Answering my own question - XJ Rear Discs

Howdy, So, what you did was swap out a rear drum setup for a rear disc setup? How is the pedal response and feel?

Spdloader

P.S. Got some things cookin' with the centers right now. More on that later.

Tell me your going to post a write up with photos, how hard was it, how long, how many beers

Mark

98 XJ

How did you address the pressure differential between the old hydraulics and the new? There is a combination valve in the system designed to limit the pressure to the rear drum brakes so they cannot lock up during a panic stop. If they do lock up, you will swap ends faster than you can blink.

The brake master cylinder also sends different volumes of fluid for drum wheel cylinders vs calipers. The, or some for sure, master also has check valves for drum brake fluid flow that can jam disk calipers 'on'.

I know 100% for sure that a master cylinder for drum brakes will 'not' work for disk brakes on a CJ7 or CJ5. It 'will' jam the calipers in an 'on' position, I have seen it happen several times with sloppy parts counter persons giving out the wrong one or the wrong one in the right box. So if your gas mileage starts to drop....

Just a heads up for you.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > A month or two ago, I asked whether stock XJ wheels would still fit if

I was wondering the same thing Mike,

I would really like to see a write up with photos.

Please give us a follow-up in a month or two after you have driven in rain and on gravel and after a couple of panic stops.

I'm surprised you didn't try to use the master cylinder as well, but i'm glad it worked out well for you.

Merrill

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I did consider taking photos as I worked, but I considered others already have done a better job than I would have. Without a doubt, the best source that I studied is Eric Zappe's book, High-Performance Jeep Cherokee XJ Builder's Guids 1984-2001". The descriptions are concise and the photos well-framed and crystal clear (ericsxj.com).

This subject is also covered extensively on the NAXJA site, including a photo essay here:

guess I should pay NAXJA dues, now... It was in Zappe's book that I realized that my stock wheels would interfere with the calipers if I used ZJ parts. Zappe's used a TeraFlex kit (with Ford Explorer rotors and TF's own backing plate assemblies). But the process is identical, save for the brake lines. I kept the Liberty's hard lines (mine are 10 years old, after all). The biggest waste of time, in a fatigued state, was not realizing that the Liberty's fittings were metric; the XJ's English. Once I flared-on new fittings, no more problem.

I also wondered about the proportioning valve. I talked with someone who did the Liberty/XJ swap about 3 years ago & he's had no problem (running 31s or 32s). The Zappe book said, "I didn't need to install a different proportioning valve or modify the master cylinder per the TeraFlex instructions". My comment: Your (or my) results may vary.

I still haven't connected the E-brake cables, but I don't expect too much of a problem.

I have been working solo (Getting grease all over the garage while my wife's been out of town - but now it's all clean for when she gets off the plane in a couple of hours.), so I've only bled the rear lines, so far. Consequently, the pedal is a little spongy - but travel is less than before the change.

There still is some snow around, so I guess I could try some panic stops, to see how it tracks. I'll let everyone know after I've driven for a longer time and in varying conditions. I may go back to the yard to pull that master cyl, just for insurance.

Jim

P.S. - Spdloader - keep me posted on your project. js

How did you address the pressure differential between the old hydraulics and the new? There is a combination valve in the system designed to limit the pressure to the rear drum brakes so they cannot lock up during a panic stop. If they do lock up, you will swap ends faster than you can blink.

The brake master cylinder also sends different volumes of fluid for drum wheel cylinders vs calipers. The, or some for sure, master also has check valves for drum brake fluid flow that can jam disk calipers 'on'.

I know 100% for sure that a master cylinder for drum brakes will 'not' work for disk brakes on a CJ7 or CJ5. It 'will' jam the calipers in an 'on' position, I have seen it happen several times with sloppy parts counter persons giving out the wrong one or the wrong one in the right box. So if your gas mileage starts to drop....

Just a heads up for you.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: Final note:

Over the weekend, I drove up to visit my dad. Up there on the 45th parallel, the secondary roads are still completely snow packed or iced-over, which gave me several opportunities to mash on the brakes to see how the Jeep tracked. It glided completely straight on both snow and ice.

So, I do not think there's an issue with using the stock XJ master cylinder and proportioning valve with the Liberty rear discs.

If I experience anything different on dirt, sand, or dry pavement, I will post it here.

Jim

Final Post +1 to address other questions:

The pedal feel is great and the braking is much improved. My mileage was slightly over 20 mpg for the trip. This included some

4wd driving, too. js

We put an explorer 8.8 rear end, with disks in a freinds 88 YJ last year, no problem with brakes, just re-hooked and away he went.

Thanks for the follow up.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > >

There have been absolutely no problems with this conversion. Hard braking has not resulted in the XJ wanting to change ends. Still running the stock Master cyl. and proportioning valve.

Thanks for the follow up.

Have you tried it in snow yet?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Earlier in this thread, I mentioned that one weekend after making the conversion, I drove North where the secondary roads were either all ice- or snow-covered. I was able to mash the brakes several times, and the XJ tracked straight and smooth.

JS