2001 QX4/Pathy - rear end whine after trailing arm replace

[davidsf]

I've got a 2001 QX4 120,000 miles 4WD with LSD. It's been fairly reliable..mostly the usual sorts of problems.

However, just after I completed replacing the four rear trailing arms (bought new arms with pre-installed bushings) due to the onset of the "death wobble", I noticed a perceptible whining sound from the rear-end...at roughly 40MPH...while cruising at constant speed...with foot lightly on the accelerator. While it's possible that the whine was there all the time, I don't think so. I seems to have started immediately after I replaced the trailing arms. ???

Based only on the location and nature of the sound, it sounds to me like gear whine from the differential. It's not loud...but it's definitely there. Am wondering whether the worn trailing arm bushings allowed the rear end to be slightly out of alignment which caused the differential gears to wear abnormally? Or is it even possible that the new trailing arms are somehow causing the problem? I used a torque wrench to set the pre-load on the new bushings...but it's difficult to get a torque wrench on one of the nuts...so had to do that one by feel.

The lube in the differential has been replaced twice in the life of the vehicle. The last time, I know that the LSD additive was put in. Not sure about the first time.

Any thoughts on why this is happening now?
Thanks.

[Ozzie]

Not that it is much help, but I think you have covered the possibilities of the reason yourself there.
Maybe try backing off the pre-load a little on all of the arms, and see if that makes a difference (either better or worse)?

[Towncivilian]

Is it kind of like a constant whistling noise? I think my Pathfinder (2WD open diff) has always made such a noise at around 40mph since new.

[davidsf]

Yes...it's a more or less constant higher pitched sound...not loud..but noticeable...and only when the drive train is under a light but steady load. I'm fairly certain it's gear whine from the rear differential. Wish I could post an audio file here but that best describes it in words. I've seen a few other pathy owners complain of the same. If under warranty, the dealer appears to replace the differential.

After thinking about it more, my theory about why this sound appeared after replacing my trailings arms is that the new stiffer trailing arm bushings are simply conducting much more of the whining sound (which was there all along) to the frame...to the body..and to me up front. I'm not too concerned (yet) because it only shows up under certain driving conditions, but if I were shopping for a used vehicle and heard this, I'd wouldn't touch that vehicle. As suggested by Ozzie (thanks), I may back-off the bushing pre-load a bit and see if that makes a difference.

BTW - I replaced the trailing arms with Dorman 905802, 03 and 04. The original bushings were totally shot...especially the lowers.

[Towncivilian]

Huh, odd. I just assumed the sound emanated from the rear window vents. Although perhaps we're talking about two different sounds here. You can upload a sound sample to Mediafire or take a video and put it on YouTube for us to listen to.

[suzook]

Yes...it's a more or less constant higher pitched sound...not loud..but noticeable...and only when the drive train is under a light but steady load. I'm fairly certain it's gear whine from the rear differential. Wish I could post an audio file here but that best describes it in words. I've seen a few other pathy owners complain of the same. If under warranty, the dealer appears to replace the differential.

After thinking about it more, my theory about why this sound appeared after replacing my trailings arms is that the new stiffer trailing arm bushings are simply conducting much more of the whining sound (which was there all along) to the frame...to the body..and to me up front. I'm not too concerned (yet) because it only shows up under certain driving conditions, but if I were shopping for a used vehicle and heard this, I'd wouldn't touch that vehicle. As suggested by Ozzie (thanks), I may back-off the bushing pre-load a bit and see if that makes a difference.

BTW - I replaced the trailing arms with Dorman 905802, 03 and 04. The original bushings were totally shot...especially the lowers.

Not sure if your still around...but I am wondering how the arms are holding up. I'm on a budget, and was thinking of getting the doorman or moog bars, but have heard they don't last. Let me know...thanks

[davidsf]

Yes...am still around. The RTAB's are doing just fine. The whining sound went away after a few days. My guess is that either the rear end settled in after being jacked up and that put things back in aligment...either that or the new trailing arms slightly changed alignment to expose a high spot on the differential gear and that wore down pretty quickly after a few miles of driving. In any event, it's all fine now. Inexpensive long afternoon project using after market RTAB's with pre-installed bushings. Impact wrench strongly advised...and even with that you may end up having to saw some of the nuts off with a cut-off saw. So suggest you have replacement nuts on hand....hardened steel ones from a good hardware store or the dealer.

[suzook]

Yes...am still around. The RTAB's are doing just fine. The whining sound went away after a few days. My guess is that either the rear end settled in after being jacked up and that put things back in aligment...either that or the new trailing arms slightly changed alignment to expose a high spot on the differential gear and that wore down pretty quickly after a few miles of driving. In any event, it's all fine now. Inexpensive long afternoon project using after market RTAB's with pre-installed bushings. Impact wrench strongly advised...and even with that you may end up having to saw some of the nuts off with a cut-off saw. So suggest you have replacement nuts on hand....hardened steel ones from a good hardware store or the dealer.

Thanks for the quick reply. One more question. Did you do just the lowers? Or uppers also?

[davidsf]

Both. Not too difficult job. 4/10. The uppers were easier. One tip...to reinsert the bolts aligned though the frame through the bushing, I found it helpful (about about 1/2 hour of "learning") to lower the rear end from the jack point I was using so that the holes lined up. Good luck.

[Chuck Tribolet]

The trailing arm bolts are supposed to be tightened with suspension loaded, including a half tank of gas and the spare on board (in the cargo compartment over where the spare goes underneath is fine, and makes things easier). The easiest way to do this is to support the rear with a floor jack under the diff.

Chuck

[donald]

The trailing arm bolts are supposed to be tightened with suspension loaded, including a half tank of gas and the spare on board (in the cargo compartment over where the spare goes underneath is fine, and makes things easier). The easiest way to do this is to support the rear with a floor jack under the diff.

Chuck

How important is torquing with all those standards?
I just did all my trailing arms, and torqued with a lift jack holding the rear diff up. I know it's unsafe, but it was easier access to the nuts with my torque wrench with the rear wheels and spare tire out of the way. And I only had a quarter of a tank . Though I did have jack stands underneath as a "catch" if suddenly the kiddy jack slipped out.

I'm also getting a "whirring" sound. The rear axle is considerably stiffer now with polyurethane bushings installed. It would make sense the rear axle is now "tighter" as I noticed while replacing the arms, it was not a simple drop in. The UTAs definitely need some coercion to get back in line with the brackets. I hope after some miles I'll notice the "whirring" sound go away :S