I hate to keep posting questions here but my recently purchased QX4 keeps posing perplexing dilemmas for me as a first time owner. Love the QX4 (when it's running).

The lesson of the week for me is 4WD = "Wear Item. Replace at 200K"

Just found out I need a new rear axle. To quote my mechanic "In 20 years I've never seen a vehicle do what yours is doing." It started off with an odd vibration between 40 and 70 MPH. I researched this on the forum and found that the majority of the time the problem is u-joints. I had those inspected and they are fine. The shop put the QX4 up on the lift and let the wheels spin under power and the rear end starts to shake the entire vehicle. He said something about the entire diff being pushed out. I don't know what that means since I haven't seen it myself.

To make a long story short I am trying to locate a replacement LSD rear axle. The mechanic says that the locking rear axle (with the same ratio) supplied for the 3.5l equipped pathfinder of the same year (2002) is not a replacement for the QX4 because the parts interchange doesn't show it as such. However, the gist I seem to be getting from the posts I've read is that they are the same. I have the code HG43 stamped on the plate attached to the firewall which I presume to be the same as the HG43 supplied to the Pathfinder series. Is the mechanic correct or can I get a locking rear axle with the same ratio from a scrap yard and use that. Otherwise I'm going to have to drop the LSD rear end and go with an open diff rear end to get the QX4 back on the road. I'd like to keep the LSD option if I can.

Thanks!

Exact same as an R50, with a minor exception on older R50s that had difference in shock mounting.

And I call BS on the mechanic's assessment. The rear drivetrain has 3 moving parts that can cause any vibration (driveshaft, axle, wheels/tires), and he's making it sound like it's some century-old mystery. He could have eliminated two of them in 5 mins. Did he try the test with the wheels off? Did he put a dial-gauge on the driveshaft to check out-of-round condition? If the diff was bad, you'd know pretty quickly.

There's a very short list of parts that can cause a problem. And all are very easy to fix. In all likelihood, you may have a bent axle shaft...finding out is as easy as removing 4 nuts and disconnecting the brakes. To fix that, you can pull an axle shaft off any R50 or QX4 (regardless of gearing) and swap it over. If the driveshaft is damaged/out-of-balance, any driveline shop can balance it. If it has bad u-joints, you can buy them on Rock Auto for a few bucks each (I keep spares), but you said those are fine. If the diff is bad, you can swap the remove-able 3rd member and leave the entire axle on the truck. You can even buy an open HG43 diff and put your LSD carrier into it, but an HG43 with LSD will probably run the same price and require no additional work (though I'd disassemble the LSD and see how it's holding up). The HG43 (4.363 gears) even appeared on some Xterras and Frontiers (though there was another HG43 that was 4.375; you wouldn't want those).

Bottom line: tons of easy fixes.

If you really want to swap the entire axle (and pay labor for the few hours that will require), you can pull any HG43 axle from an R50 or QX4 00-04...you just need to see how the rear shocks mount...the older axles had a different mounting style.

If you need any reference pics, let me know. I have a full spare rear axle and 3 HG43 diffs in my garage. If you're near AZ, I can even help with the parts or work!

Also, don't forget about the trailing arms bushings. I'm (poorly) assuming your mechanic ruled those out, but in the test condition you described, you'd probably be able to grab the trailing arms and wiggle them if the bushings were bad. But if everything was just hanging there, the trailing arms are largely out-of-the-equation, but a small enough driveline vibration would probably be enough to overcome worn trailing arms.

Also, I'd be curious to know about 4wd that doesn't last 200K...but then again, you have the all-mode 4wd system, and it's got more moving parts than the part-time system found on R50s.

Hawairish wrote:...you can pull any HG43 axle from an R50 or QX4 00-04...

I had a feeling we'd hear from you Don't you mean 01-04 though? If 2000 is also an applicable donor, then it should be back to 97 or so, right?

Excellent info as always!

Hawairish wrote:Exact same as an R50, with a minor exception on older R50s that had difference in shock mounting.
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If you need any reference pics, let me know. I have a full spare rear axle and 3 HG43 diffs in my garage. If you're near AZ, I can even help with the parts or work!

Hawairish,

Thank you for that! I'm going to take the QX4 to another shop that is more familiar with 4x4 repairs. I bought the vehicle knowing I would have some issues to deal with due to age and mileage (236K). I normally wouldn't consider anything with that high miles but the vehicle was in near mint condition exterior and interior wise when I purchased it (other than parking lot scars from people who shouldn't drive). I suppose any used vehicle is a gamble and some more so than others. I am the fourth owner and the first two owners took very good care of the vehicle, the third not so much. The miles (though they are still miles) are mostly highway driving. The first owner purchased the car in 2002 and sold/traded it in 2004 with 110K miles. The transmission was replaced at 110k as well.

The previous owner replaced the rear sway bar links and both lower ball joints. The mechanic said the tie rod ends had also been replaced. As I understand it the PO rarely (if ever) took the vehicle out of 2wd mode and also spent the majority of the time on the highway between two cities in TN.

After purchasing the vehicle I replaced both front CV Axles, new struts,mounts/bearings, new shocks, and all four rear trailing arms. I thought the vibration might be due to something wonky in the very worn out suspension but after all the previously mentioned repairs the vibration is still there. The vibration is as some have described it "like driving on rumble strips" and shakes the entire vehicle.

If I were in AZ I would take you up on your offer unfortunately I think towing from NC would be a bit cost prohibitive!

Yeah, NC's a decent drive out...but if you're a baseball fan, it's the place to be right now (forget FL).

So let's recap those symptoms. "Rumble strips" is a really good description. It still currently does this between 40-70? Does it do it at low speeds or any other conditions? When it was on the lift, it was just idling in gear and it produced a visual vibration (i.e., you could see the axle dance a little dance)? Are there any noises?

I would also suggest you have someone drive beside you on a freeway while at speed/condition. That other driver should be watching the rear axle and tires for bouncing. A bad shock and a slightly off-balance tire would allow that tire to bounce rhythmically in the wheelwell, as if it were reacting to a washboard road...or rumble strip. (However, if you observed vibrations during the mechanic's test, then it's probably not the shock. But, if he didn't remove the tires, he didn't rule out an out-of-balance tire which could cause vibration at low speed especially if the shock was fully extended while on the lift...it'd allow even small vibrations to transfer to the vehicle.)

How are the bushings on the panhard bar? This is the 5th link in the rear suspension that controls lateral (left-right) movement of the axle. The bushings aren't generally subjected to the same harshness that trailing arms are, but fatigued bushings will cause the axle to walk sideways like a bad night in prison.

atraudes wrote:

Hawairish wrote:...you can pull any HG43 axle from an R50 or QX4 00-04...

I had a feeling we'd hear from you Don't you mean 01-04 though? If 2000 is also an applicable donor, then it should be back to 97 or so, right?

Excellent info as always!

Depends...I'm not exactly sure when Nissan changed the shock mounting styles, and if it was with any of the half-year models or face changes. It may have actually been earlier than 00. But that's also in regards to the full axle assembly (everything wheel-to-wheel)...which I don't think is a bridge he'll need to cross. All the axle's internals are identical, minus differences between the open and LSD carriers, though.

If he's just needing the HG43 3rd member, or axle shafts, then yes, he can pull from any year R50 or QX4, 97-04, noting that 03-04 R50s only had HG43.

I'll wait to hear more about the symptoms, but I'd be surprised if it was anything axle related anyway.

Ok. I finally heard back from the second shop. They say it is the ring an pinion gear. It is worn and has a lot of play in it. Metal shavings have damaged the other gears in the "chunk" . They could rebuild it but say it is an unknown what the damage may be in other components. They recommend a complete swap. $1800 from infiniti (not!) or cost plus $400 labor if I can find a compatible rear end replacement.

Do you think it would be reasonable to just replace the internals and is that a job that's doable for your above average DIY? It's been a while since I got my hands dirty but I'm game to give it a try if it's a reasonably doable job.

How did they determine the ring and/or gear is damaged? Did they just drain the fluid and peep into the fill hole? Was anything on the magnetic drain plug?

I guess I'm still a little skeptical...chunks in the diff would've likely created a bit of noise and chatter, and probably would have grenaded the diff if they were big enough by now.

Nonetheless, if that's really the case, a 3rd member from your local junkyard probably runs about $150, and you could swap it into the vehicle as-is if you really wanted to. Skip replacing the internals, just swap it whole. It's a very DIY swap...literally sockets and wrenches (and a dead-blow hammer or mallet). If it lacks the LSD, you can swap your carrier into the donor diff, but it requires setting up the gears a little (not nearly as much effort as a true R&P setup in this scenario). If you really want the LSD and don't want to deal with the setup, hold out for finding an LSD diff. Beyond that, just need a new diff gasket, gear oil, and brake fluid to call it a day.

I provided a basic pictorial of the process to another NPORA member a while back whose diff did grenade on him, plus this at TheNissanPath: http://www.thenissanpath.com/viewtopic. ... 197705b7cd. Just gotta pull the axle shafts out far enough to clear them from the carrier.

Hawairish wrote:How did they determine the ring and/or gear is damaged? Did they just drain the fluid and peep into the fill hole? Was anything on the magnetic drain plug?

I guess I'm still a little skeptical...chunks in the diff would've likely created a bit of noise and chatter, and probably would have grenaded the diff if they were big enough by now.

Nonetheless, if that's really the case, a 3rd member from your local junkyard probably runs about $150, and you could swap it into the vehicle as-is if you really wanted to. Skip replacing the internals, just swap it whole. It's a very DIY swap...literally sockets and wrenches (and a dead-blow hammer or mallet). If it lacks the LSD, you can swap your carrier into the donor diff, but it requires setting up the gears a little (not nearly as much effort as a true R&P setup in this scenario). If you really want the LSD and don't want to deal with the setup, hold out for finding an LSD diff. Beyond that, just need a new diff gasket, gear oil, and brake fluid to call it a day.

I provided a basic pictorial of the process to another NPORA member a while back whose diff did grenade on him, plus this at TheNissanPath: http://www.thenissanpath.com/viewtopic. ... 197705b7cd. Just gotta pull the axle shafts out far enough to clear them from the carrier.

Thanks again for all the info. It sounds like a fairly straight forward procedure. I've located a locking carrier from a 99 pathfinder with 110,000 miles on the donor vehicle. At $175 it's marginally cheaper than the $1800 the Infiniti dealer wants for the full rear axle assembly. :-). I think I'm going to give this swap a shot and see how it goes. The JY will have the part ready for me next week. I will update this thread with my results. I'm wondering if I ought to just go ahead and grab the axles from the donor while I'm at it just in case the current axles have any damage...

heelsrtops wrote:

Hawairish wrote:How did they determine the ring and/or gear is damaged? Did they just drain the fluid and peep into the fill hole? Was anything on the magnetic drain plug?

I guess I'm still a little skeptical...chunks in the diff would've likely created a bit of noise and chatter, and probably would have grenaded the diff if they were big enough by now.

Nonetheless, if that's really the case, a 3rd member from your local junkyard probably runs about $150, and you could swap it into the vehicle as-is if you really wanted to. Skip replacing the internals, just swap it whole. It's a very DIY swap...literally sockets and wrenches (and a dead-blow hammer or mallet). If it lacks the LSD, you can swap your carrier into the donor diff, but it requires setting up the gears a little (not nearly as much effort as a true R&P setup in this scenario). If you really want the LSD and don't want to deal with the setup, hold out for finding an LSD diff. Beyond that, just need a new diff gasket, gear oil, and brake fluid to call it a day.

I provided a basic pictorial of the process to another NPORA member a while back whose diff did grenade on him, plus this at TheNissanPath: http://www.thenissanpath.com/viewtopic. ... 197705b7cd. Just gotta pull the axle shafts out far enough to clear them from the carrier.

Thanks again for all the info. It sounds like a fairly straight forward procedure. I've located a locking carrier from a 99 pathfinder with 110,000 miles on the donor vehicle. At $175 it's marginally cheaper than the $1800 the Infiniti dealer wants for the full rear axle assembly. :-). I think I'm going to give this swap a shot and see how it goes. The JY will have the part ready for me next week. I will update this thread with my results. I'm wondering if I ought to just go ahead and grab the axles from the donor while I'm at it just in case the current axles have any damage...

Hi Hawairish,
I don't know how they determined the gear was bad. I'll ask when I go to pick up the QX4. I kind of had to prod them to spend more time on the axle so I can't imagine they did anything more than the basics you mentioned.

Any tips you have time to share on the swap process are greatly appreciated. I read through the post from TheNissanPath and that helped me get my head around the procedure.

Many Thanks!

heelsrtops wrote: I don't know how they determined the gear was bad. I'll ask when I go to pick up the QX4. I kind of had to prod them to spend more time on the axle so I can't imagine they did anything more than the basics you mentioned.

Yeah, I'd definitely prod them about how they reached that conclusion, especially without draining the fluid (which I would've expected that they charge you for if they did), or putting it on a lift and spin some tires by hand (and then demonstrating the test to you). It absolutely blows my mind that a mechanic can propose a $2000 solution, charge $100 for reaching that conclusion, and not do $5 worth (let alone $100) of work to prove it. They might be right at times, but it's like saying the truck rumbles because of the position of the moon when you happen to be driving and you should get it fixed immediately otherwise every puppy in the world will die. (All, of which, is true, btw.)

I've got some other responses regarding the diff swap and JY questions lined up for you, but first: if I were troubleshooting this, I'd actually be checking out the driveshaft, the transmission mount, and the motor mounts before even remotely considering the rear end. The driveshaft always rotates 4.363 times faster than your ring gear or tires do, and an off-balance driveshaft (it's no small piece of steel) will vibrate your entire driveline (t-case, transmission, axle)...and a bad transmission mount will promote it.

Although the amount of work to swap the diff is rather straightforward in my opinion, but the amount of work to test the driveshaft is trivial in comparison: 20 mins and a 14mm wrench. The transmission mount can be eye-balled for cracks, and even a crowbar can expose any failures. Doesn't hurt to also torque the bolts down while under there.

Money being an object, that's how I would start. $0 test, along wth rotating the tires. If a JY driveshaft is cheap enough (any 4wd AT 3.5L should fit), I'd even swap that in as a simple test. But otherwise you could take the driveshaft to any drivetrain shop and they can have it balance tested and fixed in minutes for a nominal charge.

Also, would you say that you feel the rumbles as you're accelerating, or just when you settle at a speed range? A diff issue would present itself at all speeds, and because it has a very low tolerance for error, these typically produce some noise (like a one-time clank or a prolonged whine/hum/screech/clicks) before catastrophic failure. Have you had any event where an object may have struck the driveshaft by chance?

Beyond that, I'll gladly provide any details you need for the diff swap if you decide to go that route. I can even mock up the process via video if you think it'll help. I'd hold off on the axles shafts. Under very extreme circumstances would you ever need to replace both...like if the spider gears grenaded and damaged the splines. Even then, needing to replace just one axle shaft is usually warranted by some known event (like a collision, getting seriously stuck while 4-wheeling, falling off cliff, etc.).

Hawairish wrote:How did they determine the ring and/or gear is damaged? Did they just drain the fluid and peep into the fill hole? Was anything on the magnetic drain plug?

I guess I'm still a little skeptical...chunks in the diff would've likely created a bit of noise and chatter, and probably would have grenaded the diff if they were big enough by now.

Nonetheless, if that's really the case, a 3rd member from your local junkyard probably runs about $150, and you could swap it into the vehicle as-is if you really wanted to. Skip replacing the internals, just swap it whole. It's a very DIY swap...literally sockets and wrenches (and a dead-blow hammer or mallet). If it lacks the LSD, you can swap your carrier into the donor diff, but it requires setting up the gears a little (not nearly as much effort as a true R&P setup in this scenario). If you really want the LSD and don't want to deal with the setup, hold out for finding an LSD diff. Beyond that, just need a new diff gasket, gear oil, and brake fluid to call it a day.

I provided a basic pictorial of the process to another NPORA member a while back whose diff did grenade on him, plus this at TheNissanPath: http://www.thenissanpath.com/viewtopic. ... 197705b7cd. Just gotta pull the axle shafts out far enough to clear them from the carrier.

Hello again,

I've had to do some traveling for work and I'm just now getting back to this. Monday I picked up a very good condition open Diff from a scrapyard for $189. Is there a way to convert that to an LSD using my internal components? If not what is the setup process you mentioned for the gears when switching to a non LSD?

I spoke with the last shop when I picked the qx4. The mechanic said they put it up on the rack and also drained the oil. He was certain that it was the differential and said my best bet was to just replace the Diff and leave the rest in place. This shop does a lot of work (standard repairs and custom upgrades) on 4wd vehicles and they have always been very honest and straight up with me so I feel confident they correctly diagnosed the issue. I'm still trying to locate an LSD diff as that would be the simplest repair.

If your LSD carrier and its internals are in good shape, you just need to swap the LSD carrier over to the new/donor diff. Put the donor's ring gear on the LSD carrier, then reinstall it.

To set up the gears you'll just need a dial indicator and a simple tool to torque the side adjusters. I made my tool with channel aluminum and rivets, but I think Rugged Rocks still sells one. I'll get some links and pics later.

Hawairish wrote:If your LSD carrier and its internals are in good shape, you just need to swap the LSD carrier over to the new/donor diff. Put the donor's ring gear on the LSD carrier, then reinstall it.

To set up the gears you'll just need a dial indicator and a simple tool to torque the side adjusters. I made my tool with channel aluminum and rivets, but I think Rugged Rocks still sells one. I'll get some links and pics later.

Thanks Hawairish,

I'm getting ready to work on this this weekend and I'm wondering if I can just swap in the open diff until I have some more time available to work on it. Would it be a straight swap of the carriers or would it require other changes? I'm still not clear on that point. I'm going to keep looking for an LSD carrier but I haven't been able to locate one with a reasonable price tag. The one I purchased was supposed to be locking but turned out to be open diff. The closest one I've been able to locate, they want $300 for the entire rear end and won't separate the diff. The donor vehicle has 205K miles on it and I a little Leary of spending all that given the mileage. The carrier I ended up purchasing has so little wear on it that I suspect it was a replacement on the donor vehicle before it was junked.

I would also mention that I have had all four wheels balanced and the rims checked. Everything is good there. I'm going to replace the front wheel bearings this weekend as well (well I have aspirations of doing so but I'll see how it goes.). After I get the truck up off the ground I may just have my wife video the rear end spinning without wheels just to convince myself that it really is the diff.

Thanks again for sharing your knowledge with a pathfinder (and forum) newby!

If the open diff is the same gearing and spline count, then yeah, you can just swap it in. You should absolutely confirm the spline count on the side gears before doing anything if you didn't pull the diff yourself, or see it pulled from the donor vehicle. If you count 33 splines and see "48:11" stamped on the edge of the ring gear (HG43 right?), you're good.

I'd recommend a new diff gasket, which you can get at Rock Auto for cheap. You should also consider new axle seals if you have the time.

Swapping later is up to you. Pulling the diff, and putting it back up there is a pain (and I basically just muscled it myself). Pulling the axles multiple times is bad for the seals (be mindful about resting the axles on them, they're at the end of the tube behind the brake drum plate). Then there's the cost of gear oil (unless you plan to re-use...guess that wouldn't be terrible...it just has to be LSD-safe) and some brake fluid since you'll need to disconnect the lines.

But as mentioned, re-using your LSD is pretty straightforward if you have the mechanical aptitude. It's not terribly complicated, but is a little time consuming. You'll need a breaker bar and/or impact gun, something to hold the carriers (like a vice), torque wrench, thread locker, and some patience to set backlash.

This is the other tool I was talking about: https://ruggedrocksoffroad.com/nissan-h ... 57742.html. Doesn't have to be this elaborate...I made my from some scraps.

Hawairish wrote:If the open diff is the same gearing and spline count, then yeah, you can just swap it in. You should absolutely confirm the spline count on the side gears before doing anything if you didn't pull the diff yourself, or see it pulled from the donor vehicle. If you count 33 splines and see "48:11" stamped on the edge of the ring gear (HG43 right?), you're good.

I'd recommend a new diff gasket, which you can get at Rock Auto for cheap. You should also consider new axle seals if you have the time.

Swapping later is up to you. Pulling the diff, and putting it back up there is a pain (and I basically just muscled it myself). Pulling the axles multiple times is bad for the seals (be mindful about resting the axles on them, they're at the end of the tube behind the brake drum plate). Then there's the cost of gear oil (unless you plan to re-use...guess that wouldn't be terrible...it just has to be LSD-safe) and some brake fluid since you'll need to disconnect the lines.
.......

Hawairish,

After getting rained out several times I finally had an opportunity today to start this project. Alas, turns out the salvage yard gave me the wrong carrier ratio (50:11). Anyway, being the curious type and getting to be much less trusting when it comes to mechanics, I decided to jack the truck up and see the problem for myself. I wasn't sure what I would see but I was expecting to see some sort of vibration/ shake at the carrier and hear something at all speeds. That isn't what I'm getting at all.

The ujoint and carrier seem to spin smoothly at all speeds and the rear end in total doesn't exhibit any sort of odd behavior that I can tell. There is a loud "growling" sound that starts at the same speed that I experience the shaking when I'm driving. The sound seems to emanate from inside the brake drums almost like bearing noises. I have the rear of the car completely free to move so it's also odd to me that I don't see the whole thing shake if the diff is actually bad. I took a video of the test and you can hear the sound from the wheels when the truck reaches speed. The link is here:

http://www.youtube.com/watch?v=Ck3d1yh6Wnw

Sorry,

Uploaded the wrong video and had to delete it. The correct link is here:
https://youtu.be/IAKeLmEW--A

I went ahead and dropped the carrier this afternoon. I can't see anything visually wrong with it. Just a "paste" of fine metal filings on the drain plug magnet. I never did see any chunks of metal and don't see any visible damage to the gears. When I disconnected the passenger side soeed sensor(think that's what it is) it was covered in oil and the passenger side axle came out way easier than I expected. Pretty sure the oil seal is bad on that side. Also noticed uneven wear on the rear brake pads so I'm going to need to do a brake job too. Yay.

Hey heelsrtops, sorry about the late reply.

So first, I bet setting up the truck like that and running it was puckering at times...nice camera action! I was puckered just watching! Doesn't like there was any signs whatsoever of the wobble that previous mechanic described, though.

By chance, when you pulled the diff, did you push the axles shafts back into the axle and try turning the wheel hubs (easiest with drums off)? That would be a good test to feel out each side's wheel bearings. You're feeling for any sort of drag, ticks, hesitation, and just anything that feels jerky. With axles pulled from the housing, you can also do some degree of visual inspection on the bearings. But you can also do some other tests to see how freely the axle shaft rotates in the bearings.

With diff out, it would also be worthwhile to go grab a dial indicator and check for backlash on the gears. Pretty simple to do. The FSM has all the instructions for how to measure and adjust it. I used a digital indicator and magnetic base from Harbor Freight for my setups.

Rock Auto also tends to have the oil seals on clearance. I apparently inventory some myself.

Thanks again Hawairish,

Puckering is right. Most un-nerving thing I've ever done on a vehicle. My wife wasn't to keen on being the test driver either. I most definitely wasn't about to go under the car.

Looks like there's going to be some delay in getting a replacement carrier so I'm using the time to check other possibilities as well. I *should* have taken your advice about testing the drive shaft earlier but my confidence in mechanics got in the way. I pulled it off this afternoon and checked the u joints first thing. Since both mechanics told me the u-joints were ok I was expecting them to move freely on both axes of rotation. Nope. The front u-joint moves stiffly but smoothly on one axis but jerks like it has indexed positioning on the second. The rear moves smoothly on one axis but very stiffly on the second. I took dropped it off at the lone driveline shop in the entire town this afternoon for new u-joints and balancing. I won't see it again for a week due to the backlog of work they have.

I finished the drum brakes today and I'm ordering the oil seals tonight. Might as well take advantage of the situation and take care of everything that needs maintenance.

I tested the bearings as you suggested and I didn't notice any jerks or catches as I spun the axles. How freely are they supposed to spin? Very freely (wheel of fortune style) or should they slow to a stop after 1 or2 rotations?

Bad u-joints can make things interesting...curious to hear what the driveline shop says when they get around to it.

As for the feel of the bearings, they likely won't free-spin too much with the grease in them, but with hub and possibly drum attached, you might get 1-2 rotations from inertia. Best bet is using a bare hand on the wheel hub to rotate slowly...kinda like how you see criminals cracking safes in movies, if that makes any sense. The rotating motion should just feel consistent and smooth as you apply steady and light pressure (basically the smallest amount of pressure to get it rotating). Short of having the bearings in hand and off the axle shafts though, that's the only way I can best explain it.

Hello again,

Sorry to be so long posting back on this. I FINALLY got all the bearings, etc. that I ordered. They were initially shipped to Texas from AZ and got caught up in the flooding. When they finally arrived here in NC they were shipped to the wrong address and then sent to SC to get re-shipped to my correct address. By the time I had everything in hand, the driveline shop was backed up again so add another week delay only to get rained out after that.

So... here's the update.

The gents at the driveline shop said the driveshaft was out of balance and both U-joints were bad. Lesson here is you can only really tell if the U-joints are bad if you drop the drive shaft and inspect them. I had two different mechanics tell me they were fine. So new U-joints have been installed and the drive shaft balanced.

In the video I posted you can hear the wheel bearings "growling" so I decided to go ahead and replace those since the truck was out of commission and the diff was already out. I ordered the bearings and had the driveline shop replace those as well.

Did a break job on the rear breaks (shoes were shot) and had the drums turned as well.

Since everyone here in western NC seems to think that a Nissan LSD is made out of 24K gold with gemstone embellishments and should therefor be priced accordingly, I decided to locate a used Open Diff and install it just to get the truck operational again. I located a reasonably priced one about 1.5 hours drive away and purchased it. Herein lies the second lesson of the day: Always check the part yourself BEFORE you leave the salvage yard. Got it all the way home and realized the ratio was wrong (4.636 instead of 4.363). Queue up 1 month wait while salvage yard locates an appropriate replacement and another 3 hours total drive time to complete the exchange .

I just decided after all the other repairs were done to just install the original LSD and take the car out for a run to see if the problem was resolved. Short answer: No. Rumble strip effect is still present as before although the other repairs have definitely diminished the effect at lower speeds. It's still very pronounced at speeds above 55 though.

I went Friday to pick up the replacement diff and was looking forward to completing the swap this weekend and hopefully having my QX4 back. Guess what?
Since I took the wife's van to get the diff I told her to just drive the qx4 the few miles from the house to drop the kids off at school. Everything should be fine I said just keep it under 45. My beloved calls me later in a panic because the QX4 died at a stop light and wont run unless she has the accelerator depressed. Lovely. She was able to limp the vehicle back home so I went ahead and picked up the replacement diff intending to check out the problem that evening.

I went ahead with diff swap realizing that whatever the other issue was I still had to get that wrapped up so I have the diff installed but can't test anything until I resolve the issue with the truck not wanting to idle or run unless the accelerator is depressed.

So the situation now is that everything in the rear end has been replaced except the wheels, tires, and axles. I had the wheels checked and the tires balanced and was told that everything was fine. I'll update this thread again when I get the new problem solved and can test the vehicle with the replacement diff.

As far as the new problem, whatever failed, failed suddenly and completely. After reading a lot of scary sounding threads regarding the IACV and the ECU I realize I may have a bigger problem on my hands than the vehicle refusing to idle. The issue is consistent and not intermittent so at least i don't have that to contend with. I'm pretty sure at this point that the TPS is dead. I get infinite resistance when I test the component and no change whatsoever when the throttle opens and closes. The IACV may or may not be dead but I'm going to go ahead and see about replacing it as well. From what I read, I would have to do that anyway if the ECU needs repair and if not it would be insurance against a future failure.

To be continued.......

Man, your just having bad luck. Check your oil, mine eats it. When it gets low enough. I know, the wife will call. Truck cant idle or go over 10mph. I just tell her put the quart in thats in the back. Starts up runs fine until I get home to properly top off. Crossing fingers yours may be just as simple?

Hawairish wrote:Bad u-joints can make things interesting...curious to hear what the driveline shop says when they get around to it.

Hi Hawairish,

I haven't disappeared (and unfortunately neither has the problem lol). I have brief opportunities to work on the truck so my efforts are somewhat intermittent. Anyway, after replacing the diff the IACV blew and apparently took out the ECU so I've been chasing that down lately. I'm beginning to suspect that the problem may actually be originating toward the front of the truck. I've replaced pretty much everything on the rear end except the axles and from the look of them it would take one heck of a blow to bend them in the slightest so I doubt they are the issue. I've read that the front driveshaft spins even if the 4WD is not engaged so I think I'll start there and check the u-joints and have it balanced. All of the repairs I've done so far have at least lessened the strength of the vibration so I suspect the wear in the components was also amplifying the effect.

Rebelord wrote:Man, your just having bad luck. Check your oil, mine eats it. When it gets low enough. I know, the wife will call. Truck cant idle or go over 10mph. I just tell her put the quart in thats in the back. Starts up runs fine until I get home to properly top off. Crossing fingers yours may be just as simple?

Thanks Rebelord. Unfortunately, I'm not so lucky. At this point I'm pretty sure the ECU is damaged. I'll pull that this weekend and see what I find. I did replace the IACV and the truck will at least idle (at 250rpm) on its own but unplugging the IACV makes 0 difference in the behavior so I doubt the valve is getting any input from the ECU.

Ok. Truck is back up and running now. The ECU had a fried chip. I ended up ordering a replacement part and repairing the ECU myself. The truck is back on the road now with the same shaking as before but at least it's running again.

Back to square one, part two. Bummer about the other repair.

Yes, the front driveshaft does spin even without 4wd engaged. Many folks tend to replace the fixed front hubs with manual hubs, hoping to free up some mileage from drivetrain load and to reduce parts wear. If you suspect the front driveshaft is also out of balance, you can remove it and try driving around without it. That would also be a good time to grease it up (there's a zerk fitting on the driveshaft) and to compress/extend it a little to work the grease in.

Do you know if the driveshaft shop also checked for runout on the rear? I suspect they did if everything came back nice and balanced, but didn't want to assume, especially since the runout limit is very small (0.6mm). If you have a Harbor Freight nearby, one of their dial indicators and magnetic base may come in handy.

Revisiting some older suggestions, how are the rubber consumable parts like suspension bushings and motor/transmission mounts doing? Trailing arm bushings are a common consumable part and can lead to various driving characteristics. But take a peak at the transmission mount, too. It's concealed a bit by the transmission crossmember, but you're looking for cracks in the rubber (the mount is basically two u-shaped channels with rubber between them). You can take a floor jack and gently put some upward pressure on the t-case (don't try to lift the truck by it obviously) to see if it exposes any cracks. If it does look bad, you may also want to check out the motor mounts as best as you can (usually done by some stationary engine revs to see if the engine lifts a bit on the driver's side). The thing about the mounts is that there are only 3 mounts total (2x motor, 1x trans), so if one fails (typically the LH motor), the other 2 take on a fair amount of new load.

Sucks to be working up the chain like this, but it you no longer think it's the rear axle, time to start checking all the other systems.

Ok. Here's the latest update. A couple of weeks ago I pulled one of the front tires so I could check the bearings I had installed earlier and decided to swap the front and rear wheels on that side (again) just to make clear to myself that the problem wasn't coming from there. I noticed that the vibration was still present but had changed somewhat so it was clear that the tires were either contributing to or causing the issue. There wasn't much life left in the tread and some were worn unevenly so I decided to go ahead and replace them. Ever hopeful I took the QX4 out on the interstate with the new tires and unfortunately the vibration was still there and seemed somewhat worse. At that point though I was pretty convinced that the problem was definitely coming from the front.

This weekend I decided to pull the front driveshaft and see if that might be the issue. I realized pretty quickly that the bolts were not going to give in to the tools that I have on hand so I had a local shop pull it for me this morning. Took them 10 minutes on the lift and done. Sadly though, the vibration is still there although definitely not as strong as when the driveshaft was in place. Also, the rear of the vehicle is smooth now and has no vibration whatsoever so the problem is definitely coming from the front.

Just to recap work done on the front of the vehicle so far:
New tires and wheels balanced.
New struts and strut mounts.
New CV axles.
New bearings and races on both sides.

I suppose the front differential could be the culprit but I would expect issues to be present at all speeds if that were the case. The motor mounts seem to be fine and the front of the drivetrain is now completely disconnected from the transmission,etc. I'm really at a loss as to where to go from here.