Diagnosing vehicle vibrations? 2012 M37x

[anewstartinchrist]

I'm having some vibration through the car which I thought might be a wheel bearing but I am leaning towards the driveshaft flex disk(Guibo) which I need to inspect. Already had the tires rotated and rebalanced so I know that isn't it. In the past it would become pretty pronounced around 60 mph but goes away eventually but as of yesterday, 5/31/25, at higher speeds I can still feel it. I can see the passenger seat vibrating and can feel the vibration in the steering wheel and from the transmission tunnel. I have considered the torque converter or the engine & transmission mounts but I am not sure. I watched this video here: https://www.youtube.com/watch?v=4yCxhyTlysw. And I am having the exact same symptoms so I may start there. This is a common fail point on Infiniti's too and when they fail they cause horrible damage that is costly. Tbh I'm not sure where the flex disc is on my M37x or even if there is more than one since it's full-time 4wd(X). I haven't had much luck on finding videos on Youtube specifically for Infiniti's. Definitely not for an M37 or M37x. Where is the flex disc(s) on the M37x and is there more than one? I've looked on the diagrams on PartSouq.com and it appears to only be one that's on the propeller shaft that connects to the rear driveshaft. Any help & advice is appreciated.

[VStar650CL]

I always use a sirometer when looking for mystery vibrations. It's what diesel and small engine repairmen use to set the idle on engines which lack a tacho, but they gave us one in the Nissan NVH course because it's also wonderful for figuring out the source of drivetrain vibrations.
https://youtu.be/oot2kFIrZoc

You can put it on the steering wheel and adjust it while driving on the highway in top gear with the torque converter locked up. Noting the engine RPM along with the sirometer reading lets you calculate, using the ratios in the FSM, what part of the drivetrain is producing the vibration. For instance, if the engine RPM is 2000 at measurement, top gear on your M is 0.776:1, so the transmission output shaft is spinning at 2000 / 0.776 = 2577 RPM. So if you read 2500~2600 on the sirometer then you know the vibration is in the output side of the transmission, the transfer, or the driveshaft. The stock rear is 3.357, 2577 / 3.357 = 768, so if the sirometer reads 750~800 then you know the vibration is in the rear diff, rear axles, or road wheels. If you get a number which doesn't match anything, then you can be pretty sure it's mounts or something else only indirectly related to the drivetrain. You can't eliminate any one specific thing with it, but you can at least preclude a lot of things you shouldn't be looking at. Barking up the right tree is almost always helpful.

[Yoda's Master]

have you tried getting your wheels balanced?

[VStar650CL]

He said at the top that he did, and rotated them. If the vibration is south of the diffs, an RFV (Road Force Variation) test on the wheels is probably still in order. Balancing doesn't necessarily cure every wheel and tire issue.

[DoN_BLaZe34]

I always use a sirometer when looking for mystery vibrations. It's what diesel and small engine repairmen use to set the idle on engines which lack a tacho, but they gave us one in the Nissan NVH course because it's also wonderful for figuring out the source of drivetrain vibrations.
https://youtu.be/oot2kFIrZoc

You can put it on the steering wheel and adjust it while driving on the highway in top gear with the torque converter locked up. Noting the engine RPM along with the sirometer reading lets you calculate, using the ratios in the FSM, what part of the drivetrain is producing the vibration. For instance, if the engine RPM is 2000 at measurement, top gear on your M is 0.776:1, so the transmission output shaft is spinning at 2000 / 0.776 = 2577 RPM. So if you read 2500~2600 on the sirometer then you know the vibration is in the output side of the transmission, the transfer, or the driveshaft. The stock rear is 3.357, 2577 / 3.357 = 768, so if the sirometer reads 750~800 then you know the vibration is in the rear diff, rear axles, or road wheels. If you get a number which doesn't match anything, then you can be pretty sure it's mounts or something else only indirectly related to the drivetrain. You can't eliminate any one specific thing with it, but you can at least preclude a lot of things you shouldn't be looking at. Barking up the right tree is almost always helpful.

Not to highjack this thread but dealing with what feels like a similar problem. I've changed out all 4 wheel bearings, replaced both front axles to no avail. My issue only persists at highway speeds. Do you think this is something Infiniti could diagnose? I've been hesitant to call them because I can only produce the noise at high speeds and the dealership is an hour away.

[VStar650CL]

If it's a vibration (as opposed to just a noise), the dealer will have a balancer that can do RFV, but so will most good tire shops. That's where I'd suggest starting. If it's just a noise, the place to start is a lift and a stethoscope to see if it can be reproduced off the ground. If not, the only way you may find it is with chassis ears, and since that's very time consuming, expect to pay dearly if someone else does it for you.

[DoN_BLaZe34]

I should've better clarified...seems like a combo of a vibration/noise. Also I've already had my wheels balanced as well as switching wheels. The noise still persists. Feels like it coming from underneath the car. My naive guess was perhaps my driveshaft.

Your sentiment about trying to diagnose is my concern...feels like I'm chasing a ghost.

[VStar650CL]

RFV isn't a balance, it's an analysis of what the tires and wheels are doing with rolling load and vehicle weight applied. If your vibrations are coming from a belt deformity in a tread or a hidden stress crack in a rim, balance won't fix it but RFV will show it up. That's why it's the place to start.

[DoN_BLaZe34]

Apologies, I wasn't stating that a balance was an RFV test, was simply trying to provide additional information as to what I've tried thus far. I'll reach out to the dealership and go from there. As previously mentioned I have the same issue despite having already tried two different sets of wheels. I'd be surprised if I had issues with both sets but crazier things have happened.

[anewstartinchrist]

I always use a sirometer when looking for mystery vibrations. It's what diesel and small engine repairmen use to set the idle on engines which lack a tacho, but they gave us one in the Nissan NVH course because it's also wonderful for figuring out the source of drivetrain vibrations.
https://youtu.be/oot2kFIrZoc

You can put it on the steering wheel and adjust it while driving on the highway in top gear with the torque converter locked up. Noting the engine RPM along with the sirometer reading lets you calculate, using the ratios in the FSM, what part of the drivetrain is producing the vibration. For instance, if the engine RPM is 2000 at measurement, top gear on your M is 0.776:1, so the transmission output shaft is spinning at 2000 / 0.776 = 2577 RPM. So if you read 2500~2600 on the sirometer then you know the vibration is in the output side of the transmission, the transfer, or the driveshaft. The stock rear is 3.357, 2577 / 3.357 = 768, so if the sirometer reads 750~800 then you know the vibration is in the rear diff, rear axles, or road wheels. If you get a number which doesn't match anything, then you can be pretty sure it's mounts or something else only indirectly related to the drivetrain. You can't eliminate any one specific thing with it, but you can at least preclude a lot of things you shouldn't be looking at. Barking up the right tree is almost always helpful.

Not to highjack this thread but dealing with what feels like a similar problem. I've changed out all 4 wheel bearings, replaced both front axles to no avail. My issue only persists at highway speeds. Do you think this is something Infiniti could diagnose? I've been hesitant to call them because I can only produce the noise at high speeds and the dealership is an hour away.

Time to bring this one back. You definitely didn't hijack the thread. I'm at the point where I'm considering replacing the front and rear propeller shaft assemblies. So far I've replaced the tires and had those balanced. That seemed to have helped the vibrations at first but they're still present. I ended up replacing the front wheel bearings and outer tie rods on both sides(only the front). After the wheel balance and fixing the boot that was leaking after the wheel bearing replacement(driver-side cv axel boot was over extended causing the boot clamp to loosen and leak grease), the vibration is worse and more constant now . The vibrations I've felt so far are in the steering wheel(comes and goes) and from the center of the car. Have you finally found the issue with yours? I'm trying to replace my crossmember(batwing) brace now but I have a bolt that the head previously broke off of and will have to extract somehow. This wasn't from my doing but from one of the previous owners. When I bought the car in October of 2024 I didn't have the vibration issues. Only a while after I had the cheap tires installed when I bought it, brand name Arroyo. I have all-season Pirelli's on it now. Despite the cold, I will have to get the rear end off of the ground and get the car in Neutral to check for play in the shafts. With just the front off of the ground, neither shaft seemed to have any play. But for the rear one, I didn't necessarily try to move it back and forth, I just tried to turn it. Check out my newer threads to see my other issues and pictures of the parts in question. Once I get the brace on, I will get the car up to speed where the vibration is and place the car in Neutral. If the vibration doesn't go away, then the only thing I can think of that may be the issue is the torque converter.

[VStar650CL]

Getcha a sirometer and do some math. It will definitely tell you which tree to bark up, wheels/axles, driveshafts, transmission. Then you can concentrate on the right suspects.

[DoN_BLaZe34]

Saw your PM. Still chasing my issue as well. I mentioned previously that I had scheduled an appointment with my local dealership. They claim to have been able to hear the noise but "couldn't properly diagnose" it due to my car being modified. So that was a waste of a diagnostic fee. I'm back to square one. Haven't had the chance to find an independent mechanic to look at it. The only one I've gone to thinks it's the driveshaft but he's guessing and doesn't want to put the car on a rack to check it out while getting the car up to speed.

[anewstartinchrist]

Getcha a sirometer and do some math. It will definitely tell you which tree to bark up, wheels/axles, driveshafts, transmission. Then you can concentrate on the right suspects.

Hey man atp I'm considering it once I try placing the car in Neutral while driving to see if the vibration goes away at highway speeds. If I do, then I will post my results and will need your help interpreting the figures.

[VStar650CL]

No worries, happy to help. With the TC locked in top gear, all you need is the vibration frequency and engine RPM. The rest derives from those.

[anewstartinchrist]

Saw your PM. Still chasing my issue as well. I mentioned previously that I had scheduled an appointment with my local dealership. They claim to have been able to hear the noise but "couldn't properly diagnose" it due to my car being modified. So that was a waste of a diagnostic fee. I'm back to square one. Haven't had the chance to find an independent mechanic to look at it. The only one I've gone to thinks it's the driveshaft but he's guessing and doesn't want to put the car on a rack to check it out while getting the car up to speed.

Awe man I feel for you . After I test my car on the highway after shifting into neutral to see if the vibration goes away, I will know my next step. I have to finish my batwing install and repair first. Tbh I may try using what the other guy mentioned in this thread, a sirometer. I could not find one anywhere except on Amazon here:
https://a.co/d/3uMaRWE . About your car, how modified is it specifically? Too much so, that they couldn't diagnose the vibration? I surely would not have paid then. If they knew the car was modified before taking the job then they should have refused the job. Sounds like a money grab for them imo. This is why dealerships are dieing, they can't resist screwing over their customers. But I digress . The oem rear propeller shaft assembly is around $1k, give or take $100-200. And the oem front one is probably in the $700-800 range. It is what it is, and it depends on where you get them from.

[VStar650CL]

Tbh I may try using what the other guy mentioned in this thread, a sirometer. I could not find one anywhere except on Amazon here:
https://a.co/d/3uMaRWE .

You may have better luck searching "Treysit" (the only company which still makes sirometers) or "Briggs tachometer" (Briggs & Stratton still uses them as a factory service tool). This is the cheapest one I see new on eBay:
https://www.ebay.com/itm/336013727662

[DoN_BLaZe34]

Saw your PM. Still chasing my issue as well. I mentioned previously that I had scheduled an appointment with my local dealership. They claim to have been able to hear the noise but "couldn't properly diagnose" it due to my car being modified. So that was a waste of a diagnostic fee. I'm back to square one. Haven't had the chance to find an independent mechanic to look at it. The only one I've gone to thinks it's the driveshaft but he's guessing and doesn't want to put the car on a rack to check it out while getting the car up to speed.

Awe man I feel for you . After I test my car on the highway after shifting into neutral to see if the vibration goes away, I will know my next step. I have to finish my batwing install and repair first. Tbh I may try using what the other guy mentioned in this thread, a sirometer. I could not find one anywhere except on Amazon here:
https://a.co/d/3uMaRWE . About your car, how modified is it specifically? Too much so, that they couldn't diagnose the vibration? I surely would not have paid then. If they knew the car was modified before taking the job then they should have refused the job. Sounds like a money grab for them imo. This is why dealerships are dieing, they can't resist screwing over their customers. But I digress . The oem rear propeller shaft assembly is around $1k, give or take $100-200. And the oem front one is probably in the $700-800 range. It is what it is, and it depends on where you get them from.

It's lowered, with aftermarket wheels and a catback exhaust.
Yeah their reasoning was absolutely bs but I didn't feel like arguing.

Yeah that's around the prices I'm seeing as well. I'm happy to pay the money to repair if it was determined to actually be my issue. I can't justify it under the current circumstances with the mechanic is guessing. Good luck with your situation, I'll be sure to keep an eye on this thread to check in on your progress.

[anewstartinchrist]

I may be tracing this vibration down to an issue happening to the rear passenger-side. Recently had a grinding sound coming from there and noticed the outer brake pad grinding on the outer portion of the rotor. I had a vibration that felt and sounded like a warped rotor at highway speeds(70-90+mph) when braking from those speeds for a while but I initially attributed that to something happening in the front end. I even had a sound that sounded like a wheel bearing going bad when decelerating at those same highway speeds but it wasn't happening every time I pressed the brakes. I already replaced the front wheel bearings a while back, just not the rear ones. I inspected & took apart the front brakes and rotors today, then cleaned and regreased everything. Upon inspection though, everything looked fine except for the bottom guide pin boot on the passenger brake caliper bracket, and it didn't rebound at all. It had separated from the bolt so it had definitely lost grease. I replaced the boots and removed the old grease on everything on both sides and used new high-temp silicone based grease. Upon test driving the car I still heard the noise but I can tell it's coming from the rear. I don't know if I can just have the effected rotor turned to try and save it but I may try. I think I either have a frozen caliper and/or the guide pins are having issues. Maybe the pads simply wore down and I just didn't get a warning, or maybe they're wearing unevenly since this is only happening on the passenger-side? The car has been at a couple of shops and so when I had it inspected there was no mention of the brake pads being low, as a matter of fact, the last inspection showed that they were fine and had plenty of life left. The grinding is definitely physically evident on the outer lip of the rotor compared to the driver-side rear. I have the PowerStop Z23 rotor & brake kit on the rear and the front. I actually had the front propeller shaft replaced a few weeks ago before this happened and STILL had the vibration. I also have the ENTIRE rear propellar shaft in case I need to replace it(long story).The same shop that replaced the front one even rebalanced the tires but that only temporarily helped the problem and made the vibration a little better. I will update when I can.