What would it take to swap in the rear end from LSD G37S to base G37?
What sort of cost is involved? Is this something that can be done in a driveway?
I see there are two kinds listed, one for AT and one for manual. They have different gear ratios, should AT be matched with AT or is there an advantage from using MT?
Cpe & Sdn, rear, RWD, locking, AT (3.357 ratio)
Cpe & Sdn, rear, RWD, locking, MT (3.692 ratio), from 2/10
Cpe & Sdn, rear, RWD, locking, MT (3.692 ratio), thru 1/10

You can pick one up from a junk yard for $400-500, it seems like a pretty cheap upgrade.

 

I did this a few months ago. I meant to post up a quasi-DIY since I did remember to take some pics along the way, but haven't had the time lately.

To answer your questions.. It can be done in a driveway, but I used my friend's lift and it made the job MUCH easier in my opinion. The diff is heavy as heck so you will DEFINITELY want two people for the job. No extra parts are required, except perhaps, some gear oil - probably wanna change the fluid while you're at it. As for the process, you have to drop the exhaust, remove the sway bar, and some driveshaft shrouding. Then just disconnect the input and two output shafts, unbolt old diff, bolt up new diff, and reinstall the rest of the stuff.

Two more things on the diff itself.. The gear ratios don't really present any compatibility issues, they would just change the final drive ratio by a bit. However, the input flanges ARE DIFFERENT from AT to MT, so I'd recommend keeping it consistent if you don't feel like swapping those. Lastly, you will find that the drive axle flanges are threaded on your car (if its a non-S) AND also on the output flange of the S diff. This obviously presents a problem that is effectively solved by drilling out the threads on the S diff. This was straightforward, simple, and only added about 30 minutes to the job. Start to finish it took about 4 hrs and was a very worthwhile upgrade. It improved straight line traction by more than 50% and provides the ability to create on-demand, controlled oversteer when you're feeling enthusiastic. I'll try to post up some pics this weekend if I get some time.

 

That's great, thank you.
I am not very clear on the threaded output flanges. Are you saying that all three flanges on the LSD diff are threaded and the driveshaft and the axle flanges are threaded as well? Why would the LSD diff flanges be threaded, but the non-LSD one not?

Do the bolts thread into the shafts not the diff, or the other way around?

 

1) On the unit I purchased only the output flanges were threaded. The diff input flange connected to the transmission shaft with a nut and bolt.

2) Got me, but it was, so I dealt with it. Might not be that way with all of them, but it was with the one I got. FTR, the donor car was a 2011 G37S Coupe 7AT.

3) The bolts are inserted in between the diff housing and the output flange, slide through the flange, and thread into the drive axle. (BTW, you will need to loosen and tighten these bolts with a wrench because a socket will not fit in the small space between the flange and the diff housing.) Since my LSD flanges came threaded I had to drill them out. Wasn't really a big deal, although it would have been a lot easier if I realized that BEFORE I mounted it up. Woulda been much simpler to drill out the threads on the ground. Consider yourself lucky to have advance notice.

 

Again, thank you kindly for you response.
It seems like a cheap worthwhile upgrade to me.
The threaded part is strange, this would mean that on LSD rear end the drive axles are bolted in the opposite way from the non-LSD one

 

My pleasure. I'm glad to help out someone else considering this upgrade. You're right, it is a tremendous "bang for the buck" upgrade. It's amazing how much an LSD can change the dynamics of the car and enhance the driving experience. More folks with non-S models should seriously consider this upgrade. It doesn't require any special tools or skills, just some time.. and strength.

The threaded part IS weird. I came to the same conclusion that the LSD and non-LSD models connect diff to axle in opposite fashion. The 'why' is anyone's guess.. Fortunately, the threads on the diff flanges aren't thick or deep, so you can turn an S flange into a non-S flange with about 15 minutes and a drill bit.

Good luck, and let me know if there's anything else I can do to help!

 

If you wanted to go through the effort of adapting the drive shaft, the 6MT gear ratio would give you about 10% more torque available in each gear. Not sure you need it with the 7AT, though. First gear is already pretty low.

 

I agree on both points. Lowering the diff gear ratio is an effective and cheap way to increase torque multiplication and get power to the ground quicker. However, the main reason I switched to the LSD was the horrible lack of traction when accelerating from a stop. Part of this is because our engines make a good bit of power down low and the other part is the 7AT, like you stated, is already geared very low also. While a lower diff gear ratio may improve performance overall, the likely cost would be additional wheel spin "off the line" and a reduction in highway MPG. Neither were tradeoffs I was willing to make.

 

If anything, I'd get a rear end with a higher gear ratio for the sake of fuel economy. This motor makes enough torque for me and I am not interested in making it faster at this point.
The one wheel drive is really a bad choice, I had a first hand experience this morning when I went to change lanes in traffic and gave it a little to much juice.
It broke loose right away, and embarrassed me a little.

 

I think higher FD ratio should help with city mileage while lower help with highway mileage. Just curious how fast you were going that you spun at wheel? Summer tires should help with traction. Also I checked the part numbers and I think the axles are interchangeable through the base/journey/sport (non X) trim. I have no idea why they should change the bolting positions.

 

Yes, I stand to correct myself, I prefer lower gear ratio to help lower the RPMs on the highway. The tires are all season, I was just rolling in D and gave it a bit of gas to merge to adjacent lane. I did punch it off the line only once, and spun again, before the TC kicked in. The tires squealing make too much noise. I am to used to being able to just punch it and go, since my Saab just hooks up with the XWD system and G-Force summer tires.
The LSD and summer rubber should be able to fix that.

 

I just replaced my worn out OEM summer tires with Bridgestone Pole Position S-04. The traction is incredible now and what is most impressive is the wet traction. It is truly amazing what new rubber can do for your driving experience.

You might want to try a high performance set of summer tires before upgrading the LSD of the S.

 

Thread revival..

I did try that first. Bought a set of Michelin PSS. Did a little, but not enough for my traction issue, so the LSD became a must. These cars just put down too much power for a single 225-245mm tire to handle. Ya need to have at least 2WD.

 

this is a great upgrade especially with 3.69 gears in an auto. you won't notice the higher rpm's but you will notice how much more torque you are feeling. get better tires and you'll be able to use every bit of power your car can produce... if you don't want to upgrade, go the route of when replacing parts, replace with higher quality performance parts. you'll notice the difference...