4.08 Gear Install (7AT) Review
 

Hey Guys, when I was doing research on getting 4.08s for the 7AT 370Z I noticed there was a lot of people asking questions that were not getting answered. I'm going to give you guys some information I read up on and also my review after getting my gears installed yesterday.

Informational:

-The 7AT will lose cruise control. The light will just flash when you try turning it on.

-The RPM increase is around 600-700. See Videos of before and after posted below.

-Due to the RPM increase, there will be a decrease in highway MPG, but you can possible see an increase in MPG in city driving since it takes less work for the engine to get to the speed limit. Personally, I didn't notice a difference at all.

-For the 7AT you will need the differential from a manual 370Z to install the 4.08s.

-You can use the stock VLSD or an aftermarket one.

-The top speed will decrease from something like 200MPH to 180MPH. Realistically I doubt any of us will ever go that fast.

-Acceleration increases throughout all the gears and you will notice a loss in traction especially in 1st gear. Throw some good tires on there and you should be fine.

-Down Shift Rev Matching seems to be unaffected and seems to be working fine. I will drive it more in sport more within the next couple days and update if I notice anything different.

-The car is much more fun to drive now!!! :driving:

My Review:

I first want to start out by thanking Seb at SpecialtyZ for doing my install. He always does great work and answers all my questions. This is the only place I trust to take my Z. This time he did the gear install and GTM transmission cooler for me. Everything so far is working flawlessly!!!

After driving the car, you will instantly feel the difference. The car feels much faster and torquier. First gear is really short and 2nd and 3rd gear feel like your in a rocket. The fun factor is really where it's all at. The car accelerates so much faster throughout the entire RPM range, that its just a blast to smash the pedal and go.

Parts installed:
1. 4.08 gears
2. Gear install kit (Seals, bearings, shims, crush collar, etc)
3. Redline gear oil
4. Manual differential w/ stock VLSD

Seb swapped out the 3.69s from the manual diff and installed the 4.08s. Then swapped out my entire stock differential with the manual one.

Stock Gears 70MPH


Stock Gears 80MPH


4.08 Gears 70MPH


4.08 Gears 80MPH

That's a solid review, thanks for taking the time to so this!

Thanks the the review and the 7at trany fluid change thread!

Awesome.. I love my 4.08 gears, but I do get a little bit of whine at around 80mph. Cruise control works fine and the synchro rev match is noticeably affected unless down shifting while decelerating at the same time. I have 6MT

great review!

so what does that run you in cost including the diff? $2500 more or less....

yeah i am also interested in the cost of doing this to a auto

It all depends on how cheap you can find a manual 370Z differential. I got lucky and got one for a little under 400 bucks. As far as the rest of the stuff goes, here is the approximate amount they cost.

Gears (4.08s)= $535
Install kit = $300
Fluid = $30
370Z manual diff = best price you can find one for
Labor/install = $500, depends on your local shop.

So you are looking somewhere around 1400 +tax and whatever price you can find a used/new manual 370Z diff.

just want to be certain but it this that i need right, just the diff center

http://www.the370z.com/attachments/e..._2216-copy.jpg

No you need this from a manual 370Z

http://www.slidegood.com/media/catal...7565_1_355.jpg

i have a australian 370z 7AT do you think that matters?, i havent seen or read anyone thats done this in australia yet. and thanks for the info. I also fixed up my picture, uploaded the wrong one

is it possible to install the manual diff with the 3.69 gears on an auto? It would be cheaper and still increase acceleration. Not sure I want to go with 4.08. If it is possible I wonder if it would still disable the cruise control.

While you have the pumpkin off the car and opened up, may want to think about upgrading to a nice LSD. Kill two birds with one stone. So some of you may want to factor that into the price as well.

Not cheap, but really good mod. I had these gears and a Quaife diff installed on my 350z. Still debating whether or not to do it to my 370z.

i a have the 4.08s with the built GTM transmion.
when i had the stock 7 AT with the N/A mods on it the car car just runs increadably better than it does with the 3.3 gears.
It also shifts a lot faster in MM mode.
fuel mailage takes a big hit especail if you put your foot into.
Just wait till you do a 2000 rpm launch with the car and see what the difference is and if you shift at redline it really shifts fast,
i have the vid of the tack and spedo on the drag strip, i can email to a member if they want to edit and post it. Im not good a doing those things
thanks

Z

You drop the diff yourself you can save about $400

can i just get a manual differential and install that in a auto, without getting the 4.08 gears? is there anything else i would need? like a Stub Shaft assembly. sorry for the questions still learning.

As far as I know they should just bolt right up. I don't think any modifications or additional parts are needed if your just swapping the entire differentials. I do believe that the cruise control will no longer work still. People on the 350Z forums were switching to different size gears and also the manual diffs and they were losing their cruise control as well.

What exactly is the difference between the auto and manual carriers/diff? Just curious as to why you have to swap to the manual carrier/diff to do a gear swap.

I'll quote Jnaut on his explanation of this from his thread,

"the diff housing are the same between, the difference is inside , the carrier ( where the ring gear bolts up). you would need to change that carrier plus the stub shaft and axle if your going to run lsd or get a manual rear end out of a 350,g35,g37,370z."

I don't understand why the 7AT loses cruise control from doing gears. My biggest concern with that is UpRev uses the cruise control button to set the maps so will doing gears on a 7AT screw up UpRev?

up rev works perectly for changing maps with the 4.08s

Thanks for reporting on all of this.

Yeah I don't think the cruise control loss would affect UpRev switching. It's more about RPMs + wheel speed sensors not matching up the way the ECU expects that kills Cruise Control.

Q's:

1) Does VDC work now or is it forced-off? (which might actually be a good thing!). If it still works, does it seem to work correctly or does it make even worse corrections than usual?

2) The "manual rear end" thing... was your car a Sport Pkg 7AT with the VLSD before, or not? I'm just curious if this was about your rear end not being a factory VLSD, or if it was actually about the manual/auto thing, because the service manual doesn't seem to think there's much difference between manual/auto at the back, just VLSD -vs- Open.

3) You said 7AT revmatch "seems" to still work, but you needed to do some "sport mode" driving... that makes me a little leery yet since we don't know we're on the same page here. Can you drive the thing around in Manual mode and actually downshift, e.g. 4 -> 3 or 3 -> 2, and the rev match happens correctly for a smooth downshift (try it under braking, around 3.5K RPM in the higher gear before the shift).

If your car had the power, I'm sure this statement means that with the 4.08 gears you are rev limited to 180 vs 200 mph. That is the way I read it.

wWill let you know when put the stage 2 and stage 3 GTM Sc on it, i have the limiter set at 8200 rpm now all moter,

Z

180 isn't an unreasonable speed goal given a few mods and whatnot. I know for a fact the factory car can hit ~155-160. Somewhere right around there the ECU speed limit kicks in (which UpRev can eliminate). I kinda forgot about all that after I had UpRev on the car, since I really don't have any reason to try to go faster than that, but I wouldn't be shocked if the drag limit was a bit higher. Has anyone actually tested a bone stock 370's drag limit on flat ground without significant winds?

IMO around 180 and up is where aero dynamics play a hugh role.

Lets hit the salt flats baby.

Will the gears affect a 6MT cruise control as well?
This review sold me on the gears! Killer write up!

FYI.... We are just above 170mph at Daytona... Sooooooo unless you are tackling the salt flats there isn't /shouldnt be a problem.
Easy swap go to : www.car-part.com search and purchase a rear carrier / housing from a manual Z from salvage yard. When going that route...there will probably be less of a chance at needing to shim the diff unit itself when swapping gears...giving you a better line up on the gears and less gear noise.
Plus when selling the car etc... Makes putting It back a breeze.
Hard searching you can usually get them for $500 shipped. (entire complete rear carrier) you will have to use a little elbow grease when it arrives as the outside of the casing may be a little site to the eyes...but it's what's inside that counts. ;)
The viscous lsd's have one half shaft that is slightly longer that operates the viscous unit. When switching to a clutch type LSD... And I highly recommend OS Giken unit.... You will need to purchase a Left side half shaft from Nissan.( shorter of the two shafts)
Any guys seriously tracking the cars ...or not. I would seriously recommend sending the 4.08 gears to be micro polished.... It can cut down rear end temps by about 15-20 degrees... Doesn't sound like a lot....but it is with how hot these puppies run.

Personally I think 4.08 might push me off into 5th gear too often at the end of short straights in the 7AT, but I was considering upping to the manual's 3.692 ratio when I put in a clutch LSD, assuming it doesn't end up screwing up the 7AT's smooth downshifting. That's my main concern. You'd think it would just operate on RPMs, but the reports of 6MT's SRM getting screwed up makes me question that on the 7AT.

1. VDC still works perfectly fine. It does come on more than before because of course there is less traction now with the 4.08s.

2. My car was a sport package 7AT before and I swapped to a sport package manual differential. So basically I had the stock VLSD before and after the swap.

3. Yes you can drive around in manual mode and shift up or down. To me it feels perfectly fine and I do drive around using the paddles and shifter often. I have tried it under braking and it feels the same as how it was when stock. The one thing you will notice is that you will need to shift much quicker out of 1st and 2nd gear because of the gear swap.

No it does not screw up Uprev. You can still switch between your tunes like normal.

From my research it seems like the manuals cruise control still seems to work fine after the gear swap.

Nice review I had not found this before + Rep

The input shaft is different from the autos to the manuals on G37's. Is this the same for the 370Z's?

The autos use a three fingered flange while the manuals use a round flange with four bolt holes.

having a hard time finding a 370 6MT pumpkins. Will one from early 04 G35C 6 MT works? or one from 350Z?

The cruise control issue has to do with the logic. For automatics, the cruise control logic looks at both the transmission output speed and wheel speed. If they are inconsistent with one another the logic throws a code and the cruise control will not work. For the manuals, the cruise control logic does not look at the transmission output speed.

Top speed isn't 200 anyways, nor 180. 165 mph

Just to be clear on this guy.... I have a 7AT and just got a LSD out of a 6MT Sport. Do I still need to get a new pumpkin or can I use my stock one????

you can use your pumpkin as long as you swap everything all at once. I assume it is just a VLSD diff? if so and you did not have VLSD before, you will need new stub shafts.

It came with a (half shaft) is that what your talking about?

So I have a 7AT and did Differentials and Gears. I just got the car tuned by Visconti using EcuTek and he figured out how to get cruise control back!

When you drive the 7AT with the 4.08 gears. does the car bog a little during the gear changes after it changes gears ?
let me know , as i think that mine is closing the trottle bodies as it changes gears.
Its driving me nuts .

Z