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1991 XJ Rear brakes

K

Kevinma255

NAXJA Forum User
Location
West Milford, nj
I have a 91 XJ 4.0 auto... I got not too long ago so I would not have to use my saturn in the bad weather. New exhause, shocks, bit of a spring makeover (put the main leaf from a 3in lift pack in the stock pack). through a set of 31s from a friend on it and it should be good to go. should be I say because durring the first snow storm i tapped the brakes, the fronts locked and the rears did nothing. bounced it off a guard rail. not major damage so I got it home, rebuild the rear brakes and they seemed ok for about 2 miles. just finnished redoing the rears with all new parts. new hardware, adjusters, shoes and drums.

adjusted them tight then backed off by less than a full turn. backed it down the driveway and I have the same problem. I know the brakes are applying but there is very little presure to the wheels.

think all that is left is to upgrade the master and booster to one from a newer XJ and replace the one rubber line between the body and the axle.

any other ideas would be apreciated because I am sick of keeping my jeep in for the bad weather and making my little car of plastic hanle the snow.
 
Have you replaced the rubber hoses? How are the tires?
 
did you bleed them?

If anything bleeding them will let you see what kind of flow you're getting. It's possible the rear soft line is swelled up inside and you're just not getting enough fluid.
 
Rubber line had no effect.

What master/booster combos can I swap in with minnimal modification that will give me the extra braking? 95+ will the setup from a grand swap in? I know I will have to modify the bar to the brake pedal on just about anything.
 
Did you bleed the brakes after the soft line? There is no reason you shuoldn't have sufficient stopping power with the stock system if your tires are ok, your front brakes are good, and you have all new rears.

First thing I would do is bleed all 4 wheels RR RL FR FL in sequence, flushing all the old stuff out.

How does your pedal feel? Is you brake light on continuosly?
 
There are 2 soft lines at the front... not sure if you replaced them already? Each goes from the caliper to the frame in the wheel well.

What bdahlg said is also good advice.
 
Front brakes work properly. The brakes have been bleed all the way through untill I had no air and clean fluid coming out the wheel cylinder. bled in propper order from closest to the master to the farthest. There is good flow to all the wheels, and there are no vacum leaks.

I had a simmilar problem on my 89 but that is an off-roader that travels by trailer so I just threw a master from a 98 in it and did not worry about the exactnes of the fit. I need the 91 to be reliable and close to well ballanced.
 
The fact that the fronts locked when you tapped the brakes makes me think the hoses may be deteriorating inside and acting as 1 way valves. I could be wrong though.

As for the rears not getting anything... that's odd. I hate drum brakes with a passion, messing with the springs and adjusters and crap frustrates me.
 
I might not of been clear. the problem occurs on slick (snow covered roads) on dry roads the brakes just feel weak but the fronts do not try to lock unless I try to put the pedal through the floor.
 
Did you bench bleed the master cylinder?

You're bleeding in the exact opposite in which you're supposed to. The farthest away from the master cylinder to the closest is correct (read my last post)

Bench bleed, bleed in the correct order, post up.

Are you sure you intalled the rears correctly? Not hard to screw them up.

Again, there is no reason you shouldn't have sufficient braking power with the stock system, I've done more full brake jobs; new hardlines, soft lines, everything, than I can count on a multitude of Jeeps. They all stop on a dime and work properly.
 
If everything's flowing fresh fluid and no air, all parts in the rear are new, and they're adjusted properly, you should have as well balanced brakes as they were designed to be (approx. 75% front and 25% rear)

The only other thing I can think of that might give you early front lock up or insufficient rear pressure is the proportioning/distribution block or a failed master cylinder.
 
Kevinma255 said:
...unless I try to put the pedal through the floor.
Click to expand...

Bleed in the correct order. A soft brake pedal in which you are describing means you have air in the system. Re-bleed in the correct order
 
I will try to swap the dist block before I go crazy with the master but I am leaning towards either a weak master or booster.

I apreciate the help and sugestions.

I am 34, been working on cars and trucks my entire life, have built a couple ftom the frame up and, other than my dads tractor trailer, none have frustrated me more than the jeeps. I am including a couple of fords in that list so that says something about the level of frustration I am dealing with right now.

bdahlg, are you sure on the bleed order? I have always done closest to farthest.
 
Kevinma255 said:
bdahlg, are you sure on the bleed order? I have always done closest to farthest.
Click to expand...

Yep. The idea is to get all the air out of all the lines, hence the farthest first, then working your way back up to the shortest line, then all the air will get out.

x2 on the prop valve, although if it was stuck/not working it would show the BRAKE light on the dash (or maybe thats when it's low pressure?)

I would check it anyway
 
the light will show if you have a pressure drop on one side of the system or the other-- it's just got a small metal ball (I think) that will remain centered with correct pressures. Lose pressure on one side or the other, and it gets pushed by the pressure on the other side and completes the circuit for the brake light.

Crud build-up could be keeping it from moving or restricting sufficient fluid into the rear line to allow the rears to overcome the springs quickly enough to get rear brakes.

I've never actually had one fail, but when out of other ideas I'm willing to believe it could happen.
 
Are the wheel cylinders functioning ok? They may have a small leak in them. They're cheap enough to just replace both IMO.

But you would have noticed when you had replaced the shoes....:doh: sorry wasn't thinking
 
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