Rear end bucking during 1st & 2nd gear crawling

[Hypoid]

:anon: Two words: axle wrap.

Park the Jeep on level ground, transmission in 1st or Reverse (Park if it's an auto.), NO PARKING BRAKE. Put your hands on a tire, roll the tire back and forth. It won't go far, but it will build momentum as the suspension loads and unloads. As the suspension loads and unloads, you will hear things. If you can lie under the Jeep, and roll the tire with your foot, you can watch things move...

 

[8Mud]

:anon: Two words: axle wrap.

Park the Jeep on level ground, transmission in 1st or Reverse (Park if it's an auto.), NO PARKING BRAKE. Put your hands on a tire, roll the tire back and forth. It won't go far, but it will build momentum as the suspension loads and unloads. As the suspension loads and unloads, you will hear things. If you can lie under the Jeep, and roll the tire with your foot, you can watch things move...

Just last month a buddy came by, he was leaning on the back of his XJ and we were BS ing. I hear a clunk, clunk and asked what is that? I got on my knees (which is a slow and complicated process, I'm old as dirt) and started looking around, grabbing stuff and shaking, shocks, spring ends etc. I was looking for a bad shock or maybe a bad shock bushing because that is what it sounded like. One of the U bolts holding the rear end to the springs had stretched, the axle/differential was rocking on the spring.

Maybe ease up to a curb (perpendicular) and watch the rear part of the leaf as somebody bounces the front tires off the curb, it may be hard to get a decent view of the front part of the spring. Maybe climb the curb a few times and see what the springs do. The front of the differential will want to go down the rear up, usually this is minimal, maybe a combination of weak springs and bad shocks are causing your issue. It doesn't have to be a single part causing the issues, it may be a combination of things that add up.

After looking inside the differential, at least now you are fairly confident the high cost insides of your differential appear to be in good shape and aren't getting ready to explode. If you haven't put the cover back on yet, try to find a parking spot that takes the stress off of the drive shaft (so you can turn it a little by hand left and right) and pry on the base of the spider gears with a screw driver and see how much movement you get. It may just be the angel of the photograph, but something doesn't look right with your thrust washers. And the spider gears look a little rounded on the outside edges and not crisp and sharp. May be just normal wear and tear and not a real issue and/or just the angle (and lighting) of the photo. Did you check the oil you emptied out for metal? I usually run mine through a filter to see what is in it and/or run a magnet through the bottom of the catch pan.

You may have to jack the rear off the ground, push the tire and axle in to get a little play on the C clips and then pry behind the spider gears to see how sloppy they are, you may be able to do it on the ground.

 

[8Mud]

I had that bassackwards. if you drive up onto the curb, the front of the differential will want to go up, the back down. I got distracted when I posted last, the dogs were going nuts for some reason. Well anyway the front of the differential is going to want to move, the rear springs are going to flex, how much is too much is kind of a relative thing, if it is excessive you should notice.

I haul a heavy trailer fairly often, my springs are past being flat and arch down, I never noticed any excessive spring wrap, but I have an automatic and some stiff Koni (red) shocks.