XJ sat for 2 years now weak brakes...suggestions.

So I recently purchased an 86 XJ that has been sitting for about 2 years. Rebuilt the lower half of the engine and put her all back together and it runs great! But, the braking is weak. Really weak. I blead the entire system and it is still weak. The pedal is firm though. I don't want to replace the calipers if its the master cylinder. Don't want to replace the master if its the calipers. Any ideas? Anything I can do to test the other out, other than swapping the calipers with the ones on my 89 (if they are the same)?

Did you change the pads and shoes? Probably hard as rocks after a couple of years, and a lot cheaper and easier (you'll need 'em anyway, right) than the hydraulics.

Didn't think about that or know that. Do the pads and shoes really get hard over time?

possibly the rubber hoses dry rotted? Check and see if they bulge when someone presses the brake pedal hard.

You've got a hard pedal, that means the hydraulic portion is working correctly. Bad Calipers or dry rotted brake hoses would make the pedal spongy. You can't rule those things out, since a "Hard" brake pedal can be subjective, so it may be much harder than before, but still soft enought that you could have some caliper/hose problem.

Check the adjustment on the rear drums. If the rear drums are out of adjustment, the brake pedal will take more of a stroke to build pressure (because the all the soft pedal motion is going into extending the shoes to reach the drum surface, only when the shoes hit the drum surface does the pressure in the pedal start to build). Its called pedal height, how high up is the pedal when it starts to build pressure and make the brake bite. Poorly adjusted rear drums will have a "LOW" pedal height, i.e. you have to push the pedal down pretty far before the brake bite and start braking. Well adjusted rear drums will have a "HIGH" pedal height, i.e. you barely have to push the pedal down at all to get the brakes to bite.

As mentioned, the pads and ROTORS can be your problem. Not sure on the pads, drying out? but I'm willing to believe they can detiorate just sitting in the elements, semi-mettalic pads are called that because they have iron in them, could the iron corrode? BUT, I'm willing to bet the ROTORS were all rusted, sure the rust scrapes off as you use the brakes, but what did the rust do to the surface of the rotors, did it pit them? (sometimes the pits can be hard to see) change the hardness of the surface?

Maybe the pads need to "BED-IN" into the surface of the rotor, since it has changed from the rust that accumulated since the two years ago when the pads were last used against the surface. So maybe in a hundred miles or so, maybe the pads will bed in and braking will improved dramatically.

I'd:
1st - Adjust the rear drums, then after driving 50 miles or so with braking, go back and adjust them again, there is probably rust on the inside of the drum as well, and after the rust is scrapped off you'll need to adjust the rear drums again.

2nd - If the braking doesn't improve within a 100 miles of braking or so, enough time for the old pads to BED-IN on the changed rotor surface. I'd go and get the rotors turned and get a new set of quality pads and put them together.

I just finished getting and 89 XJ back on the road after sitting behind our stables for almost 4 years in grass taller than the jeep. It had become a home for wayward rats.

After I got the motor up and running the brakes were next.
They no longer worked. Everything was rusted and deteriorated and the lines had plenty of moisture to boot.

I ended up replacing EVERTHING but the hardlines (I flushed out).
Rotors/drums/calipers/Mater Cylinder/Soft hoses/etc.

It's a one day operation and worth the peace of mind to have a new brake system.

The next time, look into getting the rebuild kits for the calipers, drum cylinders and master cylinder. The rebuild kits are like $5-$12 and its really easy to rebuild them, if you've done some brake work before. After doing a job like that, I bet your ready.

The only problem with DIY rebuild, if is there is bad corrosion on the inside of the cylinders, where seals and/or pistons slide, unless you have a machine shop, your not going to be able to fix that. Probably best to take them apart first, if they are rebuildable, buy the kit, if not, put them back together and trade them as a core for a professional rebuild replacement.

Replace the check valve on the master cylinder. Just pull the hose off, pull the old one off and push the new one in, then push the hose back on the new one. I bought an XJ where I had to stand on the brakes to get the thing to stop. Pedal was hard as a rock. I replaced the check valve (a $10 part) and now my brakes work like new. It may save you a bunch of money. With the car having sat so long you may want to go over the entire system for safety sake though.

So after troubleshooting a little, I found that I had a vacuum leak in the system. One of the two vacuum bottles behind the front bumper had a crack that the previous owner did his best to seal up. I will know here tonight if that was my problem, but has anyone had a similar issue where a large vacuum leak caused their problem. I know I could replace everything at once, but my mind would not be at ease because I wouldn't know what actually caused the problem.

Definitely change the friction - once it's been heat-cycled, friction material that sits for an extended period can be best described as "bricks."

Check the rubber hoses (there are three - two up front, and one in the back) for dry-rot. Rub them with your thumb to be sure - if it starts flaking apart, plan on replacing them quickly!

Don't just bleed the brakes - change the fluid. Brake fluid is, as you probably know, hygroscopic - and the greater the moisture content is, the lower the boiling point will be. It will also "feel softer," and you could get air pockets in the lines from steaming.

Change the fluid in the master cylinder, CLEAN the master cylinder, and pull fluid from below until it runs "clean and clear." I do this every two years - California drivers being what they are, I find having brakes to be useful...

5-90

When I wrote that I blead the system, I meant, flushed and bleed. The hoses all do look good.

OK - just making sure. Rub the hoses with your thumb anyhow - if they start to flake or just fall apart, that's dry rot.

Change your friction linings, and clean the caliper slide rails up front very well while you're about it. I find that a light application of dry graphite on the slide pins and rails, after a thorough cleaning, is about best (the dry graphite won't collect dust and crap things up.)

Inspect the surfaces of the rotors/drums as well - have a bright light handy. This will help to point up any glazing that they may have gotten from sitting for so long and then being run again.

Check anything else out? Just making sure...

5-90

Well, it all ended up being a crack in one of the vacuum reservoirs behind the front bumper. Everything works great now.