Noise in Rear End After Lift/Trailing Arms - '99 Pathy

[SingleOwner]

Hi there folks!  First and foremost, thanks to everyone's inspiration and help here on the forum I recently lifted my 1999 Pathfinder SE (which I've owned since brand new in 1998).

 

SYMPTOM: I recently started hearing a rumble/howl from the back of the rig at highway speeds above ~55mph, but only while on the accelerator. Lifting off of the pedal but without changing speed (cresting over the top of a hill, for instance), the sound immediately stops and then comes right back again when power is re-applied.

TIMING: Lift was completed about 500 miles ago, but I really only first noticed this noise on the first highway trip AFTER installing all four new trailing arms 100 miles ago (torqued to spec with tires on ground).  The sound is pretty noticeable so I'm probably about 85% sure that this noise didn't start immediately after the lift, but rather started immediately after the trailing arms.

OTHER NOTES:
- In front it's lifted with OME HD coils, KYB struts and Fleurys 1" spacers.  In the rear it's got Land Rover 9449s and Bilstein 33185552s. 
- Manual hubs in front are unlocked and there is no accompanying vibration to speak of.
- After lifting but before the trailing arms were changed, the ball joints, control arms and front stabilizer bushings were all changed.  (Still need to change inner and out tie rods and rear stabilizer end links.)
- Rear axle in air (in Neutral), front tires chocked, there is only a small amount of play when rotating driveshaft.
- No thunking from the rear diff while driving (used to have this occasionally, but cured with a fluid change ~1,500 miles ago; proper LSD fluid used).
- There is a little play in the rear passenger wheel/tire when I push back and forth on the 12 and 6 o'clock positions. (Bearings?)
 
After a bunch of reading here, I'm thinking rear diff but why would new trailing arms introduce this? Could the lift have introduced this noise?  Could the noise just be the rear wheel bearing and the timing of when I first noticed it (right after the trailing arms) be a coincidence?

Your ideas and help are much appreciated!

Edited April 16, 2023 by SingleOwner
added detail

[Slartibartfast]

 

The symptoms sound like the rear end (worn bearings messing up the gear mesh), which makes sense given the rear end was giving you issues before. Could be the new control arm bushings are a little stiffer than the old ones and transfer the noise better.

 

The loose bearing is interesting/worrying. If I'm reading that right, the wheel is rocking up and down? Like a front wheel with a loose ball joint? I don't know how a solid axle would do that unless multiple things were pretty borked. The length of the axle shaft means it would take a lot of play at one end or the other. I assume you've ruled out loose lug nuts, spacers, junk on the mating surfaces? 

[SingleOwner]

Thanks, Startibartfast!  I finally had time today to get the rig back up in the air and double-check things.  Pulled the wheel off to look around and then re-attached -- No loose components (no spacers on this build) and no debris.  I have to think that maybe my paranoia maybe mis-identified a little bit of rotation of the tire as vertical play....   

 

After several trips at highway speeds I have used a laser thermometer to measure the temp of the rear diff just after parking:  Never read anything higher than 145-150* F.  (I'm just assuming here that abnormal operation in the diff would result in higher temps.)

 

I've wondered about tire balance, etc., but the fact that easing up on the throttle (without reducing speed much) stops the sound makes me think you're right -- Perhaps the sound has been there for a while but the now-stiffer trailing arm connection transfers the noise more (prior arms were shot, now on my 3rd set in its 240k mile life).

 

What's the average life span of a rear lsd differential in these anyway?  Had the automatic transmission rebuilt last year, so maybe the diff has a similar life expectancy???

[Slartibartfast]

The thunking before the oil change makes me think the previous change might've been done without the LSD additive. I've heard that makes the clutches chatter, which can lead to them breaking up. If clutch chunks escaped and got into the bearings, that could be your problem right there. 

 

Checking the temp isn't a bad idea, but I wouldn't expect to see much unless the rear end was absolutely shredding itself. You could drop the oil and see if any chunks come out with it. If you do end up diff shopping, look into the 3rd member from an early Xterra. Same 33-spline H233B, but they packed the LSD a little tighter than they did in the R50s. If you've gotta swap it out, might as well upgrade, right? If you want to really dig into it, Hawairish did a great writeup on repacking the LSD up to WD21 spec or better. 

 

Life expectancy for these should be pretty good. I haven't heard of many H233Bs outright failing, though the clutch-type LSD will wear out eventually. Mine's done over 250k miles and it's showing no signs of weakness, though I suspect it's had a pretty easy life.

[hawairish]

Noise is probably the rear u-joint due to the pinion angle post-lift.  I wouldn't expect it with only 9449s, though, but if new, they're probably still yielding a lot of lift.  I have the same symptoms on my truck, but with 9448s and 2" spacers.  The noise seems less pronounced these days, probably because the springs are settling.

[SingleOwner]

Thanks, @Slartibartfast!  For peace of mind, I may just pick up some more fluid and have a look at the current gear oil.  I changed it pretty recently so any chunky bits would be really noticeable.  Not too expensive and I might sleep better with the knowledge that the diff isn't ripping itself to pieces.

 

Thanks, @hawairish!   Good to know that others have had similar noises/symptoms post-lift.  The springs are definitely still settling, plus I only have ~100lbs extra weight in the back end (tools I usually carry around; no bumper, no spare carrier, etc.) so the settling process may take a little longer in my case than normal.  If it is the u-joint, is there any adjustment or anything that can/should be done that would help alleviate the noise? (I think I know the answer to that since I'm guessing you would have done that and wouldn't still have the same noise.)

 

Cheers!   

[Slartibartfast]

I hadn't thought about the pinion angle with the lift. That would make sense. Before dumping fluids, you could try loading up the back of the truck to compress the suspension a little, see if that calms the noise. If it does, then you know it's not the diff.

[hawairish]

Not really any off-the-shelf adjustment techniques, unfortunately.  You could check if the u-joint itself was worn enough that the change in angle is now exploiting it and maybe replace it, but I don't think it'll actually resolve the issue outright.  Only real solution would be new trailing arms that are either adjustable or longer.  On my truck, with all the lift, the pinion points upward a little more now, so to get it lower I'd either need shorter upper arms, or longer lower arms (realistically, shorter uppers would not be desirable, in my opinion).  For a non-double-cardan driveshaft like ours, you want the pinion angle to be parallel to the output shaft.  An angle finder would help confirm if the angles were in sync.

[SingleOwner]

Thanks, @hawairish!  This lift project has been quite a learning experience -- And it keeps going like the Energizer Bunny!  Next up, angle finder and pinion angles.  Might have to put it on pause for a bit while some other things are happening, but I'm looking forward to figuring this one out, too!

Edited April 26, 2023 by SingleOwner
correct formatting