with adjustable prop vales or do i need more volume? what gets me is my buddy Jeffs jeep is the exact same and it works great.... seems mine has been cursed since the start of the build..

Once again thanks to all yall for your help

OK, your tests indicate a problem in the front ckt--that is, if the rear MC outlet goes to the front, as it normally should. Your MC appears not to have any air in it (either piston), and with the rears connected, and the fronts capped, you had solid pedal. That says all's well with the rears and the MC. As soon as you connected to the front ckt, the rear piston in the MC is confronting air or too much piston movement in the front calipers. That's where you need to focus. As far as your MC bore being too small for the calipers you are using, it seems it should be OK, if yours and your buddy's system is in fact identical. That means same year calipers, etc--not just "I've got 1/2-ton calipers, and so does he". Different year calipers with same bore can require significantly more fluid, as an example. MC bore size requirements have to do with caliper bore size and whether or not you are running mechanical or power brakes. Mechanical brakes generally use one-size smaller bore size to give the mechanical leverage necessary to apply sufficient pressure to clamp the rotor. The bigger the bore size, the lower the pressure to the calipers, given the same pedal pressure. Smaller bore size, whith all esle being equal, will require more pedal movement. In my oppinion, if your brakes will lock up before your pedal gets too low (your call!!), then the bore size is OK.
I'd suggest you check your front system for weeping at joints, air still in system, use of low-drag calipers (if you've updated your calipers/brakes to newer units), loose wheel bearings (can cause the rotors to wobble, knocking the caliper piston deeper into its bore, requireing extra volume to move it out), and ballooning or internally leaking front rubber flex lines (had a ballooning rear line that caused soft pedal and loss of braking:mad3:).

Just as bubba jeep said make sure the calipers are staying fully extened to the rotor ,check caliper bracket aligment to rotor this can cause caliper to open to much, also be sure caliper bushings are good. JT

did you check to make sure your pads are on right....i run stock 1/2 ton front calipers (chevy) on the rear of my jeep..one time in a rush to get my shit done i put the pads on wrong, ......so i had metal on metal, brakes worked not very good though, very weak pedal untill i pumped it...next day it rained and then i saw rust on my rim i thought wtf...so i checked and no shit, i had one side on wrong...maybe not your problem but i was ready to buy new master .....because i never in a million years thought i could put pads on wrong but i did and once it was on right brakes worked fine

Bubba said everything I was thinking about.

But I'll add I am running the stock MC and prop valve in my 04 Rubicon with 1 ton brakes. My peddle did change from stock, but I like it better now. Before there was little movement from rest to lock up. Now I have lots of movement before it locks. More room for 'slow down' type brakes. I'm no where near the floor. I think the TJ uses a 3/4" bore? if I remember correctly....

Bubba, My buddys brakes our the same down to the part numbers.

so in playing with the Jeep i noticed that if i pump my brakes til i get a pedal and let off for a sec there gone. But if i keep the petal about a 1/8th to a 1/4 from coming all the way back to its resting position i keep a pedal. like it stops like a dream. Somehow i lose all brake power when the pedal tops out. I played with the old master and there doesnt seem to be any adjustment in the rod, so can put a stop on my pedal or is there a proper way to do this??

Once again thanks yall.

Sounds like a faulty master cylinder...

as stated before it feels the same as the first 3 ive had but if this is the general feeling i will swap it out again...
I bet the guys at Napa are starting to hate me

Something is making it bleed off. Either air in the lines, faulty mc, loose connections, etc.

Since you have manual brakes, it takes more to actually show a leak than if you had power brakes.

Anyway you can cap off each line at the caliper in the front? That would test the lines. Then you can hook up each individually. Maybe you have a bad caliper that is bleeding off?

Swapped the master again today and its still as it was. Im pulling the front apart to do some painting before Mudstock this weekend and i will plug the fronts and see what effect that has. might have some crappy brakes this weekend.