SharpByCoop

[EDIT] Thread Synopsis

1. To convert a 2008 5AT to 4.08:1 gears, you need to purchase a complete manual trans VLSD from a G35/G37/350Z/370Z
2. Purchase the Nissan Frontier gearset and related install parts to convert that existing 3.55:1 diff over to 4.08's (I used RDZ Motorsports for the complete purchase and installation in the housing)
3. The new gearset does NOT have the OEM pinion shaft extension which fits into the OEM driveshaft and rubber coupling.
4. This will work on lesser HP vehicles, but MY 600whp twin-turbo vehicle stressed it to the point of vibration.
5. To alleviate this problem, purchase a driveshaft from a manual trans 2007-up G35 or ANY G37 to 2012. (Earlier G35's won't work. Different sectional length and mounts.)
6. With the rear section of the MT driveshaft installed onto the related MT differential mounting flange, it will fit perfectly and has zero stress vibration and no added noise or disappointments.
7. Read the thread. There is more important info for other models.

[/EDIT]

Starting this separate thread because this deserves more input.

Just finished a lengthy conversion from the OEM 3.69:1 VLSD 5AT auto diff on my car, to a manual VLSD 4.08:1 diff. I used this informative thread as my guide (Thank you!)

I'm one part elated and one part deflated. Brought the car in and Jimmy's guys at The Shop installed the converted diff in one afternoon. He delivered it to me tonight. Nicely done.

They dropped it off with the old diff at my house.

Now, the 2008 diff has a pinion shaft which locates it into the center of the rubber mounted flange. I didn't know this until now.





This NEW one has no shaft to locate it:



I do not know of a set of replacement 4.08's WITH this shaft. So, unless you have seen otherwise, that's not available. Modification? Well, maybe....

Jimmy said: "There's a vibration going on when you accelerate. I don't know if it was there before, but it's there now." Huh? It was smooth as silk before.

So I took a test ride. The gearing is EXACTLY right and feels great. Nice jump from 3.69 to 4.08. I LOVE it. (It WILL blow the tires off in 1-2 but we knew that. It needs TLC unless I'm at the track with drag radials. I accept this.)

However….

When you step into it it vibrates real noticeably, then eases. I'm convinced this OEM shaft disallows distortion in the rubber mounts and keeps it centered.

I did some searching and found a thread with comparisons of the two style pinions:

DIY 03 G35 Coupe 5AT to 07 G35S 5AT differential swap - G35Driver

There are images on pg 1 and pg 2 of the distinctions. I'm especially concerned with pg two's reference to the rubber flanges showing and needing the support shaft.

It does not feel confident. It feels like it wants to break. Remember, I have substantial HP and torque over N/A.

So we may need to figure out Plan B? Has anyone here encountered this?

This begs the question: Why does the auto need the soft flange? Shall I consider a swap to a manual driveshaft and flange?

This is where I'm at. I am going to drive up to visit Rich at RDZ (who installed this gearset) to have him help evaluate Plan B.

Jim

TVPostSound

iTrader: (9)

I had my shaft out 2 weeks ago to do the diff bushings.

The pin at the diff actually lines up directly into the driveshaft.
The rubber coupler is not used for angular compensation, but only to absorb shock.
That being said, that pin is essential to keep the driveshaft aligned to the pinion flange.

So, now the coupler is acting like a u-joint, not good.

I believe you are correct, thats what is causing your vibration.

TVPostSound

iTrader: (9)

One more thing to add, the center support on the driveshaft had to be removed to pull the shaft from the diff, you should also check that its secure.

TVPostSound

iTrader: (9)

The shop should be able to install your original flange without dropping the differential.

TVPostSound

iTrader: (9)

Lastly, they had the diff out, why not change out the mounting bushings??
I did a write up about the G35 Whitelines working on a G37.

SharpByCoop

^^^ What is the benefit for other bushings? I don't do ANY road course or parking lot trials. Truth is, I never considered this.

So, I took it on a long drive today to visit Rich at RDZ, and flogged it a bit--just to see. Not quite as bad as I'd thought. What's adding to my alarms and vibrations is also a LOT of tire slip. I have bogus OEM rims and Potenza's as my winter tires (<< See avatar) which will be changed back within the week), and they light up in second, even third gear. Some of my perception is the tires not gripping consistent.

We stuck it up on the lift to observe, and everything was in order. I did not know this, but the two-piece auto driveshaft has NO universal joints at the diff. It's all through the rubber coupling. Ugghhh.

Infiniti supplies the auto experience to be sofffftttt.

So, the best answer might be a combination of things: lose the auto driveshaft, and go with a one-piece carbon driveshaft with true universal joints.

Problem is, having JUST installed the gears with the crush sleeve, the auto flange cannot simply be taken off and then the manual flange put on. The inner pinion crush sleeve is a one-time application. (Well, you could replace it and cross your fingers and remove the cover to check lash.)

Also: Does the nose on the manual trans driveshaft fit the auto output shaft? So many questions...

Right now, I'm going to wait for better tires and probably stick with it. I'm cautious, but a bit more confident after todays ride and inspection.

Does anyone know if the 370Z auto has the rubber coupling instead of universal joints?

Coop

SharpByCoop

Oh, discussing all the mechanical details, I've left out my road experience:

BOY do I love how this feels! It winds up quickly through each gear, and the shifts happen quicker and with less thrust. I was exactly at 3300 RPM at indicated 80 MPH, and now I'm at 3800. An increase of 500 rpm. Not crazy, but it hums more up there.

Overall I am really enjoying the change, even (especially?) on the street. My impetus is the performance gain at the track. That will come soon enough.

Atco has opened back up, and Jimmy want to put his street GTR in the eights. Mikey (our tuner) also wants in. We'll see.

Coop

Black Betty

iTrader: (60)

Coop with all that powah you are putting down and the 4.08 gear in back, do you not have any issue with traction during street driving? If you are slightly overzealous with the long pedal on the right does it penalize you by burning away some of your expensive rear rubber accidentally? Does it require better attention and pedal modulation to keep from breaking rear traction during moderate acceleration?

TVPostSound

iTrader: (9)

Because, you will blow the rear diff bushing, eventually!! Mine blew at 21K!! Z guys blow them even faster!!


There is an old trick!! I've done a few hundred diffs in my past.
Remove the pinion flange, leave the crush sleeve in, replace the flange, and use a needle torque wrench to tell you when you've hit the sleeve!! Had to go that route on old 80s Corvettes when the pinion seal leaked.


I think the 370Z AT also uses a coupler, but their shaft is 1 piece.

GTM makes the AT shaft, by using a u-joint at the back, and yoke it to a solid metal flange.
I finally got a straight response from them.

SharpByCoop

BB: Yes, yes, and YES. Stop making sense.

TVPostSound: Thanks for this info. Sounds like bushings and a single shaft with u-joints will be in my future.

Coop

Ivoidwarranties

iTrader: (7)

Coop, we need to talk. I'm probably going to delay a bit on 4.08s until I see if you figure everything out.

Ivoidwarranties

iTrader: (7)

From GTM's website:

$600 for an aluminum one piece drive shaft. They have a selection for 5 speed automatic and Coupe. If they make it (or can make it) so it connects up to your flange correctly, you would be set.

GTM is proud to introduce our own Aluminum One Piece Drive Shaft for the
Infiniti G cars. The stock two piece driveshaft weighs 46lbs while our
drive shaft weighs only 17lbs. This reduction in rotational mass
improves the acceleration and responsiveness of the car.

TVPostSound

iTrader: (9)

They do make one, but at 600 RWHP, I would be hesitant about buying one!!

Ivoidwarranties

iTrader: (7)

Which should support more power, stock two piece, aluminim, or carbon fiber?

Maybe Coop should look into seeing if there is a local place that can make custom driveshafts.

Maybe the driveshaft could be uncoupled and rotated an ear (1/3) and recouple (care to be centered) and see if the vibration is any different.

There are a few other autos with this swap, did they report any vibration?

SharpByCoop

IVW: OEM D/S IS supporting lots of power. At a weight expense, but no breakage. That is, until you leave out a centering pin?

I thought about losing the rubber and locking them together, but then there is NO universal action. Not even going to try.

That's just it: no one has reported anything odd about losing the centering spine. And there must be tens of later 350Z's and 370Z's who have done this.

(I say later, because up until 2007 the 350Z auto HAD a universal joint drive link. Nissan switched later in the years.)

I'm calling Sam @ GTM. He's already talked to me when I inquired about the alum shaft, and he recommended having a C/F one made instead.

I'll need a special one? Not sure, but it's going to be a M/T flange at the rear and an 5AT spline for the nose.

Thanks for the input.

Coop