XJ Brake Booster

cherokee_kid_03

cherokee_kid_03

Rock Corps 4x4
Joined
Sep 21, 2009
Location
Marion, NC
I have a 1997 XJ and I believe that my brake booster has went out. I still have brakes but not very good. I have heard that a brake booster from a ZJ will improve my brakes and last longer than the stock XJ booster. . .Anyone done this?
 
ANYONE. . .
 
Have you disabled your booster to make sure that it is bad, you didn't sound very sure that it was bad? Would be a very quick check, but it would keep you from throwing parts at the wrong thing.
 
I'm running 34" tires with discs all the way around on the stock 1991 master cylinder and booster. I did do the proportioning valve mod to allow more pressure to the rear brakes. Your booster and master cylinder are even better than mine. Dual diaphragm booster in the 96+ I believe.

Is your pedal hard as a rock? Do you have any vacuum loss or is your engine idling high? If your pedal is still mushy then your booster is probably okay. Disable your booster and make sure that's your problem. Should only need to disconnect the vacuum hose and then apply brake pressure. Pedal should get hard as a rock and engine should idle up. If all that checks out okay bleed your brakes thoroughly to see if it helps. You may have a leak somewhere you don't know about.

You can do the prop valve mod too if you like. It's quite simple. You remove the bleeder valve on the front, take out the spring and valve and remove the o-ring. Put it back in without the o-ring and tighten it back up. All done.

If you still have no brakes or weakened brakes then you problem is elsewhere. Perhaps the master cylinder is going out or you have a leak?
 
I have a 91 Cherokee. After we wheeled one weekend, Cherokee kid and myself was having the same problem ( I think ).

The pedal seems "soft" if you are trying to hold back on a steep hill, the brakes just don't hold and the pedal is mashed to the floor. One of our buddys told us he thought upgrading to ZJ booster or master cylinder ( I don't remember which ) would fix the problem.

I have checked my fluid levels and checked for leaks and all is good. It almost feels like the master cylinder might be bad.

I know sometimes old rubber lines will get soft and swell, leading to a softer pedal but I wouldn't think that would cause the trouble. I'm thinking of swaping to stainless lines anyway.
 
I have changed the master cylinder and bleed the brakes. . . just finished installing new back brakes. The pedal is not hard at all. Its the complete opposite. It goes to the floor before it stops. And holding the brake to the floor while the jeep is in drive and giving it some gas, it will not hold either. So back to the drawing board.
 
Did you bench blend the master cylinder? Check your wheel cylinders and rear shoes as well. Make sure you have good shoes. (See below) Check for leaks EVERYWHERE and for the swelling. If you disconnect your master cylinder from the booster you can pull off the rubber seal and the rod. Look down inside of it for any apparent rust. I doubt it's your booster though. I also put silicon around master cylinder and rubber seal where the two meet because I was hearing air escape from between it and the master cylinder. After doing that and the prop valve mod my pedal was back to normal. (Did this after 8.8 axle swap.)

The real problem I had with mine before the axle swap was the rear brakes on D35 were completely gone and the wheel cylinder had no more travel. I had no leaks. Check your shoes!

My thread on this issue: http://www.nc4x4.com/forums/showthread.php?t=85852
 
Thanks for all the info. I disconnected the vac line from the booster and the engine idled up and the brake pedal was rock hard. I may bleed them again tomorrow. Anyone want to help pumping brakes tomorrow:lol:
 
Man I'd sure come and help if you were closer. I know how frustrating it was for me trying to get the brakes fixed. Best of luck to you!
 
I'll help ya, I get off work round 3:30 or 4:00 give me a call
 
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