WJ Grand Cherokee Master Cylinder and Booster Upgrade How-To
 

I'm working on upgrading my 88 XJ's master cylinder and single diaphragm power brake booster (NON ABS) to the newer and more powerful 2002 WJ master cylinder and dual diaphragm power brake booster.

This was my original source of information - http://www.4x4wire.com/jeep/tech/bra...kes03/booster/

I think I can make a better write-up.

Tools Used - wrenches, flare nut wrenches, various sockets/ratchets/extensions, small pipe cutter, brake line double flaring tool kit

What you need is a 1999-2004 Grand Cherokee WJ master cylinder and brake booster. Save the nuts that bolt the booster to the firewall and the lines that attach the to master cylinder. You also reuse the XJ pedal and brake light switch.

I got a used 2002 master cylinder and booster for $108 from Kubis Auto Parts in Auburn, NY (you can order from them online).

Remove the old master cylinder and booster by disconnecting the lines from master cylinder and removing the four bolts inside the passenger compartment on the firewall. Unbolt the one bolt holding the pedal and disconnect the brake light switch.

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New on the left, old on the right...

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New rod you have to modify...

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Old rod...

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I used a step drill to drill out the hole in the new rod until the bushings for the pedal bolt fit securely.

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Next you have to grind the flat spot for the brake light switch. Old rod thickness measurement...

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New rod thickness measurement before grinding and after drilling...

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After grinding, an acceptable thickness IMO...

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With the brake light switch on the new rod...

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Now for the brake lines...

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For this you need a small pipe cutter and a brake line double-flaring tool kit. I got the pipe cutter at Sears and the double-flaring kit was a great deal at Advance Auto. The cutter even fits in the box with the flaring tools. There are some brake line adapters pictured but they weren't needed.

Cut the proportioning valve ends off of the lines coming from the master cylinder on both master cylinders. You're going to want to to put the nuts from the old lines onto the new lines because what will be on the WJ lines are metric and won't work with the XJ proportioning valve. So XJ nuts on the WJ lines (make sure you note the difference between front and back, and then make your double flares...

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Then bolt it in...

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It takes some creative bending of the lines to get them to work. Make sure not to bend any too much that you pinch a line. make gradual bends using a brake line bender or around pieces of pipe. Also, it is much easier to bolt the lines to the proportioning valve and then bolt them to the master cylinder since room is tight around the proportioning valve once the master cylinder and booster are in.

NOTE - Make sure to bend up the pinch seem above the booster so it clears the fender.

NOTE - Some people say you should use a 1/4" spacer between the booster and firewall for pedal position. I put some 1/8" thick washers on the bolts between the booster and firewall and the pedal position looks good to me.

NOTE - Removing the washer fluid bottle makes this easier. Three small screws and some connectors.

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This was all done in about 3 hours last night (and the only light I had was flashlight and a gas lantern). Tonight, a lot of brake bleeding...

The bleeding went well except I had to replace some clogged bleeders. The brakes are definitely better than stock. I just did a 200 miles trip with a trailer and no trouble stopping. I'm very happy with this upgrade.

1 problem though is when I put the washer bottle back, one of the washer fluid pumps is being pushed on by the brake lines. Keep that in mind when bending the brake lines.

2nd problem is that my brake light switch is taking some tweaking. I guess I removed too much material because I had to use a zip tie to lift up on the brake light switch so it would work. Every now and then I have to reach down and adjust it slightly. I'm going to work on a better fix for this once I get some time, but the brake lights do work.

Just to add there is another write-up here on NAXJA

http://www.naxja.org/forum/showthread.php?t=983426