By: Michael J. Rollins - 3/2003

XJ Cherokee Conversion to WJ Front Brakes & Steering
Part 1 - Booster/Master Cylinder

Introduction | Part 1 Booster/Master Cylinder | Part 2 Proportioning Valve | Part 3 Knuckles/Steering/Brakes

This article is the first in a series documenting how I converted my 1988 XJ Cherokee to use newer WJ Grand Cherokee steering and brake components. In this part, I replaced the old booster and master cylinder with those from a WJ Grand Cherokee.

The '00 WJ brake booster/master cylinder modification was a lot easier than installing the later style XJ setup and it was not necessary to relocate either the washer bottle or air box on the early models. I also did not have to swap out the power brake booster pedal rod.

My old single diaphragm brake booster/master cylinder was not providing enough braking power for my modified '88 XJ.		The sheet metal was bent to fit the '00 WJ brake booster.

I started by removing my old single-diaphragm power brake booster and master cylinder. I must have saved some weight in the process. The original master was chunky steel whereas the WJ one is smaller and made out of aluminum. I did some trial fitting and found out I needed to do a few of things.

The first was to slightly bend the sheet metal up just above where the brake booster mounts for clearance. Next, I needed new nuts to attach the booster because the WJ uses smaller ones. I also used a .25" spacer between the booster and firewall for better fit and more clearance. The spacer came from a used '97 XJ booster I had sitting around. Set up this way, the brake pedal will be a little lower (about the .25" spacer used) but this isn't a problem.

Compare the '88 XJ single diaphragm to the '00 WJ double diaphragm booster.	After enlarging the WJ booster pedal rod hole (right). The flat spot allows the brake light switch to function like the original. Note the .25" clearance spacer.

I took the WJ booster and drilled the pedal rod hole out (using a large Unibit step drill bit) to just under the hole size in my original booster, then hand filed it to the same size. Then I ground a flat spot at the end of the pedal rod just like the original booster. This allows me to use my original brake light switch just as it was on the original booster. Do not to take too much or too little off... this measurement needs to be just right or the brake lights will either stay on or not turn on properly. With all this done I bolted in the booster/master cylinder using the new nuts and blue Loctite. Now I had to make the brake lines from the new master cylinder to the existing proportioning valve.

The '00 WJ brake booster/master cylinder installed in my '88 XJ. Note no relocation of the air box or washer bottle is necessary. I also wired the low fluid switch on the WJ reservoir to activate the brake light if the fluid gets low.

I reused the fittings off the original brake line from the proportioning valve but it wasn't easy to find the metric fittings for the new master cylinder. Everyone had the 10mm one for the front system but no one had the 12mm for the rear system. I ended up ordering the factory WJ lines to get the fittings. I simply re-bent the lines, cut them to proper length, and double flared on the original prop valve fittings. The original brake lines use double flared ends but the WJ master uses bubble flares so I chose to keep the bubble flared end and double flare the end that goes to the existing proportioning valve.

This step of the project done. If you are not going to continue on with the next part of the swap, then now is the time to bleed the brake system. Modification of the proportioning valve is covered in the next article.

Introduction | Part 1 Booster/Master Cylinder | Part 2 Proportioning Valve | Part 3 Knuckles/Steering/Brakes