Sometime in the next 4 to 6 weeks, I'll be having my mechanic swap out the original rear diff gear & pinion for 4.083 gears. I've been planning on this for a number of years now, and finally this is the mod I've scheduled for 2017. It's coming.

Anyway, he's asked that I find if there are any common tips or specific advice for the install. He's been a street/pro mechanic for 20 years, and I've been going to him for the last 10. I've a great deal of faith in this guy, he's honest and fair, and he has no qualms about doing this job. However, he's not done a rear gear swap on this particular car before, so it was a prudent ask, and could only help.

So... anyone?



As part of this work, he'll also be swapping in Whiteline rear diff bushings. That's a pretty straight-forward project for him, but if you've specific shop advice here, I'd welcome that too.

Thanks, gearheads!

 

There are a couple different ways the one bushing can be assembled that affects sound/vibration.




From this thread: https://www.myg37.com/forums/d-i-y-i...ushings-6.html


Whatever way mine was put on definitely increased sound/vibration, but I have a relatively quite exhaust, so it isn't bothersome.


IDK the "right" way for your setup, but be advised.


Good luck

 

Has your mechanic assembled differentials before?

There is a specific procedure to make sure the pinion is not too close or too far to the ring gear. https://www.ringpinion.com/Content/B...h-Patterns.pdf

Have you thought about buying a used diff and swap in the gears? Then you can easily go back to stock and sell the modded diff just incase you don't like shifting more often, noise, fuel economy or anything else.

Anyways, I look forward to your review.

 

Yes, he has, just not this car.

Thanks for the link... reading now.

Not buying a used diff for this project. Like many mods, it's a leap of faith based on research and planning.

NVH is already ever-present because of the exhaust, intake, and particularly because of the transmission mount. Not worried about that.

Mileage issues are a highway thing, and I only drive the car less than 5k miles per year, so not worried about that either.

Constant shifting is a joy... because of the short-throw shifter and the RJM pedal, so that's not a concern either.

 

Still enjoying my 4.08 gears and it's been 6 years since the install. Make sure you get new Bearing and seal kit..

 

Got that, too. Bought the rebuild kit from TheNismoShop last Fall. That, and two quarts of Redline 75W90 gear oil.

Say, is it best practice to flush & fill gear oil again after the swap? Do you know what the reccomendation is for this? That question has been floating around in my head for a while.

 

After 500 miles I drained the oil and put new in than followed manufacture recommend change

 

the install pretty straight forward to an experienced mechanic... had mine in for about 3 years.. 1st and 2nd gear is all the way enjoyable....

 

Stopped by to talk with my mechanic this morning, to get on his schedule for the gear swap. We're tentatively planning on next week. So... 10 days.

IIRC, these gears originated on the Nissan Frontier, right? My mechanic asked if the differential housing is the same on the Frontier as the one in my car. Anybody know the answer to that?

 

Diff bushings are installed. New gear & pinion are installed, along with all the bearings and bushings in the rebuild kit. All told, it was a 10 hour job, of which the main diff bushing chewed up many hours. Very messy job. The diff work went off without a hitch, although it's certainly a project needing skills, experience, proper shop & tools, and patience.

End result? Holy crap, my low end has come alive! There is so much torque rowing from 1st to 2nd to 3rd... it's kind of breathtaking. And yet, throughout it all, the car is totally driveable. In fact, there's a good argument to be made why the car is actually more driveable than before.

Amazing mod. So freaking happy. Here's the thread:

https://www.myg37.com/forums/g37-sed...6mt-sedan.html

 

I know they are very similar. The standard frontier rearend (C200) is likely just a solid version of the IRS diff (R200) in our cars. I'm almost certain I've read that the ring gears freely swap between them.