I heard that the newer XJ's used a dual diaphragm booster. I hoped that putting one in would increase the braking power on mine since with the 33's, I could not lock the brakes up any more.

I bought a remanufactured booster for a '96 XJ (the last year before the body changes) and a new Master Cylinder. I got the new Master because it came with the fluid reservoir, the newer style uses a separate reservoir, unlike the one in my '91. The parts cost me $200.00 including tax.
This is not meant to be a step by step, I hope you already know how to replace a booster before you start this. If not, get a service manual and read that before you try to change what Jeep did.

This is the old booster before removal. I don't know if you can see but the fluid lines come out on the pass side on this one.
I removed the air intake to give me more room. I also moved the windshield washer res. But didn't take a picture of that.
When assembling the MC to the booster I noticed a gap between the MC and the booster. This is no good because it will cause a vacuum leak.
So I fixed the gap with a little silicone.
Here are the two boosters side by side. You can see how much bigger the new one is next to the old one. You can also see that the ports for the fluid connections are on opposite sides of the MC's.
I had a company that makes lines build me some new lines from the MC to the Proportioning valve. This was also necessary because the fittings on the two MC's are different. The new MC has metric fittings, a 10mm and a 12mm. That part cost me $37.00.
Here is the new booster in and hooked up. You can clearly see the new lines I had made for from the MC to the Prop valve.
You can also tell I moved the wash reservoir out of the way.
Here is a pic of the clips that hold the operating rod on the booster to the brake pedal. I don't know how to remove these without ruining them so I got a new one at the dealer before starting. It was $3.00.
Another note here, I had tightened all of the nuts on the booster before trying to hook up the operating rod, and I couldn't do it. So I loosed the nuts and then attached the rod with the booster in but loose. It was very easy to attach the operating rod and clip then.
Here it is with everything hooked back up
And another view.
This is how far I had to move the washer bottle to get it to fit.
Next comes bleeding. I borrowed this from a friend of mine, I have a manual vacuum pump, but this is much easier. I am now looking on E-bay for a pump like this.
OK, now for the test drive.
I can now lock the front brakes again. This was clean dry pavement from 25 MPH. The upgrade works!

OK, What all did it cost, and what did I learn
All parts were $240.00.
Besides learning about attaching the operating rod before tightening the booster down, I learned that I should have mounted the booster to the car then the MC to the booster. After my test drive all seemed OK. But the next time I went out I drove further and the brakes started dragging. The further I went the more they drug.
I needed to pull the MC off and adjust the operating rod. The MC was not releasing all the way and letting the pressure back into the reservoir. So after letting the car rest for a couple of hours, I drove it home and took the MC off and adjusted the operating rod (By the way, this is one of the warnings that come with the new booster "You may have to adjust the operating rod).
Then of course I had to re bleed the brakes.

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