Hi Guys,

Thinking about getting a 3.9 final drive installed.

Question is, do these create more of a 'whine' than stock?

Just curious.

 

Assuming the gears are of good quality, whine is the result of incorrect installation, not the ratio. Any competent installer should be able to get them to run as quietly as stock gears.

 

Whine is the result of gear mesh, not gear ratio.

 

It would probably be a good idea to read through section RFD of the service manual to get familiar with the procedure for selecting the shims to get the correct mesh during installation. It can be very time consuming and frustrating if you're not mechanically inclined and/or familiar with the procedure. It'll give you an idea of what the installer will have to know and what tools he'll need, too.

 

Can you elaborate on what gear mesh is exactly?

 

Thanks for the input guys!

The whine is only a slight one.

The reason i ask is because i may be potentially purchasing it from a fellow zed owner who has decided to upgrade their entire diff.

It will be a straight pumpkin swap, and i just wanted to know if it was normal or if its something more sinister.

 

This is what the hypoid gears in the pumpkin look like:



The larger one is the ring gear, and it turns the differential, which turns the axles. The smaller one is the pinion, and it connects to the driveshaft going to the transmission.

The "gear mesh" is the way the pinion and ring gears fit together as they turn. The pinion can be moved forward and rearward by installing shims behind the bearings. The ring gear can be moved from side to side with shims also.

The meshing is analyzed by coating the teeth with a special paint, turning the gears, and "reading" the pattern where the paint is wiped away by the contact between the gears. It takes some practice to read the pattern, decide which way the ring or pinion needs to be moved, and select the shim to move it the correct amount.

You also must have the correct backlash (clearance) between the gears, and the correct pre-load (static pressure) on the bearings. These settings may also be controlled by the shims, so the entire process can get very involved.

 

A slight whine is normal so I have learned. I have a 3.9 and noticed a whine definitely. I had my diff more accurately shimmed (cost me $500) and it improved slightly but not gone.
I had solid diff bushings installed at the same time and a lot of the noise is from the bushings in my case.
I have never had metal on my diff drain bolt.

 

the guys above are totally correct, whine comes from gears meshing too tightly.. another thing to think of is that while your back there, switch out the subframe bushing w a solid one as the rubber and liquid one is almost always shot. Theres no more isolation from the frame for the diff then but the overall clutch drop to actual acceleration is improved. ... and THAT my friend will give you gear whine at 80mph.

BUT it sounds great to me.

 

Whine actually tends to come from gears being installed "loose", not tight. Loose runs cooler (good for full race use). Noise is a 100% byproduct of the install. If you 1. reuse bearings 2. don't torque things exactly to spec 3. don't shim it exactly to spec, your propensity for noise increases dramatically. I currently have a full custom ring and pinion setup in my car that required alot of custom parts to work....and it's dead silent. It all is down to the amount of time spent by, and the skill level of, the person doing the job. It's time consuming, (alot of try, rinse, repeat, try again) to get it right.

you can't just switch the subframe bushing, you can only change the full set now. It is absolutely 1000% worth it, the change vs the stock rubber ones is amazing. I have them in my car, zero noise added

 

ha.. totally, thats what i get for posting too fast and not thinking.. loose is totaly what i meant.

I did the alum fr and rear bushngs and man, it sure added alot of noise to mine, but as you said, youve spent alot more time on yours then im sure i did.

plus one on it being a great addidtion.. after also doing whiteline LCA bushings and the new revised G35 compression rod bushings, it felt like I was driving a solid 100k porsche again. Amazing. And i dont have to pay 1100 a month for this car. ( i couldnt anymore if i wanted to anyways.. yikes) .

 

WOW!

Thankyou all for your replies! It is evident now that 'whine' is an attribute of incorrect installation.

winchman, thankyou kindly for you explanation and picture to explain. Totally clear on the subject now.

 

That's not true in all cases. Talk to BJ at 350evo.

 

Considering that every gearset for a Z is a factory Nissan part from somewhere it actually is true. The installation is everything (and I used to own 350evo 3.9s and ran them from their introduction through a few months ago, so am quite familiar with them)

 

I have a 2003 Nissan 350z Touring 6 speed with a Stock VLSD Diff.

The Car has 49,000 miles. I am the original owner.

It's about 450-500 WHP, and I do Drag Race it Some.

2500 miles ago I noticed a the Pinion begining to Whine on Decel and no load. And it has gotten noticablly louder, but I could live with it.

Now, I just installed solid Diff bushings and the Whine is a lot louder( 2-3 times louder), and Now I can't live with it anymore.

Any Ideas to correct the situation?

Is it possable to tighten up the preload?

Or do I need to rebiuld the Whole Pumpkin?

 

Try having it shimmed tighter but you might have to replace the ring and pinion.. Too bad I sold mine already.
How the heck do ya wear that out?

 

I have a whine as well with mine but it is faint. I had the tech reshim, replace bearings and reinstalled the gears (4.09fd) in the pumpkin twice but the noise still persisted. Seems like everyone that has a new FD with solid mounts are having a whining noise. As a hopeful remedy, I just bought the new whiteline poly diff mounts to see how much it'll quiet it down.

 

Not sure if this can help but I did a direct swap from an M/T pumpkin to my A/T and it caused a very slight whinning.

 

Not true, I did the gear setup myself and its dead silent with solid alum mounts.

I set backlash right in the middle of the oem tolerance zone. Same for side and pinion bearing preloads, mesh pattern right on the money, and a proper break in. I had low level whine for the first 100 miles but soon went away and now have zero noise.

So spend the time properly setting it up and you should have a quite final drive.

 

Fawk.