MISS4X4

I did the 2000 WJ booster/mc grade to my 89 xj and have been having serious issues. I got a brand new booster, but the mc I got from the junkyard since it is pretty expensive and difficult to find one new with the reservoir. Since then the front brakes have been sticking and causing the rotors to overheat and warp. I decided that I might as well buy the new MC and use the bottle off the junkyard one since I found out that the rubber seals inside the MC can swell and cause the fluid to not return to the MC from the lines. That did not help. I know that the brakes are pretty much constantly touching the rotors but after installing the new MC, new rotors, new calipers and pads I noticed a metallic scraping noise while cruising at 20 mph. Just recently I was driving up a hill on the freeway and it started to slow down as if I was pressing the gas and the brake at the same time. The brakes seemed to seize up and the rotors started smoking so I pulled over. The wheels weren't very hot but the rotors had a blue heat mark down the center of one and the other side was more or less all multicolored.

I did some more research on the braking system and I figured out that maybe the booster rod was sticking out too far and pushing on the MC when I tightened it on for installation so there was too much pressure from the start (even though the brakes felt normal) and maybe when the rpms increased while I gave it more gas the vacuum in the booster also increased, causing it to brake on it's own.

All the soft brake hoses have been replaced and the rear brakes are not having any trouble. I've triple checked all upgrade procedures and don't think I am missing anything. The only thing I have not replaced is the Proportioning Valve, I'm not sure if the valve matters as much since most of what I read says that it pertains to the rear brakes, not the front.

ANY HELP WOULD BE MOST APPRECIATED!

Too much time and money has gone into this stupid problem, I just lifted my Jeep and I can't even make it out to the desert

Firestorm500

Rotors are ruined.

Sounds like your calipers are not pulling off enough. Could be pistons frozen in bore. Were they remans or brand new?

You've probably cooked the grease in the front hubs too.

Since you replaced the brake pads, are they the right ones? Not too thick? Are they seated in their keepers properly?

I hope you didn't get your parts at AutoZone.

The brake booster only reduces pedal effort; it's not going to self-apply. In addition, as you call for more power from the engine, manifold vacuum drops until RPMs stabilize. Then vacuum reaches a new steady reading.

Turbo X_J

You must have pedal free play of 1/8 - 1/4". Without it you will block the return/fill port on the M/C, the brake fluid will heat up with usage and expand. With no where else to go since it can't flow back into the M/C it will apply pressure to the caliper pistons. At the minimum you need new rotors, and your lucky if they got that warm you didn't lose a tire as well.

MISS4X4

They calipers are supposed to be new, i bought them online but when I got them they were cardone brand. I did get the pads at autozone, they are pretty thick but they are supposedly the right ones. Do you by chance know how thick they are supposed to be? I'm starting to think it's the calipers...even if they are new. I'll take it apart today and see if I can play with the pistons.

When I tried to seat the mc on the booster it would not seat flush until i threaded the nuts on. Do you think maybe the rod being too long could be a culprit?

MISS4X4

Well I don't have much play in the pedal since I did the upgrade...but I got the 2000 wj booster (at least that's what I ordered and it looks like the right one) so that the rod wasn't too long. wtf. Do you know how I can fix this??

thakmfb

have you compared the rod from your old brake booster to the new one? I agree that if the rod is too long it is going to apply unwanted brake pressure. I would start here

MISS4X4

Well so far my brake issue has been fixed. I removed a little extension that was on the booster rod since it wouldn't seat properly, now it seats fine. I also had Napa turn the brand new rotors since they were too thick for some dumb reason.

So far this is working. Knock on wood.