There really aren’t a lot of threads in this forum that discuss swapping rear gears. I don’t want to discuss this from a 7AT vs. 6MT perspective, and I really can’t add to it from a mechanical point-of-view. But I did have the gears swapped on my 6MT Sedan, and I think it’s worthwhile to start another thread for discussion. At the very least, a place to put my thoughts down and maybe introduce this mod to people who aren’t aware of it, or haven’t given it enough consideration to be a worthwhile project.

As non-boosted power & performance mods go, this is no incremental mod. The bottom end has come alive with gobs of low-end torque.


COST

Ring and Pinion gears go for about $550.

A differential rebuild kit of bearings and seals goes for about $250.

Two quarts of gear oil… $35. (And then once again, about 1000 miles after the swap.)

Rear differential bushings… $100. (Not required, but if you’re there anyway, it’s a great mod.)

Professional Labor… 10 hours, give or take. However, at least 3 hours were burned up by the main diff bushing, so if all you do are the gears, an experienced mechanic can probably get you in and out in one day.


CONCERNS

This is something I started planning years ago. A variety of reasons kept me from pursuing it until this year, but I’m so glad it finally happened. All along, I had some anxiety that I was making my car un-driveable. Maybe a little too brutal. I was worried that these gears would make 1st and 2nd gear too squirrelly. That I would lose traction and get slapped back by traction control. I was worried that highway driving would drone me into the nuthouse with high-rev cruising speeds. People here got me worried about my speedometer being out of sync. Basically, I was just anxious about everything.

Turns out none of these concerns held water.

The car is not un-drivable at all. Granted, I have the RJM Clutch Pedal Assembly, and I think the drive-ability that component introduces makes up for a lot. I also have this amazing short-throw shifter from TWM. So all in all, shifting my car is a breeze.

First and Second gear are only squirrelly if I break lose, which is entirely up to me and my heavy foot. Plus, I have these really wide 275/35 Pilot Super Sports and a VLSD rear end. Basically, the car is as planted as I want it to be. But if I want to slide around a corner, that’s much easier to do now.

Highway driving is at a few hundred higher revs. There’s no getting around that. But the car is so damn loud anyway with this exhaust and intake and transmission mount, a little extra noise gets swallowed up. In about a day, it becomes the new normal.

And finally, about the speedometer… it’s fine. However the G measures speed, swapping in a new final drive gear-set doesn’t affect it. You can test this with any GPS speedometer app on your cell phone.


SURPRISES

These are some things I didn’t expect, bringing me to the crazy conclusion that the car is actually more drive-able with these gears than it was before.

On the highway, the new passing gear is 4th. Used to be if I wanted strong acceleration from a rolling 60 mph, I would dump it into 3rd and WOT, after which you find yourself needing to shift up to 4th pretty soon afterwards. Now, I can still do that, but I don’t have to. There’s so much more pull now in 4th gear, making 4th gear more broadly applicable to this kind of maneuver. It’s just better. You don’t have to make a jackazz of yourself with the lower gear.

Similarly, when attacking a low-speed turn, I would usually rev-match into 2nd gear on the approach, and power 2nd gear out of the turn. When you do that right, it can be a very rewarding experience. Thing is, it can also be brutal, because second gear can be brutal. And it’s easy to screw it up, no matter how skilled you might think you are at driving a manual transmission. Like the highway discussion, I can still use second gear for this maneuver, but I don’t have to anymore. There’s so much bottom end torque available in third gear, that I can use 3rd to power out of the turn.


RECOMMENDATION

If you drive a 6MT G37, and you’re considering dropping $1500 to $2000 on a set of wheels, but your automotive values prioritize the driving experience over how the car looks…

If you drive a stock 6MT G37, and you want a performance modification that runs under the radar, without adding an obnoxiously loud exhaust…

I highly recommend this mod.


SIX YEARS LATER

Re-reading this old thread, and I thought I'd add something. About a year and half ago, (September 2021), I participated in an Auto Cross event at this old abandoned air strip in the Southern Tier of New York. I'd done Auto-X a few times before, both with my G and previous cars, but only a few times. It's not really a hobby of mine, just something I talk my self into every few years. Anyway, on point for this thread and the gears, in Auto Cross with the G37 6MT (and most manual cars, I'm guessing), you never really leave 2nd Gear.

So think about that for a moment. Short rear gears moving power down low, and running WOT in 2nd gear around the track.

Pretty freaking amazing.

 

As always, great review & writeup John, so happy for you!
Post in the review section too when you can, thanks!

 

So what brand of gears did you get and where did you get them, or are these gears from another Nissan/Infiniti model? How did you decide on that gearing over another ratio?

One thing I am still not used to in my car is how high it can rev (I come from lots of turbo cars with low redlines). Even with all the mods I have already done, if I am in the wrong gear and decide to accelerate, it still seems like it takes a while to rev up to the power band and get up to speed. I would imagine different gearing in the rear end would change that pretty considerably. Do you notice it seems to rev faster or seem like your gears are shorter as a result of the change of rear end gearing?

 

These are OEM Nissan parts. I believe they came from the Nissan Frontier. I bought them from TheNismoShop.com, which is just an online front for the Parts Department at West Covina Nissan of West Covina, California. Paid $592 shipped. Z1Motorsports is probably a better source. I had an awkward experience with West Covina, so I'd recommend Z1.

https://www.z1motorsports.com/transm...36-p-4523.html




I was thinking the Vert's 3.916 gears wouldn't be enough of a bump over the 3.692 gears already in my diff. And I suspected the 4.36 gears would be undriveable. So I targeted the 4.083 final drive. Plus, everything I've read over the last few years pegs 4.083 as the sweet spot.


Yes, but it's getting normalized really quick. Funny how that happens. Yes, shift points are coming on you faster, but it's really just first gear that takes getting used to. You jump off the line and shift right away.

2nd through 6th are fine. Totally normal, just shifting at a slightly lower speed.

The torque is amazing.

 

So dumb question- you do feel like you are actually accelerating a lot quicker and not just shifting earlier?

Smart question- One of the brands we carry at my work is Nissan. This means I might be able to get a nice discount on the parts. When you have time, can you post up the part numbers? Seriously, no rush. This is not something I plan to do soon. Thanks!

 

It feels like whatever pull you normally have in the middle of any gear is now available down low. Particularly 2nd, 3rd and 4th.

So yeah... I'm accelerating a whole lot quicker. It's kind of shocking. Like I said, this is not an incremental bump.


Here's G37Sam's thread:

https://www.myg37.com/forums/drivetr...e-s-alive.html

 

Nice. Thanks! He brought up a good point about losing top end speed. On my local track (Road America) I think I would probably hit about 140mph at the end of 3 of the straights. (I am guessing as I have not driven it this year with the latest HP upgrades) I cannot imagine this would affect me as I have never even used 6th gear on this track yet, but I wonder how much top end I lose.

On a track you are usually trying to stay right toward the top of the powerband/rpm range. If you are noticing a large difference in acceleration mostly at lower and mid rpms, I wonder if this would be a good mod for my track days.

 

Mani with 4.083 final vs stock auto 3.357 final, 6th gear removed from calculations on auto. Both with 285 width tires and shift point of 7500RPMs




Looks like you will be a tad past 7000RPMs in 5th, presuming you are on 285s.

 

So with shorter gearing in the rear diff. I will be able to hit higher speeds in the first 3 gears, but lower speeds in the last 3 gears?? How is that possible? I run 275's out back if that makes much difference and also a M/T.

 

Theoretical max speed, at 7500RPMs with 275s and a 4.083 are

1st: 38
2nd: 63
3rd: 89
4th: 114
5th: 145
6th: 183

Not a whole bunch different from with 285s.

Not sure where you are seeing higher speeds in 1st-3rd then in 4th-6th. You want to be looking at the red lines on the graph with 1st being the lowest and each line above is the next gear.

 

Id tend to think if your goal is autox or drag that this would be of benefit..
but on a road course where you will live on 3rd.. 4th and 5th.. its a sacrifice..

 

If I accept that premise (and no reason not to, seems reasonable), it validates what I've been experiencing, which are huge gains in daily driving.

So much fun.

Hey 4DRZ... which gear do you live in the most on the track? I'm guessing 3rd. Wish I could show you what third gear is like now. But I hear you when you talk about proper road track behavior keeping the revs at the top of the power band. That makes a whole lot of sense.

 

For anyone reading this thread and wants to do a gear swap on an auto, 3.90 rear gear is what your looking for. Pretty similar to doing a 4.08 swap on a 6mt. It is the best mod you can do to these cars other than boost.

 

wow that's very very impressive, wish I could experience the difference.

 

Your numbers are skewed a little as you have the drive ratio on tranny 2 at 3.357 which is for the 7at, however we are discussing 6mt and should be 3.692.

John def have me thinking about this now. Im gonna have to make a special appearance up to the annual meet so I can take her for a spin

On serious note, if you havent already you may want to look at an oil cooler now. I know you dont drive your car all that often or far, but since you'll be running at higher RPM's in all gears and our cars run hot out the factory, something I would seriously look at.