ZJ rear discs to XJ and master cylinder

Instead of just using the ZJ porportioning valve and trying to get the bracket right, is there any reason that you can't just use the entire ZJ master cylinder assembly, valve and all?

i thought all you had to do was swap the springs inside. i'm not a 100% on that. its not to bad with out it unless I'm in rain and snow but I'm adding an adjustable pv so i can roll it to the rear a bit for towing my boat or a rear load

RedChuck said:

i thought all you had to do was swap the springs inside. i'm not a 100% on that. its not to bad with out it unless I'm in rain and snow but I'm adding an adjustable pv so i can roll it to the rear a bit for towing my boat or a rear load

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This is what I have done, as well as a few other friends of mine.

I used a WJ master, proportioning valve and booster with WJ front calipers and ZJ rear calipers... Works great. It stops a hell of a lot better than it did factory.

I did the ZJ rear disks, the internals from the ZJ proportioning valve swapped into mine (remove the bolt in the end of the proportioning valve that faces forward and swap the internals), and I have a WJ master cylinder. I think the ZJ master cylinder might give you problems when you go to connect to your brake pedal. The WJ only required a small amount of drilling and grinding on the connecting rod.

Disclaimer - I did the work to a 89 XJ, I assume you have a 99 XJ.

swapping the bracket was not that bad. I did it before I got my vise but I would imagine it would only take a few minutes with a vise.

I will be in your neck of the woods tomorrow if you are ready to do this and want help.

Josh

98GhostXJ said:

Instead of just using the ZJ porportioning valve and trying to get the bracket right, is there any reason that you can't just use the entire ZJ master cylinder assembly, valve and all?

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Assuming that your UserName identifies you are doing this modification to a '98 XJ; then you can reuse the existing master cylinder, and proportioning valve. The 1998 XJ has a dual diaphram vacuum booster which will work fine with your disc brakes.
Once you have installed the ZJ disc brake assemblies modify the proportioning valve for front and rear disc brakes. Just unscrew the nut from the front of the XJ proportioner, remove the spring and shuttle valve, remove the rubber seal from the shuttle valve and reinstall the shuttle valve and spring into the proportioning valve.
Back in 2000 I installed disc brakes on the '98 XJ Corp 8.25 and modified the proportioning valve as I outlined above. This modification provides equal pressure to the front and rear brakes. As long as you are running a lift with at least 31" tires your braking will not be too aggressive.

OK, so basically I am disabling the porportioning by removing the rubber seal and that gives me a 50/50 balance which is what you want w/ 4 wheel discs. I like it. BTW I'm lifted 4.5" with 33" tires, and yes it's a '98 with an 8.25 rear axle.

Thanks

XJensen said:

I will be in your neck of the woods tomorrow if you are ready to do this and want help.

Josh

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Thanks Josh, but I haven't even got any of the parts yet, I am just doing some prelim research, making sure I do it right when the time comes.