I've got humming and vibration and clunking and I'm hoping that it is not rear differential but only U joints. I've ordered the parts and watched some videos but was hoping people in the community could chime in and give their input or experiences on the process of replacing the U joints. Seems simple enough but I've learned the hard way that some issues will always come up and having other people's input always helps. Thank you in advance!

The driveshaft is a precision balanced component. Be sure to match mark the mounting ends to the transmission and differential so you can reinstall it in the same orientation it was removed. Inspect the driveshaft thoroughly to be sure there are no dents. Even the tiniest ding will throw off the balance. If there are any defects in the driveshaft, it's toast. Get a good repair manual with step be step instructions. YouTube videos may give you a false sense of confidence yet they can be helpful. However, they are no substitute for written procedural instructions which will also include proper tool requirements. U-joints are fairly easy enough to inspect and test for being worn out or not, without removing them. Don't fix what's not broken. The differential pinion at the rear end of the driveshaft is also fairly easy enough to examine to detect a worn out pinion bearing or worn out differential gears without removing anything. As mentioned in previous advice you were given, check these things first. If it all checks out good, replace that non-LSD gear oil you put in 8mo ago with the proper LSD gear oil. The additive you put in at the time was not a substitute for the additives in proper LSD gear oil. If the LSD clutch packs in your differential are worn out and/or the differential gears are worn out, replacing the u-joints will not help. Replacing them won't hurt anything either, except for your wallet.

mdmellott thank you. I took it to a driveline specialist who put it on a lift and inspected the shafts and said they were in good shape. He felt the rear diff and asked how long it had driven that morning, it was a few miles to his shop, he said the diff was cool in temp at touch which was a good thing. He then showed me two drivelines. One where the u-joints were bad (loose), and good (relatively firm). He followed by telling to have confidence and try taking the shafts off to determine if they were bad or not. Very nice guy. No charge for 20 minutes of his time.

I ordered Moog u-joints. Greaseable rear ones and non front ones. $50 total on Rockauto.

The differential pinion at the rear end of the driveshaft is also fairly easy enough to examine to detect a worn out pinion bearing or worn out differential gears without removing anything.

How would I inspect this?

Again, thank you!

Alibireason wrote: ↑

Wed Apr 14, 2021 4:01 pm

How would I inspect this?

Raise the rear of the vehicle and support it securely on jackstands. Block the front wheels to keep the vehicle from rolling off the stands. Engage the parking brake and place the transmission in Neutral. If the pinion bearing is worn out, the pinion seal is very likely to be leaking as well. However, that is only a clue since the opposite is not necessarily true. (i.e. The seal could be leaking while the bearing is just fine.) If the bearing is worn out you should be able to crawl under the vehicle and grasp the pinion flange with both hands and aggressively push up and pull down on the flange to feel for any lateral movement. It should be rock solid if the bearing is good. Backlash in the differential gears is normal but excessive backlash is not. Grasp the driveshaft and twist it back and forth. My rule of thumb is that 3/16" of rotation is normal and more than a 1/4" is an indication of too much backlash. Proper measurements of the gears for acceptable or excessive backlash cannot be made without dismantling the rear end. The humming and vibration and clunking noises you are getting from the rear end are your most significant indications of a possible worn out differential.

Thank you I will do this check next week when I have some days off. On my Pathfinder there is a sticker on the rear diff that says LSD oil only but the front diff has no such sticker. Does the front diff require LSD oil as well?

Nissan recommends the same LSD gear oil for the front and rear differentials.

UPDATE***
I replaced the front and rear differential gear oil with the appropriate LSD type. I took it in to get the alignment inspected and they told me my front right strut was leaking and the boots were bad which would have caused the uneven tire wear and also road humming noise. Quote was about $900 for KYB struts, upper strut mounts, and bellows boot kits. Is replacing the front struts on a 98 Pathy something a DIYer could tackle, or should I leave it to a pro? Would I be able to buy a strut that comes with a new coil spring or would I use the old one (I recall reading recently about the coils breaking in a forum)? I just looked on ROCKAUTO and found Gabriel struts with mounts and coil springs included for $130 each. Anyone know if these are good struts or not?


I then went to the driveline shop and talked U-joints again. The guy inspected the ujoints and said they seemed solid. He then felt the differentials and noted they were only slightly warm, which was a good sign. He then felt the transfer case and noted it was very hot and weeping fluid, helping to pinpoint where my problems are stemming. He also thought that could be a cause of the vibration and humming, and told me to try taking off the front driveshaft and go for a ride. If the noise and vibration went away it would be a big indicator of the problem stemming from the transfer case. He also said to contact a transmission shop to confirm if I would be able to do that without ruining my car. Anyone familiar with being able to drive without front driveshaft?
Does anyone have experience with similar issues? Is replacing or rebuilding a transfer case an expensive job to have done?
Thank you!

The transfer case being hot is odd unless you are in 4WD. Do you drive around normally with the 4WD shifter in the 2H or the 4H position? Have you checked the fluid level in the transfer case?

As far as I know it's only in 2H. I can shift down to 4H and the green light comes on indicating 4WD, and then shift back up and the light goes off.
Last summer I replaced the transfer case fluid. I haven't checked since then but I will tomorrow and post after.

Alibireason wrote: ↑

Mon May 03, 2021 12:43 pm

"... my front right strut was leaking and the boots were bad which would have caused the uneven tire wear and also road humming noise.

He then felt the transfer case and noted it was very hot and weeping fluid, helping to pinpoint where my problems are stemming. He also thought that could be a cause of the vibration and humming.

Two different shop mechanics (pros?), two different answers to cause of humming noise. Often times the only difference between a pro and a DIY'er is hands on experience. Someone's best guess can be helpful at times but not always. The "humming" noise could very well be from uneven tire ware due to a misalignment issue and possibly even the "vibration" and "clunking" you have noticed which could also be attributed to a strut that is shot. The hot transfer case may simply be heat transferred from the transmission but check the ATF level in the transfer case to be sure it hasn't leaked out since last summer when you had last changed it out.

As for the strut leaking, this is a DIY project if you have spring compressors. The KYB struts are fine replacements for the most part. I replaced mine with KYB Excel-G 3yrs ago and their performance is still excellent. However, the KYB strut mount bearings and bellows are lousy. I had to replace those KYB parts in less than a year. For those parts, I replaced them with OEM. The bearing itself is likely the only thing needed in the mount kit so replacing that with an OEM bearing is your best bet. The other original steel parts of the mounting hardware are fine to reuse unless they are rusted out. The OEM bellows have a unique bumper attachment to the steel seat at the top of the strut spring, which is not part of the mounting kit so you have to use the original. The KYB bellows do not attach well to this feature so the bellows end up falling away from it. OEM bellows and Febest NSHB-001 bellows are identical in form, fit, and function so it would be best to stick with what actually fits with your OEM strut parts. I have no experience with purchasing preassembled strut assemblies. I know they could save you time and you won't need a spring compressor but I can't vouch for the quality for any of those aftermarket solutions, like Gabriel or others. Although Gabriel does have a good reputation for quality, at least they did back in the day when I last purchased their product.

I'll let someone else chime in on driving around without the front propeller shaft. I have read on this forum, others that have done that. I new or rebuilt transfer case replacement is gonna be a big chunk of change.

I checked the fluid in the transfer case and it started pouring out as soon as I pulled the fill plug. It was still a good pink color. I also dropped the transmission pan and replaced the filter and fluid. I had replaced the fluid about ten thousand miles ago. The color was burnt and the magnet in the pan had a LOT of metal on it. The filter also had some chucky pieces that I could see after shaking it a bit to get them out of the corners and visible. I've included some pics. I have no idea the last time the filter was changed. Pathy has 235k miles. Is it just me or is that a LOT of metal on the magnet, and should the tranny fluid be that dark after only 10k miles, and the metal chunks, is that normal?

It's safe to say, I think you found the source of the humming, clunking, and vibrations. It's also safe to say, I think your transmission is living on borrowed time and has not much life left in it. None of what you show in your pictures is normal. Not even close to normal.