1992 M30 Differential In 1987 Vg30 S12

Hey guys,

I'll need to spend some time writing this up. I'm now running an M30 differential in my 200SX. My nissan bud & I swapped it in with the new driveshaft from oem-surplus on Saturday. It was much more involved than we thought. I was of course hoping for a simple in-n-out but it didn't quite work out that way, but he's a trooper & stuck with me.

The M30 differential case is almost identical, just 1/2 longer for the sensor at the front. We ended up swapping just the differential and bearings into the existing differental case. I understand the 200SX ratio is a 3.9 and the M30 is advertised as 3.917 so we also had to swap my ring gear onto the M30 differential. I'll include this detail in the actual writeup but apparently SHIMS STAY WITH THE DIFF. We started off assuming shims stay with the housing and that does not work. There was also doubt that the M30 axles were the exact same size and we were running very short on time so we reused the stock axles for the time being. The flanges were different in size/ construction. We'll try to get those in some other time. They are clearly much beefier than the 200SX stuff and the bolt pattern is identical.

Result - every bit of slop & noise I was experiencing is gone. The car is really smooth and quiet at all speeds. Once I've put a few miles on it I'll test it out in the rain to see what happens.

See below, 200SX open diff...you can also see the MMR diff mount installed behind..

M30 mystery diff, sorry, bad angle...

The ungodly mess...

Is the m30 differential limited slip (lsd)?

Not to be a smartass but why else would they go through the pain of swapping unless it was an upgrade the only upgrade that would be worth is having two spinning wheels. Although I can see somone wanting a differential that is simply stronger.. so Idk... lol nvm

To my knowledge the M30 was never available with a LSD.

I'm assumming the s12 diff was bad or something.  No real upgrade in swapping to the m30 diff, especially if your not using it's slightly lower gearing.

If you look at the photo of the M30 housing, she be an LSD, I'm assuming a viscous.
The enclosed carrier is a bit of a giveaway.

Also he said he's gonna test it out in the rain, why would you do that if it was still an open?

I was gonna say, the housing did look like an LSD unit, and as Ozchuck so wisely assumed viscous- like most other Nissan stock LSD units.

Another thing, I thought the SE V6 was a 3.7:1, thus making the M30 swap now dual purpose. LSD and lower gear ratio.

Except for where he explicitly stated that he had to change the ring gear over, retaining original gears

OK guys. I can't stand it anymore. I have no pictures of the 2 wheel burnout & all that I know everyone will want to see, but it'll be here soon.

It rained like crazy here in Charlotte last week (finally, we are in a bad drought). The car did great. I'm still shy of beating on this thing only being a couple hundred miles into the engine rebuild & all. Around corners @ full throttle I had what I considered to be very very good traction. The SE is not a really powerfull car as-is so getting the tail end out without throwing the car all over the road was not happening. All I've done to the suspension so far is struts & shocks, so we are still a little clunky and I don't want to F up my new wheels.

On to the burnout. Sorry no pics, I'll have them soon. Both wheels lock up instantly. 100% LSD/locker/posi/helical or whatever you like to call it. Choose your poison.

So, did the M30 come with LSD? I don't know. Infiniti of Charlotte says yes to the VIN # (JNKHF14C5MT020128) for the donor car. They even have a replacement part in stock that they call an LSD. Now reality check here, ANYTHING anyone says about a 15 year old obsolete car with limited factory support is little more than hearsay, even the factory. I'm sure of this. But I'm also sure I have a JDM replacement in my SE that is an upgrade and didn't cost me a grand.

It's also been suggested that this M30 diff is an upgrade that someone swapped into the M30 aftermarket. I'm sure that's a possibility, but seems very unlikely. Automatic transmission, not really a big performer. The people that drive those things just don't seem like the type. Then there's the fact that it showed up in a junkyard. None of us would let that happen, so why would some one that spent that amount of effort on an M30 let that happen?

Then there's the possibility that someone figured out how to special order the M30 with that diff. Again, I don't know.

So back to the actual application. I really thought that the final ratio of the stock SE was 3.9. I've been corrected here as a 3.7. I know the ratio on this M30 diff is 3.917 by counting the teeth (47:12). So if the pinion is the same laying length it would be possible to get the 3.917 in our cars. So does anyone have a length dimension on a stock SE pinion? If I can verify that it will work we can get back into this, change the ratio & go for those M30 axles that I put brand new boots on and didn't use. Those axles are BEEFY.

neat build i guess. keep us informed on the further upgrades. i know nothing about our differentials, but i know i will probably be upgrading mine in the future as well.

good luck bud

Nope sorry, you were correct all along. The R200 in the SE was a 3.9:1. Thats my fault, I wasn't thinkin right.

Could anyone confirm if the m30s came standard with lsd? I happen to know where one is and i could get it for cheap. Lemme know.

Try getting the VIN and going to an Infiniti dealership and ask the question. If you can get them to part just the internals (that's all you can use on an S12 anyway without messing with your drive shaft) you can compare to the picture above.

i ended up having the guys at the junkyard where the car was, lift the 91 M30 into the air so i could spin the wheel.  And sadly it was an open diff.  I will keep looking though. So, i'm going to assume that a lsd diff was an option on the m30's.

My 91 M30 is without a doubt open diff.  There is a 92 M30 at the junkyard though i could look at.  I'm going to look into whether or not it has an LSD or not.  I'll use the "spin the tires" method and find out the easy way...

mine has a vlsd.

and so has everyvone i have seen pictures of the internals of.

brewster240mine has a vlsd.

and so has everyvone i have seen pictures of the internals of.

m30.

pay attention.

actuall(since m30 is one of my fav cars) the m30 is a bit more underrated than the cressida, but it has far more aftermarket than what you think, i do beleive it came with lsd for two years(im prob wrong) but i think its diff is interchangable with the j30 and.....

anyways there is a whole club dedicated to m30's look em up they can tell you what you need to know. oh, and what became of the car??

the website is f31club.com

and there is not much in the way of aftermarket for them. i have one of the most modified m30's in america(not saying much), and its all parts from z32's and 240sx's.

nothing on my car was made for m30.