My Cherokee needs some brake TLC, but the main issue is this. Power brakes. With the car running, the brake pedal travels nearly to the floor. I suspect the caliper pins are frozen/ corroded and not sliding. The brakes work, but the pedal travel is excessive. Second related issue, when I push on the pedal, I hear an air leak or suction sound coming from under the dash near the brake pedal arm. If I push the pedal hard and hold it, the hissing stops, but just the slightest relief of pedal pressure and the hissing returns.

With the engine off, the pedal still travels nearly to the floor and does firm up slightly with three pumps, but not like a car with power brakes usually does.

With engine off and foot holding pressure on the pedal, then start the engine, the pedal will travel down slightly, then start the hissing.

Brake fluid reservoir is full. Fluid needs to be changed, yes, but I think it is not related to the hissing and excessive pedal travel

Can anyone give a diagnosis?

 

Early model XJs, like your 87, have a single-diaphragm vacuum brake booster. In 95, it was upgraded to a dual-diaphragm; a HUGE improvement. Unfortunately you have to change the master cylinder as well.

The hardest part of the swap is the change from inverted to bubble flare at the master cylinder. I got pre-flared lengths of easy-bend tubing from the parts store, bent and cut them to the lengths I needed and had the local shop flare them fore me. If you drop if off and come back the next day, they're willing to do just about anything. If you need it on your timeline, they may not be so willing.

The easiest thing to do is get this kit: https://www.quadratec.com/p/omix-ada...ep-cherokee-xj

It's just 95-96 XJ parts w/ a 1/4" spacer at the firewall that you can see in the 1st picture between the white seal and the booster itself. If you can make that spacer or get one from a JY, you can get the parts for cheaper. Swapping in parts from a GC is also common since they're more common in the JY, but I didn't go that route, so you're better off searching on that one...

This is a cut-n-dry issue with early XJs; you won't fix it any other way...

 

Nice find. A bit cheaper on Amazon
I might go that route. I bought a GC setup from DeadJeeps, but what they finally shipped 2 months later was a piece of junk that looked nothing like the picture on their website. It was so rusty with holds in the body that it wouldn't hold vacuum. Yeah avoid deadjeep.com

 

Thanks for the replies, but what am I fixing? I know you are suggesting to replace the booster, but why? What is the diagnosis? Where might the hissing/sucking sound be coming from?

 

You're replacing the booster because it's old engineering. By replacing it with a dual-diaphragm booster you get twice, give or take, the hydraulic pressure to the calipers. It's a night and day difference, going from old 70's truck brakes to at least late 90s Jeep brakes :-)

The hissing sound is air leaking into the brake booster.

https://www.firestonecompleteautocar...-when-braking/

 

The only thing that hisses is the booster.
Not everyone has the resources in the form of tools, place to work and dollars to convert to the later booster.
If you had to replace the booster with stock, it would not signal the coming Apocolypse.

 

A rear brake adjustment raised the pedal significantly. An under dash inspection revealed worn bushing in the brake arm to booster push rod, giving even more travel of the brake pedal. I have decided the hissing is normal, as it is just air entering the atmospheric pressure side of the booster. The car stops fine with very little foot pressure, and the pedal pressure does not bleed off under constant pushing of my foot.

Thanks for all the help.