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post #1 of (permalink) Old 07-29-2002, 07:24 AM Thread Starter
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Rear Disc Brake Question

I have a question fro any of you out there that have done a rear disc conversion, first off heres a semi brief description of whats been done to mine:

* Rear disc conversion using 87 Lincoln Mark VII calipers and discs,

* Installation of rubber rear brake hoses, which meant re-plumbing hard lines from the existing hard line by the fuel tank to each caliper, fabbing brackets and installing the rubber hoses to the caliper (Don't know what hoses are off of, I went to auto parts store and spent an hour or so searching through brake hoses until I found some that met my needs)

* Removed existing proportioning valve and installed an adjustable one, which meant re-plumbing some lines. Proportioning valve is on wheel well next to (but below) the master cylinder. and I have tried adjusting it to see if that was the problem...

* I had a '79 caddy (from a caddy witth rear discs) master cylinder on it, that was suppose to provide the extra ummph req'd for rear discs, but went back to my original due to this issue, thought maybe it was the problem, but the problem still exists with the stock cylinder,,,,stock cylinder still on at this point...

Thats the jist of my rear disc the problem is that I don't have any pedal until about an inch or two before it gets to the floor. I have bled the brakes with a hand pump (at least 6 times), Pumped the brakes while someone else bled them (both with the jeep running and not running), I have gravity bled them at least twice, and maybe more I can't remember anymore...[img]images/icons/smile.gif[/img]

The Jeep will stop, but won't lock up and no matter what I do I can't get the back pressure in the pedal that should be there, I have tested the power bosster and all the linkages, all ok,,,,,,,,,

The rear calipers use the brake pads for the emergency brake and are actuated by cables and a hand brake I installed, they are semi working but need a little more adjustment.....

Ther only thing I can think of at this point is that the rear hoses I have installed are too large in diameter (they are larger, or appear to be than the steel line), and maybe my pedal is going away because of all the fluid suddenly going into a larger area and the pressure releases.....anyone else have any ideas,,,,,I'm pretty close to having this thing on the road and this is driving me crazy.....thanks

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post #2 of (permalink) Old 07-29-2002, 10:49 AM Thread Starter
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Re: Rear Disc Brake Question

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post #3 of (permalink) Old 07-29-2002, 11:29 AM
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Re: Rear Disc Brake Question

I know exactly how you feel. Your post reads just like mine from a couple of months ago. I had a hell of a time getting my 4-wheel disc setup to work. It is currently working, but not as well as I had expected. The sad thing is I really don't know why it is working. I did all of the same things you did. Bled the lines, bled them again, swapped MCs etc... I can describe my current setup and maybe it will help. I am running a '68 corvette 1-1/8" master, G. Wagoneer front calipers, Cadillac rear Edlorado calipers. I have all new lines, hoses and cables. I have a wildwood adj. prop valve for the rear. My prop valve is turned all the way out so it is basically not doing anything. The thing that got my brakes working with the current setup was swapping the lines at the master. I don't know why it helped, but it made my Scrambler driveable and I haven't messed with it since then.

I would have to say that the stock CJ master isn't going to push enough fluid for 4 wheel discs. Before I installed the Corvette master I had one from a '78 ElDorado(4discs). It also didn't work. The only suggestion I have is to simplify your system. I had too much trouble figuring out what was wrong because of all the different components. That is how I ended up with manual brakes. You can e-mail me directly if you have more questions. I know how frustrating this is. I spent nearly 2 weeks working on my brakes.

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post #4 of (permalink) Old 07-29-2002, 01:41 PM
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Re: Rear Disc Brake Question

You might try adj. the length on the rod in the M.C. Longer or shorter and see if it has any +/- effect on your brakes. I dont have 4 wheel disc, but when I switched to all 1/2 ton brakes and caddy booster, I went with a larger bore M.C. and had to play with the rod length, to get mine to work correctly, I also discontinued the use of the factory prop valve. Ran the front directly to the brakes and used an adj. valve for the rear.
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