Rear diff clacking sound during slow speed, low load

When I picked up my XJ last summer, I would occasionally hear a clacking sound when rolling to a stop with the steering wheel turned. It would just be a couple of clacks which I attributed to excessive lash in the ring and pinion gears, however I didn't spend any time analyzing the situation because the diff was working fine, and the XJ had other more pressing issues.

This past fall, I had a shop swap the stock open rear diff for a TruTrac as well as toss in new bearings and seals. Upon driving my XJ with the TruTrac, the same clacking sound was present under the same driving scenario, and it was actually much more frequent (but still only during the single scenario of coming to a stop with the wheels turned). I attributed the increase in frequency to the TruTrac causing the ring gear to go from drive to coast contact with the pinion gear more readily. As with the stock open diff, the rear end sounds fine and drives fine under all other conditions. If fact, it was noticeably more quiet at highway speeds after the TT install, presumably due to the new bearings or better lash setting.

Before I contact the shop that did the work, I'm curious if this kind of clanking sound is common, or if it indicates a particular issue. For reference, both driveshafts are brand new Adams, the transfer case was rebuilt last fall, and the AW4 is working great.

Front axle u joints?

The sound appears to be coming from the rear of the vehicle. I had the front drive shaft off for about a month last summer, but I don't recall if there was any difference with it removed. For sure I can say right now that it isn't worse in 4FT (I have an NP242) if that has any bearing on whether it could be the axle u-joints.

Unless you have knocked half the teeth of the spider gears, u-joints are the primary suspect, this includes the D30 axleshaft u-joints. Then look at any other potential suspects such as loose exhaust, other stuff dangling near the driveshafts, drum brake issues, faulty motor/transmission mounts, loose suspension fasteners, or failed suspension bushings.

Thanks. I can say with certainty that it isn't faulty motor/tranny mounts or suspension. I've been through both of those, and they are in top shape. Nothing dangling that could be knocking. The rear brakes are in excellent condition, but at this point I can't rule out whether this is related to the rear brakes. I haven't dealt with drum brakes in 30 years. I'll have another look at the D30 axle u-joints this morning.

Um, I thought he said it sounds like the noise is coming from the rear - shouldn't he at least check the rear driveshaft ujoints too?

Driveshafts are new Adams as of last fall, but I suppose I can check the rear driveshaft u-joints.

I did listen more carefully this morning, and the clack/clunk definitely occurs as the driveline transitions back and forth between forward torque and decel torque on the driveline, so it would seem to be due to a lash/free play issue somewhere in the rear portion of the driveline.

Had a clunking in my driveline greased the rear driveshaft splines noise went away but this was the 231 t case .

maxbraketorque said:

Driveshafts are new Adams as of last fall, but I suppose I can check the rear driveshaft u-joints.

I did listen more carefully this morning, and the clack/clunk definitely occurs as the driveline transitions back and forth between forward torque and decel torque on the driveline, so it would seem to be due to a lash/free play issue somewhere in the rear portion of the driveline.

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I just rebuilt my rear diff (added a TruTrac as well) and was pretty surprised to find that the spec for ring gear backlash was only 0.005-0.008 of an inch. That is incredibly small. Easy to measure with a dial gauge but almost impossible to visualize. I could feel a slight movement of the ring gear once I had it dialed in but I couldn't really see it. Part of that might have been that the view wasn't great lying under the car but the play seemed like more of a "flex" than a "movement". I hate to say this but I would be concerned that whoever worked on that differential didn't dial it in properly. The amount of play between the ring and the pinion should be almost nothing.

maxbraketorque said:

I did listen more carefully this morning, and the clack/clunk definitely occurs as the driveline transitions back and forth between forward torque and decel torque on the driveline, so it would seem to be due to a lash/free play issue somewhere in the rear portion of the driveline.

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Not that difficult to check.

tjmotter said:

I just rebuilt my rear diff (added a TruTrac as well) and was pretty surprised to find that the spec for ring gear backlash was only 0.005-0.008 of an inch. That is incredibly small. Easy to measure with a dial gauge but almost impossible to visualize. I could feel a slight movement of the ring gear once I had it dialed in but I couldn't really see it. Part of that might have been that the view wasn't great lying under the car but the play seemed like more of a "flex" than a "movement". I hate to say this but I would be concerned that whoever worked on that differential didn't dial it in properly. The amount of play between the ring and the pinion should be almost nothing.

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Spec may be super close but my 290k xj has a crap ton of slack in both diffs and is still quiet. It's really sounds like a stereotypical u joint noise. May have been an installation error on the new driveshafts.

Also the noise when turning part still leads me to front axle u joints. Have you checked the wheel bearings and if there are front brake pad grooves?

Thanks everyone. I spent about 10 minutes underneath it yesterday, and everything looks good. In particular, I'm sure the driveshaft is correctly installed and nothing is defective on it. The pinion shaft rotational free play is much less than the front (which hasn't been rebuilt), so that suggests that the ring and pinion at the rear were aligned reasonably well when the TruTrac was installed.

Brakes front and rear are in excellent condition with plenty of wear material at both front and rear.

I'll spend some more time this weekend further looking things over, in particular I'll have a close look at the front axle u-joints.