I just had a 4.083 final drive gear installed in my 07 base and as soon as I picked up the car I noticed a loud whine. It seems to start at around 40 mph and the pitch increases as the spead increases. I've searched the thread and there has been a lot of discussion saying it was normal from 79 to 86 but then it goes away. The whine that I'm hearing is consistent 40 mph and up and doesn't go away until I let off the gas. My fiance rode in the car with me and she says it almost sounds like I have a supercharger in the car. As soon as I give it a little gas it happens again. I had the transmission replaced by the dealership and the shop that I had the gears installed removed the diff and double checked everything. They swear its the throw out bearing but I'm thinking its gear whine from the installation. Anyone experience this type of whine with the 4.083 gears or is it quiet in the cabin? If this whine is normal than I can live with it, I just want to make sure. Can anyone chime in on this?

 

That usually means they assembled it with a little less backlash. Most likely its fine. I have the same whine with my 3.9 gears. HTH.

 

I have a little bit of whine with my 3.9 gears.

 

i had with my old mustang when i upgraded the final drive. i freakin hated it and drove me crazy.

 

My 4.08 conversion is as quiet as stock. Injected Perf did the gear swap for me...

 

As a GENERAL rule of thumb:
Whine = looser lash setting = diff gears runs cooler
No whine = tighter lash setting = diff gears runs warmer

Lash settings are determined by the shims (or combinations of shims) that are installed with the new gears & the experience/opinion of the installer. Mine asked which way I wanted the gear lash set with my 3.9 - looser or tighter. I went looser to run cooler...also added the Nismo finned diff. cooler.

 

If you run them too loose, the gear teeth will not engage properly. So you may be running a little cooler, but you're also wearing the face of the gears prematurely because they aren't fully engaging.

It's always best to go with factory specs & tolerences when adjusting lash and preload. The pumpkin should make no noise (whine, clicking, or thumping) on (accel, decel, or constanstant speed). If it does, the gears are not installed right. It's as simple as that.

 

My stock gears on my '04 had a slight whine at certain RPM's new....my 3.9 gears have same slight whine at certain RPM's.....been installed 4 years & 40k miles (multiple track days, autoX, tail of the dragon, etc) and no problems - no metal in fluid when changed twice a year, no visible wear after removing diff & cover (to inspect gears) when installing new HD axles.

No biggie - was just trying to alleviate the fears of others that have the slight gear whine...stock gears or otherwise....

 

Yeah, it's not black & white, but rather a gradiation. A little whine here & there probably isn't going to kill the gears. But too much or too little lash, and they'll eat themselves up in no time...

When in doubt, I like to stay within factory tolerances.

 

I figured it would have something to do with the gears, the whine wasn't present until it was installed.

 

So I just talked to the shop that put the gears in and they said the installation was solid. They offered to replace the Motul fluid they used with Nissan fluid to rule out that possibility.

 

could be worn bearing too

 

Confirmed with WestCo Nissan that the throw out bearing was replaced.

 

You can do what I've done for years...add a bottle of GM Diff. Additive to your diff fluid of choice (can pick it up at any GM dealership - small blue bottle - $9-10)....helps lubricate & quite down the gears. Have used it in my Z with each diff fluid change & previous cars as well - Corvette, RX-7, Mustang. As mentioned above, a small amount of whine is still there in my Z with the 3.9 gears, but it's not bad.

Also, have you had the tech that did the change ride in your Z to verify what you're hearing? If he's an experienced diff. tech, he'll be able to tell you whether it's ok or not after hearing it - IMO that's going to determine whether or not the install was "solid." Just like the level of the "cement mixer" sound of a lightweight flywheel is subjective from one person to the next, the whine you're hearing may sound normal to one person, but drive you crazy - ha! Just tryin' to help.......

 

I had a third-party transmission shop ride in the car and within 5 minutes of leaving the shop they said it was the diff. I'm going to see if this shop will work with me otherwise I hope this transmission shop will fix it, if its not already not damaged, and will have to go through the court. We'll see how it goes.

 

you need to remove the diff cover,put rear end checking grease on the ring gear teeth(about 10 will do).spin the rear by hand and view the contact pattern,there are charts to determine where you're at tooth contact wise and you need to adjust accordingly.if you installer doesn't know this go somewhere else.

 

This is what I did to check mine after the gear conversion.

Here's the page from the FSM for your reference: