Hi everyone - I think my first post here! I've been searching for a good thread/good answers for literal weeks now on this, but I just haven't found anything useful - a lot of people talking about wheel bearings or just saying get a new diff, no detail or explanations otherwise.

Had my 2008 G37S 6MT for coming up on 3 years next month - best car ever. Info for anyone to chime in - 2008 sport coupe, 6 speed, 90k miles, no accidents. Stock suspension. Rear end work - Z1 urethane diff bushings, high capacity diff cover, Z1 diff brace + RedLine 75w90 fluid 7k miles ago. New OEM transmission mount and driveshaft center bearing 1k miles ago. Have triple checked bushings install, diff ear bushings are installed correctly (fat ones on top) and the rear bushing is looking good. It is kind of touching the diff cover at the front? but at the back it looks perfect. As per the instructions, the original washers were all tossed.

Story: Rear end whine that is starting to drive me mad. I'm an auto tech so don't hold back on the details. It sounds exactly like gear whine - it is really loud between 2500-3100rpm, on light throttle only. Like 10% to 20% throttle and it just whirrrrrrrrrrrrrr. 50% throttle and it shuts up. Let off the throttle and it shuts up. Drive at 5k rpm and it's maybe there slightly, but basically non existent. It seems to be pretty quiet at lower speeds, loudest on highways due to light throttle to maintain speed right in cruising RPM range - I do know this drivetrain can be noisy. It does seem to be loudest in gears 4-5-6. Assuming has to do with the load applied. I also have a Zspeed stage 2 clutch kit with 19.5lb single mass flywheel. But this whine is out of the ordinary, and 100% from the rear differential. It also increases or decreases in volume with bumps, rear suspension loading/unloading which I find really odd specifically. I've been hung up on the pinion angle because of that? But there's no reason it should be off at this point. And yes the fluid is full and quite new! I just read something about the diff vent tube, I will have to recheck that soon. Diff bushing bolts have been retorqued after a week of driving

Thoughts: I may remove the diff brace to see if that helps. It may be transmitting more gear noise from the diff into the car via straight metal connection. The rear diff bushing contacting the diff cover is also something of note. But it is just urethane which I feel doesn't transmit sound this well. I could be totally wrong there? Very little experience with urethane bushings. I replaced the trans mount and center bearing in hopes it would help out, thought it did for a week, but it's back. Been thinking about rear subframe collars? Still not really sure exactly what they do lol. Also been thinking of the driveshaft u-joint, but it's not even replaceable! And I just spent $300 on a new OEM center bearing so that makes it more lame. The u-joint has a bit of a dead spot over center where it moves very freely before becoming nice and firm again - similar to the steering on some trucks/jeeps with a steering box. Otherwise no issue at all to be found.

Starting to wish I didn't take off my top speeds for an OEM muffler - if the car was stupid loud again maybe I wouldn't notice or care about some whining LOL. Sucks getting old I guess?

/story. Thanks for reading this far. Tried to be as detailed as possible! The whine sharply increasing in volume over bumps is probably what gets me the most. Just seems really odd. Could the rear subframe bushings be getting loose and moving, causing the pinion angle to change and cause the whine? Seems low mileage for that, but 6MT's are a lot harder on driveline bushings than autos due to the constant clutching in and out. Any and all answers appreciated! Always happy to learn something new. Added a pic of my bish to make up for the text vomit.

 

No text vomit found, that was a very well worded first post. Welcome to the forum, Slabba428.

With exception to this mystery whirr, it reads like you've got a fantastic car there. So if blame for this noise becomes increasingly focused on the rear diff, perhaps this is enough motivation for an upgrade to shorter gears, and a diff rebuild with new bearings. It's not an inexpensive mod, but it's so worth it.

 

hey, thanks! Haha about 90% of the help questions I try to answer on reddit are about 2 sentences

I think I'm gonna try Z1's subframe collars first. Looking them up now I am actually really impressed. And not even expensive. And my car has been penguin shimmying at times for a while. I love that these cars are 370Z's! It's so amazing for the upgrade department. I'm a former Nissan tech (split during covid, goodbye flat rate ) and working there is what made me buy this car. a Z that you actually love to sit in every day. I got it for an actual steal in 2019 right before the car market imploded too... I don't think I can ever sell it LOL. It is so spoiled.

Man 4.08 gears hey? That is crazy. I remember wanting to put 4.10s in my foxbody mustang. Which had a 5 speed from a pickup truck I feel. And even that was considered an aggressively short gearset. My gears are untouched (3.69 iirc? And people like the 3.92s from verts?) I already feel like first gear is a bummer. 4k rpm by like 10mph lol. How are 4.08s in a 6 speed nissan trans? Your first gear notch must be growing cobwebs

 

I had my rear gears swapped over five years ago now. What a fantastic modification to the G37 6MT. Here's a thread where I wrote about it:

https://www.myg37.com/forums/drivetr...6mt-sedan.html

I've no idea whether or not replacing the diff bearings will solve your problem. You're the Nissan Tech, and probably have far better instincts for trouble shooting these things than me. But as for going with a shorter final drive, it's a solid upgrade. Years later, and "new normal" and all that, it's still awesome.

With regards to the collars, every time I look into them I walk away thinking they're more appropriate for cars with high miles. And since I'm just over 50k, it's still a pass for me... but I never say never.

 

My past experience with urethane bushings on corvettes was not too good. I have no idea if that is a contributing factor, but I would check it out. There’s nothing wrong with stock bushing designed by engineers for everyday driving. If you track the car it might matter. Just imo.