First off, I'd like to thank all of those who went before me and provided info on their 4.08 install. I couldn't have finished my install without your posts. I have a 2012 G37 Coupe Journey with a 7spd AT transmission, and I installed a 2009 G37 model 6MT differential with 4.08 gears that I put into it myself. So far so good...

I bought a 2008 6MT propeller shaft from a G35 so it would bolt up to the 6MT's differential's 4-bolt flange...except it didn't fit! The center bearing mounting bracket didn't line up with the mounting bolts on my car. Also, the propeller shaft on the 2012 7AT doesn't unbolt forward of the center bearing so I couldn't just use the back half like others in this forum were able to...and besides it was too long.

I solved this by buying a 1 piece carbon fiber propeller shaft from PST (61 and 9/16" long).



When the 1 piece carbon fiber propeller shaft arrived I was able to complete my build just this past weekend and my car drives beautifully. Much more pick-up and I'm very happy with the performance.

I'm in the break in period now driving my car to work (will change out the gear oil this weekend) but I'm getting the dreaded "Service Engine Soon" light on my dash.

I pulled the OBDII code and it's P0500: Vehicle Speed Sensor Error. I can clear the code, but it only comes back after I turn off the car and start it up again after driving a distance. When the Service Engine Soon light comes on, the car does behave a little off. The idle RPM's are about 200 or so higher (~1000rpm) vs. 750 or so, and it get's a little jumpy downshifting during deceleration. When I clear the error code, the car is back to normal.

Has anyone else had this problem with a 4.08 install? I'd appreciate any help or guidance on how to fix this problem. Help!

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Nice! So you've installed the 4.08 gears yourself or did it come that way with the 09' MT diff? I have the 4.08 myself sitting in the garage due to dreading labor costs. I've looked up at some write-ups but never found anyone who actually installed the 4.08 gears themselves. My only problem I believe I'll have is the shimming for the backlash. Wonder if you can give me some pointers on that etc.

Sorry to hear you're having SES problems hope someone can chime in and help you with that.

 

Huwee06: I put the gears in myself. It took a long time, and I had to buy a few tools to do it. Had I known just how much time and effort it would take me I probably would've tried harder to get a shop to do it for me! However, now that I've done it (and learned a lot), I'd definitely would set up gears again myself.

 

Did you get a tune? Im pretty sure you need them with the gears.

 

here is a post from a guy on the 370z page had the same problem 7AT 4.08 gear swap review - Nissan 370Z Forum

 

RPG11 Thanks for the link! I'll give Specialty Z a call and see if they can update a G37 ECU like they did for the 370Z.

As for a tune, do you mean a ECU tune such as Uprev? I hadn't planned on getting a tune since I put the gears in. What do you think it would effect?

 

Before the G i was into muscle cars and although is not the same car the principals are the same you need a tune to adjust your transmission to the new gears and it probably threw your speedo off and might be getting wrong MPH readings. You can flash the ECU but if I was you I would go Uprev or Ecutek.

 

There are issues with running the 4.08's with the 7spd. Its going to effect your adaptive cruse control, ABS, traction control, dynamic vehicle control...everything to do with the engineered tables that Infinti tested.

The ring and pinion in your car originally I believe... off the top of my head is 3.39:1
The speed table or engineered mathematical nightmare will allow a 5 to 7% difference in reading for most cases(which you've exceeded), due to tire wear and slightly different tire sizes that people will try to put on a vehicle.

So with all that in mind your option would be to look for a 3.69:1 ring and pinion gear set, take your diff out put in new ring and pinion, make sure its lashed and shimmed rite, install and your off to the races. Or live with an erratic....... just think of what's affected and how that may cause an issue when you don't want it too.

You can spend all kinds of money on a meathead trying tune it out. Im sure he'll have the ECU just dialed in like crazy, but whats the ECU again?? Will it tune how your traction control works, ABS and vehicle dynamics are affected....nope. Now things are not talking the same langue, it will talk with an accent if ya catch me. Or you can shut the entire system up and put a switch on your break light so it faults. Your car for now will run like a top with your dash board lit up like a Christmas tree and you can drift the ***** out of it with zero traction control. That way you don't have a separate nanny system talking (now) jibberish to your ECU. You'll also be minus a tail light.

Them are the best options I can think about, but don't listen to me because that wouldn't make sense..... Anyone can type on a forum, and it can cost you huge.
But thats my 2 cents.

 

That's another thing I actually want to try and DIY for the learning experience and don't mind a little down time do so. Did you use the shims off the OEM off original or new shims with a dial indicator to measure the backlash of the gear and pinion etc.

 

EddieJoe: I wrote the post you were probably referring to. I fitted the 4.08's to an 08 5AT.

I lost my cruise control, but that didn't matter much to me. It was a pleasure to drive.

I would not have recommended the 4.08's for the 7AT because of the original 3.39:1 ratio. Going all the way from there is extreme. However, you've done the work and deserve the final benefit.

Despite NBE-ON'D's disappointing advice, there are truths in there.

If you can't sort it out, you have a VERY marketable diff and shaft. But probably not for the 7AT.

Truth is, the 3.69:1 5AT diff with the 3-bolt flange would probably bolt up simple and they are giving them away on the net and ebay. No demand.

Good luck. Keep us posted.

JIm

 

SharpByCoop: yes, your posts helped me get this mod done! I think I've got a solution after reading RPG11's post. I had my uprev tune done by Church's here in SoCal and after talking with them they can update the ECU to keep the P0500 code from triggering. I'm off to see them tomorrow for the fix.

One thing that did occur to me was that the convertible G37's employ a 3.9 final drive gear, and that there must be a way to get some of that software into my car!

 

Huwee06: Yes, for setting up the gears I had to get new shims for the ring gear, but I was able to use the original pinion gear shim. If you're serious about setting up your gears on your own, read up on the article:

http://www.pirate4x4.com/tech/billavista/Gear_Setup/

I used all the tools and techniques documented. I had a few of the tools already, but I had to buy a few as well (dial indicator, in-lb torque wrench, and a shop press to name a few!) I probably spent $500 in tools! But hey, tools are forever.

The G37 differential is different due to the collapsible spacer on the pinion gear, and that took me 2 tries to get right. This was probably the trickiest part of the gear install. When you get to that point, I'll walk you through it the best I can!

 

Update: I went to Church's on this past Saturday and they plugged in their laptop and turned off code P0500. My Service Engine Soon light has been off ever since and the car is behaving properly. Idle RPM is where it should be at around 500-650rpm and it downshifts normally as well. So for those with 2011+ model year G's, you'll have to add this step to the 4.08 gear install to complete it.

 

Have to give props to SharpByCoop and ivoidwarranties (Jim and Kevin). Thought long and hard about doing this after swearing I wasn't going to do anything else to the G for a good while. Ok, a few months maybe. Followed their threads since both had 08 5ATs like me and suddenly the lightbulb burned bright. Damn -- had to do it! I bought Kevin's 6MT 4.08 VLSD and rear portion of the 6MT driveshaft. Bolted right in. The 3.69 diff is sitting in the garage having a pity party. Performance of the 4.08 gear ratio? Pure sex! It's like the G popped Viagra.....schwing! Again, thanks guys!

 

Dang, I'm happy for you. All my stuff is still camouflaged throughout the house. I need to set a hard install date so that I'm in time for a nice cool first time at the track. More on just how it felt.