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I recently finished doing an 8.8 SOA swap in my 1991 Jeep comanche Pioneer 4.0 manual. I need to do something about the brakes because they are seriously lacking in stopping power. Currently all I have done is eliminated the rear proportioning valve. I am going to swap in a 95/96 XJ brake booster, master cylinder and proportioning valve. My question is seeing that the 8.8 has disc brakes do I need to find a brake booster, master cylinder and prop valve from a donor vehicle that also has disk brakes or will a donor with drums work? What would be the best set up to keep the rears from locking up before the fronts under extreme braking conditions? Thanks in advance.

Hey all -- I've read so much praise here about the brake booster swap modification on the MJ, I just had to try it out. Super easy install...used a pulled 99 Grand Cherokee MC/BB on my '91 6 cyl 4.0 MJ, didn't have to fabricate the rod or anything..fit great. Now that I'm on the road and testing it out, I'd like to ask about a couple of things I've noticed: 1. I did some harder braking at semi-higher speeds in our residential neighborhood, and there is a "squeak" or whiny/airy noise that comes from what seems to be the brake booster when I brake hard at higher speeds. Any thoughts as to this? Did I get a bad/failing booster, perhaps? Everything works fine in regard to the booster otherwise. The vacuum hose is snug and in good condition. Master cylinder? Didn't see any leaking fluid around the booster, MC, line fittings, or anywhere nearby. The sound is not consistent in degree each time, nor does it happen when I brake under normal /gentler conditions. It's certainly an irritating sound when it occurs, if nothing else. 2. If, previous to this swap, my brake cylinder seals were seeping a little bit, could the stronger brake booster send enough force to damage the seals even worse, right off the bat? After driving and "hard braking" for about 10 minutes, I parked the truck and it smelled of burning rubber...a little smoke still steaming from behind the Rear driver-side wheel from all the hard braking I suppose (don't worry, this is not something I make a practice of). The rim and drum area looked shiny with fresh fluid. While the question of whether the cylinder needs to be replaced probably doesn't need to be asked, I guess I'm simply curious as to whether the stronger brake booster could "bust out" weakened brake cylinder seals? 3. My brakes seem spongier than they used to be before the swap. To be honest, I was expecting a nice tight, responsive braking feel. Instead, it feels soft...not awful, necessarily, but not quite what I was expecting based on all the other feedback I've read. I might even say "not quite as good" as it felt with the original single-diaphram setup. Acceptable, I guess..but nothing especially noteworthy. And if I apply pressure to the brake pedal when parked, it doesn't really firm up at any point but kind of slightly compresses until it is close to (but not on) the floor. Normal? I had a buddy help me a little bit with the swap. He bled the valves while I pumped the brake pedal. If I remember correctly though, he went in the order of: RL, RR, FR, FL. From what I've read in the forums, you have to go in the order of RR, RL, FR, FL. Is that correct? Why is that the case? So based on the info I've given you, does anybody have any advice or experience with any of these "issues"? I'm not exactly a mechanic, just done some basic tinkering on my own stuff now and again, so a lot of this stuff I'm still navigating for the first time. Thanks for making it through this essay, and for any thoughts you might have to offer.

I searched through 3 pages of stuff and didnt really find out what I exactly needed to know. I got a brake booster and master cylinder from a buddy that was parting out a 99 XJ. What all is entailed to swap it with the old crap in my 89?