Alright.. So my 3.9 whines a bit..(350EVO)
I know that the backlash setting is what determines tight/loose, whine/no whine. Has anyone had this problem? Have you had it adjusted to stop the whine? I'm looking for some feedback. I'm considering taking it back in to be adjusted.
The sound in 6th gear around 60mph comes and goes with the throttle. It's annoying and I dont like explaining it to my passengers.
I have read alot of threads about the final drive, and a bunch of guy's have whine and say it's normal.
Who has this mod and it's totally quiet?
Thanks!

 

If it whines, the ring/pinion gear is too tight. Go back to the shop and have it re-adjusted.

 

explaining it to passengers is the least of you worries, take it back to get adjusted

 

I asked the installer and he said its within spec that 350EVO supplied.
Its loose, not tight. It only whines at certain rpms/speed. I believe if it was tight, it would whine all the time.

 

Something is wrong, it's not supposed to whine at all.

 

Bump.. I appreciate everyone's feedback thanks!

 

You could try different fluids? Or you could tell the guy, you want it tighter than what the spec calls for. Maybe call 350 evo and ask them?

 

Isnt it the other way around (whine = loose)? I had the 350evo FD on my old G35 and I had some whine as well.

 

Usually when it whines, it's too tight. Too loose it's "clunky" Not always the case though, there's always the possibility of variances in every setup.

The whining can also be caused by bad bearings.

 

Yes, too tight whines. The whinning is also accompanied by extra heat! This is where the damage comes from. You could get an IR temperature gun and test a friend's stock diff after 15 min driving verses yours. This will give you an indication if you have or WILL have a problem in the near future... Not sure what "safe" temp is but I'm sure someone here will chime in.

GL, I'd fix it if I were you though

 

O HAI
I have a 3.9 350EVO gears/Cusco diff/SPL solid mounts combo (bought whole pumpkin used from member), there is a bit of whine when throttle is applied, but it is very faint and unaudible when windows are open or stereo is on. I was attributing it to the solid mounts transmitting drivetrain noise into the cabin. I've been driving it like this for about over 2K miles and it didn't get any worse. Should I be worried?

 

whining is not normal - it can happen, because setting the rear up is time consuming though

it's a backlash issue, and yours is too tight. You can try to play with different fluids...it may get better, but the real solution is to have it torn apart, and put back together correcly shimmed

 

...

 

my reply was directed to the OP

 

It should make no noise at all. I also have the Central 20 3.90 gears and they made no noise at all. No whine or grinding. After 1500 miles I changed the gear oil, and no metal, so perfect gear teeth seat.

Make sure they replace, not reuse, all four bearings. This adds an extra $180 to the bill, but well worth it longevity wise.

 

I used all new parts when doing this mod. Bearings, seals, fasteners, crush sleeve, nismo cover, KAAZ lsd, flanges, SPL bushings.
I think I remember the dude at the shop saying the backlash was .11.. Anyone know the specs?

 

*UPDATE*
I had the diff re-shimmed and the whine improved a little but is still there.
It's not a consistent whine but just at 65-80mph when on/off throttle.
After LSD break in oil change there was trace metal on the plug. "Nothing to worry"
The second oil change there was no metal.
So I guess some gears are noisy? Would anyone agree that every gear set is different, and some produce noise?

 

They should not make anymore noise than the OEM pieces. The only other thing that can affect the noise level, assuming it's shimmed correctly, is the preload on the pinion bearings themselves, or worn bearings

You've also got solid diff bushings, and an aftermarket diff, which can contribute to more noise as well

 

Ya I agree Adam.. SPL describes the noise as being at 80mph and slight..
I can identify this noise.. I have been looking around a bit and I found that this was based on just the large bushing that is in the chassis. Apparently the other two that are mounted to the diff are the ones that allow more noise to be transferred to the car.
I am going to try the stock rubber ones (diff mounted) in the spring and see if that eliminates the whine I'm hearing.

 

cool - or just turn the radio up a bit