I think I have a backlash problem ...

[canyonfireguy]

1999 XJ. 3.5" lift and 31" tires, but bone stock axles. Dana 30 front, and Chrysler 8.25 rear. AX15 manual trans, so 3.07:1 gears. 133,000 miles (literally rolled 133 today). Have been hearing the "growl" from the rear end for a week or two now. Popped the diff cover off today. Oil was very glittery with very fine metal dust. What I think is my backlash is horrible. Lots of slop and pinion and ring gears are only barely contacting. Everything is tight, and no sign of adjuster lock or lock bolts loose or having moved. Teeth on gears look fine. No chipping or damage, and no indications of extreme wear. I have done a lot of wheeling and towing with this Jeep, and there has been some minor driveshaft wobble when first starting out ever since the lift was done. There does not seem to be any lateral or front to back movement in the pinion bearing, and no oil leaking out of that front seal.

Is this something that just needs to be adjusted or are my pinion and ring gears worn out at 133,000 miles? I would also love to hear some advice and recommendations on best gear ratio and LSD carrier or lockers for 31s with 33s being a possible upgrade later on. Appreciate any help offered.

 

[8Mud]

The first thing I'd do is pry up from the bottom of the ring gear and check for play in the carrier bearings. Next look closely at the spider gears, sharp edges and bright metal is good, rounded edges and black streaks in the gear teeth is bad. If you've overloaded the pinion it is possible the collapsable bushing has compressed. I check the pinion by slapping the side of the yoke hard with the palm of my hand. You can feel the click, either pinion bearings or collapsable bushing. There is a little dip inside the case very near the pinion bearing, metal flakes will collect there.
The color and the texture of the bearings tell a lot. Dark or discolored is from heat, rough surfaces mean they are close to failure, shedding metal flakes and they are shot.

 

[Ecomike]

Dude, or is it Mud? LOL, nice to see you still alive and kicking about here during the holidays. Been a long time.



My Jeep herd is multiplying.



My son married a Camanche Squaw (Jeep Truck LOL) but the Biotch did not want to leave Oregon last year (crank bearings died, oil pump pressure went to zero after just a 50 mile drive to Texas) so he had to tow the bitch home to Texas LOLOL. She is a beauty, New paint Job, no rust, 6" lift, Long bed, super rare. As perrdy as they come.



Nice to see some of us still here.... We have 6 Jeeps now, LOL. Planning to sell 1-3 next year. Getting to old (Rheumatoid Arthritis) for this shit.


Did not know you were gear head, rear end (LOL) expert too?



Carry on sir...

The first thing I'd do is pry up from the bottom of the ring gear and check for play in the carrier bearings. Next look closely at the spider gears, sharp edges and bright metal is good, rounded edges and black streaks in the gear teeth is bad. If you've overloaded the pinion it is possible the collapsable bushing has compressed. I check the pinion by slapping the side of the yoke hard with the palm of my hand. You can feel the click, either pinion bearings or collapsable bushing. There is a little dip inside the case very near the pinion bearing, metal flakes will collect there.
The color and the texture of the bearings tell a lot. Dark or discolored is from heat, rough surfaces mean they are close to failure, shedding metal flakes and they are shot.

 

[canyonfireguy]

The first thing I'd do is pry up from the bottom of the ring gear and check for play in the carrier bearings. Next look closely at the spider gears, sharp edges and bright metal is good, rounded edges and black streaks in the gear teeth is bad. If you've overloaded the pinion it is possible the collapsable bushing has compressed. I check the pinion by slapping the side of the yoke hard with the palm of my hand. You can feel the click, either pinion bearings or collapsable bushing. There is a little dip inside the case very near the pinion bearing, metal flakes will collect there.
The color and the texture of the bearings tell a lot. Dark or discolored is from heat, rough surfaces mean they are close to failure, shedding metal flakes and they are shot.

Thank you for the response and the suggestions. There are no metal flakes or large pieces in the housing at all. Only very fine dust mixed into the oil. Zero play in the ring gear, carrier, or bearings when prying up on them with a pry bar. I have hit the pinion with my palm, kicked out with a boot, and whacked it with a rubber mallet, and can detect no movement up and down or side to side. The spider gears are a little shinier and only slightly more rounded than the teeth on the ring and pinion gears, but they all look pretty good for 133,000 miles. The teeth on the ring and pinion gears are still good and square with defined edges.

I'm kind of stumped. It's almost like they built it on a Friday night and just forgot to set the backlash and it opened up more with wear until it started howling or something.

I need to regear it to 3.55 or 3.73 to push the 31s better and I would like to install an LSD or lockers in it, but now is not great timing financially, and I need her back up and running ASAP, so I'm trying to decide whether to weld up a preload adjustment tool and set the backlash, or just bite the bullet and start replacing parts.

 

[RCP Phx]

You need to measure the actual backlash and then a determination can be made.

 

[canyonfireguy]

You need to measure the actual backlash and then a determination can be made.

We'll, I don't have one of them fancy dial backlash measuring instruments, but I'd say it's about a half inch.

 

[8Mud]

Have you checked your wheel bearings for the noise? Push up on the hub, should be very little play, like in the thousandths. In and out play doesn't mean much. If your wheel bearings are worn it won't be long until the seal starts leaking.
The only way to know for sure is to do a contact patch test. This will tell you quickly if you have too much backlash. You may also want to look at your carrier-bearing adjusters. The locking tab has been known to come loose on earlier models.

 

[RCP Phx]

Pics or a video would be even better.

 

[8Mud]

Dude, or is it Mud? LOL, nice to see you still alive and kicking about here during the holidays. Been a long time.



My Jeep herd is multiplying.



My son married a Camanche Squaw (Jeep Truck LOL) but the Biotch did not want to leave Oregon last year (crank bearings died, oil pump pressure went to zero after just a 50 mile drive to Texas) so he had to tow the bitch home to Texas LOLOL. She is a beauty, New paint Job, no rust, 6" lift, Long bed, super rare. As perrdy as they come.



Nice to see some of us still here.... We have 6 Jeeps now, LOL. Planning to sell 1-3 next year. Getting to old (Rheumatoid Arthritis) for this shit.


Did not know you were gear head, rear end (LOL) expert too?



Carry on sir...

I'm still on the top side of the dirt. I'm an expert at very little, I know a little about a lot of things. Mostly from necessity, when I got my first XJ, there were no parts available I had to order everything out of the states, in fact even before that when the wife had her FSJ wagoneer. Then I found some shops willing to work on my Jeeps, but invariably I had to redo the job after I got it back from the shop. My first XJ was in 87, you don't own one that long without learning a few things. My last XJ was one the Jeep dealership gave up on and basically gave it to me.

Gear sets sound like voodoo, but so far all that I've done worked well and lasted. I must be doing something right.

My knees are shot. My days crawling around under an XJ are over with. Getting down is easy with a gravity assist, getting back up again without help or a handhold is basically impossible.

Nice hearing from you again Happy New Year and I hope Santa was good to you.

 

[8Mud]

Last thought don't be too sure that growl is coming from the rear differential, sound travels through the frame and it can fool you. I've known some really good mechanics that have been fooled following a noise to the wrong source.

 

[canyonfireguy]

Last thought don't be too sure that growl is coming from the rear differential, sound travels through the frame and it can fool you. I've known some really good mechanics that have been fooled following a noise to the wrong source.

Oh, it's from the rear diff alright. When I turn the rear driveshaft slowly, I can feel the ring and pinion gears not meshing properly due to them not being in close enough contact, and only contacting on the edges of the teeth.

I'm just trying to figure out how it could get like this of nothing is loose, and whether I should try to adjust the backlash or start replacing stuff. Thanks.

 

[8Mud]

Oh, it's from the rear diff alright. When I turn the rear driveshaft slowly, I can feel the ring and pinion gears not meshing properly due to them not being in close enough contact, and only contacting on the edges of the teeth.

I'm just trying to figure out how it could get like this of nothing is loose, and whether I should try to adjust the backlash or start replacing stuff. Thanks.

First thing is to check and see if the carrier bearing adjuster bolt has come loose and allowed the adjuster to back off.
I really can't see how the ring gear has shifted this much without a bearing failure or the adjuster coming loose. Have you tried prying the carrier left and right?
That slip catch feeling may be coming from someplace else. I do know for a fact the collapsable bushing can get compressed or stressed and can cause that slip catch feeling when the pinion flops around a little and can even make a ratcheting noise when really loose.
I had one set of spider gears that cooked. the edges of the gear were rounded and the face of the gear teeth were very discolored. I forget the proper spider gear thrust washer clearance 3.5 thousandths but don't quote me. Thrust washers wear and spiders get sloppy.
I still say to a contact test, not that hard. I use copper paste for a quick check. Not ideal but will give you a rough idea quickly. Spray everything down with brake cleaner, dry, and paint on a thin coat of copper paste with a small paintbrush. If your contact patch is way out near the edge of the gear teeth you definitely have a backlash issue. The next step would be to figure out why? Some people use toothpaste.

 

[Runnin'OnEmpty]

Toothpaste.....I'll file that away for future reference.

I once had the same symptoms show up on another vehicle.
Turned out to be the ring gear bolts had loosened up nearly
to the point of falling out. This was obvious though, when I
removed the cover.

If you really have 1/2" of play, something is very wrong.
Maybe the pinion nut has backed off...???

 

[canyonfireguy]

** UPDATE **

I think I found the culprit! While the backlash does seem a bit excessive, the grinding / growling is not coming from the meshing of the ring and pinion gears at all. I tore the whole thing down to the point where only the ring and pinion gears were left in it, and it still had the crunchy feeling when rotating the yoke, So I pulled the carrier and ring gear out and it was still doing it. The crunchiness is coming from the foremost motive bearing / race on the pinion shaft. Looks like some water got in there and rusted out the very front bearing race. Bearings have a little bit of slop, but are in relatively good shape. Spent the rest of the day calling around and no one in town has any of the parts in stock, so I am going to order them online.

Now I just have to figure out whether I am going to just replace the motive bearings and races and get her back on the road, or lower the gear ratio and install an LSD / posi in it while I am in there.

I am running 31s, but might upgrade to 33s in the future. It's a manual trans, so the current gears are 3.07:1 and I would like to get it back to feeling more like the factory gearing and get some of my low end torque back. I am also thinking that I don't want to mess with air compressors, so a passive LSD, posi, or locker would be best, or maybe electric.

Would be very grateful for any recommendations on the best gear ratio and LSD / locker assy to install. Thanks.

 

[xcm]

Ring and pinions don’t like being ran outside of their range for BL. You should replace everything inside the diff. Be on the look out for scrubbing on the gear faces, or straw coloring on the teeth.
Replacing 1 pinion bearing doesn’t usually go well, but you do you.