Rt Front wheel dragging in reverse then pops

An interesting problem developed on my XJ while out wheeling this weekend, and I was hoping for some guidance.

94 XJ with an 89 XJ disco front axle swapped in (for 4.10 gears), running the 4x4 posi-lok setup to engage the CAD. No ABS.

About halfway through my wheeling day on Saturday I noticed that anytime my Jeep was put in reverse, I would get a loud POP noise from the right front after about 5-10 seconds of being in reverse. My friend who was riding with me got out and looked. He said the right front axle was dragging, then when it made the POP noise, it would rotate 1 revolution, then go back to dragging.

We tried this in 4wd, 2wd, with the CAD engaged and disengaged, pavement and dirt. Regardless of the situation, it would do this. Luckily forward was fine, so the Jeep made it home today without issue, however this problem scares the crap out of me.

Brainstorming with my group, we came up with the following possibilities:

1. Rt front brake caliper dragging
2. CAD collar is cocked, and not fully engaging or disengaging
3. Wheel bearing is going bad.
4. Broken shaft (figured that would have problems in forward)

I literally just got in the door, and haven't had a chance to open the axle up yet, but the diff fluid is full (checked sat morning before going out wheeling)

Can someone point me in the right direction of what this could be? Or am I just going to be gutting this axle (which seems to be cursed, I've had more problems since putting it in than ever before) putting in 1 piece shafts and overhauling everything?

Thanks in advance.

nobody?

crap... i dont want to have to rebuild the whole freaking axle.

I think if it was the caliper, it would happen in fwd and rev....

my guess would be unitbearing, but again..you'd think that would happen in both directions. I'm not all that familiar with how a disco axle operates....sounds like one of those things you're just gonna have to jack up and look at. Sorry dude...

I've got no problem with doing that, its more of an issue of when I can...

thank god I have another car.

Mine was clicking a bit when I installed my posi-lok on my 89, I had to adjust it a bit. Also do not forget to check your u-joints. If it still did it in 2wd I wouldn't think its the axle being that the outer axle is disengaged via the posi-lok. Id say jack her up and spin the tire in both directions then take the tire off and inspect it.

my votes on the wheel u-joints... if original from the '89 axle, thier life is up...

Jeremy89XJ said:

my votes on the wheel u-joints... if original from the '89 axle, thier life is up...

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would that only cause the problem in reverse?

if thats indeed the problem, i guess i might as well get rid of the disco feature, and go with 297x joints.

if it is the joints, then they would 'pop' when you change direction. You may hear it pop when going into reverse, and may not when going forward, depends on the forces at play.
You're gonna have to pull it apart and look regardless, this would just be my first assumption. Did you notice any minor (or major) shaking when on pavement at a reasonable speed? That would be another wheel joint symptom.

Jeremy89XJ said:

if it is the joints, then they would 'pop' when you change direction. You may hear it pop when going into reverse, and may not when going forward, depends on the forces at play.
You're gonna have to pull it apart and look regardless, this would just be my first assumption. Did you notice any minor (or major) shaking when on pavement at a reasonable speed? That would be another wheel joint symptom.

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not anymore. i've had some bad death wobble before though.

Perhaps you can jack up the front axle and see if spinning the right front tire spins the front left tire in 2wd with the CAD disconnected (Scenario A). Then try it again with the CAD engaged (Scenario B). If the left wheel spins in Scenario A or fails to spin in Scenario B, you can begin to suspec the CAD more strongly. Spin forward. Spin backwards. See what it tells you. . .

Ok, got to this this morning. Its the caliper, the top bolt that holds it to the knuckle is missing (wobbled out presumably) so the caliper is cocking back and acting like a wheel chock. The scoring on the inside of the rim confirms this.

So, I need a new bolt. However the other one has a weird design, looks kind of like a star of david, jutting out of it, sort of like a reverse torx head.

Whats this called, what size is it, and what size and thread pitch is the bolt?

Likely both on this side will be replaced with a standard type socket head.

Better to get them from a pick n pull. They may be a special bolt that is hardened and stepped as the ones on my car are. I had to special order the ones on the car. Your Jeep is old like mine so most of that stuff is pick n pull stuff b/c the dealers don't carry much XJ stuff anymore at least not around here.

they are 12pt heads(5/16ths i think). the closed end on most wrenches are 12pt and will work, or use a 12pt socket. i would think a parts store would be able to get a replacement(either 12pt or regular), just take the other bolt and bring it in with you.....or get one from the bone yard.

90Blue_XJ said:

Better to get them from a pick n pull. They may be a special bolt that is hardened and stepped as the ones on my car are. I had to special order the ones on the car. Your Jeep is old like mine so most of that stuff is pick n pull stuff b/c the dealers don't carry much XJ stuff anymore at least not around here.

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I replaced it with an 8.8 grade hex headed bolt from napa. The boneyard is far away and its too hot out. I'm not wheeling for a few months as I'll be gone for work, so I can do that later. At least for now I can drive it.