Hello,

I'm thinking about swapping my M56 differential with a 2.611 ratio for an M37 differential with a 3.357 ratio. I see where you can get the entire carrier asssembly on ebay for around $200. Mechanically it doesn't seem to bad but I don't know what kind of codes this may produce. The M37 diffy should be able to handle the additional HP right? Has anyone ever done this or anything like this? What could I expect - other than seriously increased low end pull!

I did this with my old M45 except it was with a g37 rear diff that had VLSD.

Made a huge difference in acceleration and actually increased my fuel economy in city driving. Highway mpg dropped pretty significantly 2-3mpg.

No codes tripped, car drove great. Traction Control and stability control still worked with no problems. Speedometer on dash read the same accurate mph.

Only problem I had was with the cruise control. It would not set any higher than 64mph. My reasoning for this is because the cruise control works off the output shaft speed sensor in the transmission, which would read that the car is traveling much faster than wheel speed.

At the time cruise control was more important to me than ETs at the drag strip, I swapped back in the stock diff.

If I were you i would look for a g37 diff with LSD. The LSD would be the only reason I change gear ratios going forward. Made such a large impact on driving fun.

PS - I haven't updated my sig in a while, I have a 2011 M56 S now

I found this thread about a similar swap:
2004-fx35-awd-3-69-rear-differential-in ... 17983.html

Might pull a few codes.

Your gas mileage will also suffer, as you will be turning about 28% higher RPM's across all gears, just a thought if yours is a daily driver.

Fair warning. A diff job on the Y51 is a little more complex than on older RWD Nissans.

The previous generation M had its main axles bolted to output shafts(mini axle stubs) attached to the diff. The M56 & M37 use CV-axles that pop in/out of the diff like a FWD car.

That's conceptually nice and harmless, but it adds just a little bit of complexity in diff or axle removal because all of them have to be lowered together (but don't bend them too much). Obviously, this isn't a big issue for people with access to a lift & trans jack, but not fun for the average weekend warrior on jackstands.

Also, if you get rust in your area, better start spraying PB blaster today. Cutting & drilling exhaust components takes out a great deal of joy from the differential job.

ken in az wrote: ↑

Wed Mar 11, 2020 2:50 pm

I did this with my old M45 except it was with a g37 rear diff that had VLSD.

Made a huge difference in acceleration and actually increased my fuel economy in city driving. Highway mpg dropped pretty significantly 2-3mpg.

No codes tripped, car drove great. Traction Control and stability control still worked with no problems. Speedometer on dash read the same accurate mph.

Only problem I had was with the cruise control. It would not set any higher than 64mph. My reasoning for this is because the cruise control works off the output shaft speed sensor in the transmission, which would read that the car is traveling much faster than wheel speed.

At the time cruise control was more important to me than ETs at the drag strip, I swapped back in the stock diff.

If I were you i would look for a g37 diff with LSD. The LSD would be the only reason I change gear ratios going forward. Made such a large impact on driving fun.

PS - I haven't updated my sig in a while, I have a 2011 M56 S now

Based on this I am guessing that if you have the AWD model you would have to swap both diffs, if that's possible?

I'm driving a 2011 M56S not AWD so I only have the rear end to worry about. It seems like a straight forward swap, just gonna be a PITA. I'll read more about the G37 swap and then decide if I want to take on that big of a project. I like the power of the M56 but it could use a bit more on the low end. I was thinking this might be a good option. Thanks for the feedback, I'll put some more thought to it.

The G37/370z drive shaft bolting pattern is different so it wouldn't work. 4 bolts vs 3 bolts

Understood, we are talking about an m56/m37 swap. There’s information about a g37 swap that may be similar. It’s not the same but it should give me an idea of what’s involved for reference.

Just pointing out there's no point in reading up on the g37 swap since it wouldn't work anyways.

This one is 3 bolt like ours. I'm trying to find out how many teeth are on the Tone Ring of the axle stub and to see if the sensor is compatible with our car. I'm 99% sure it is, but if the tone ring has a different number of teeth, then it will throw off the Stability Control/ABS/HICAS all kinds of stuff.

Anyone have access to a G37 axle stub to count the tone ring?

Did some looking online - looks like the Tone rings are both 48 tooth which is perfect

M56 Tone Ring tooth count from RockAuto


G37 tone ring tooth count from Z1 motorsports


Being that the track width is only 0.4" difference between the two cars, the G37 cv axles should fit since they both have 32 spline outers.

G37 32 spline outer per RockAuto


Who wants to be the guinea pig? LOL

My Bad - the rear cover on the differential is different. You would need an M37 Rear Diff cover for the swap to bolt in.

Well - looks like it's gonna be me. This Quarantine must have gotten to me lol

Found a low mile g37 diff on Ebay along with an M37 rear cover, then ordered half shafts from RockAuto

I'll keep y'all posted!

ken in az wrote: ↑

Mon Mar 23, 2020 4:13 pm

This one is 3 bolt like ours. I'm trying to find out how many teeth are on the Tone Ring of the axle stub and to see if the sensor is compatible with our car. I'm 99% sure it is, but if the tone ring has a different number of teeth, then it will throw off the Stability Control/ABS/HICAS all kinds of stuff.

Anyone have access to a G37 axle stub to count the tone ring?

That's not a g37 diff. The g37 has 4 bolt holes.
That is the PN of that diff?

Edit: Alright, i take that back. Looks like the AT diff is different than the MT diff.

I think it's the sedan vs the coupe is the difference. At least that's what I was seeing.

ken in az wrote: ↑

Mon Mar 23, 2020 7:49 pm

I think it's the sedan vs the coupe is the difference. At least that's what I was seeing.

Nah, i checked both coupe and sedan. The MT is 4 bolts and AT is 3 bolts for both types.

If you're going to try, then you need to buy the 2 washers that are installed between the forward bushing and subframe, If the mounting holes are even in the same location. The mounting bolts and bottom washers are the same between both.
The P/N is 55474AG011 - G37/370z
The PN for the M56 is 554741MA1B

Different diff mounts use different hardware.

One thing you need to watch out for is buying a sports diff or non-sports diff.
Sports: 38301EH38C
Non-sports: 38301EG38C

Biggest difference are:
Sports: LSD
N/S: Open Diff
Also sports and n/s have different axles. I believe sports have threaded axles and n/s has threaded stub shafts to connect the axles to the diff.

ken in az wrote: ↑

Mon Mar 23, 2020 5:56 pm

Well - looks like it's gonna be me. This Quarantine must have gotten to me lol

Found a low mile g37 diff on Ebay along with an M37 rear cover, then ordered half shafts from RockAuto

I'll keep y'all posted!

After looking closely at this, I don't have the right garage setup to pull this off without getting crazy. Looks like it's gonna be you amigo! I'm very curious how this goes and will be following. I'm a bit confused though, are you using the M37 rear diff or the G37 rear diff. Both have been discussed but it looks like you are putting a G37 diffy into the M56. Correct?

Yes - it is a G37 VLSD unit that is a 3.36 ratio, same ratio as the M37. The VLSD isn't ideal, but it is way better than the open differentials that the M37 and M56 have.

If I've done my homework right, I should be good enough for 125mph in 4th gear, which is perfect for the 1/4 mi with about 500ish hp (nitrous shhhh)

My axles came today, and I think I messed up on the order because one axles has a threaded flange and the other is smooth. I need to wait to see what my Stub Axle flanges look like before I know what to do with them.

VLSD stubs are smooth. the bolts thread onto the axles on both axles. You bought one sports axle (threaded) and one non sports axle (smooth).

ken in az wrote: ↑

Thu Mar 26, 2020 8:37 pm

Yes - it is a G37 VLSD unit that is a 3.36 ratio, same ratio as the M37. The VLSD isn't ideal, but it is way better than the open differentials that the M37 and M56 have.

If I've done my homework right, I should be good enough for 125mph in 4th gear, which is perfect for the 1/4 mi with about 500ish hp (nitrous shhhh)

My axles came today, and I think I messed up on the order because one axles has a threaded flange and the other is smooth. I need to wait to see what my Stub Axle flanges look like before I know what to do with them.

Any updates on this? I was thinking the same as you for the chemical supercharger! These would be low 11 second cars with some traction and a 100 shot.

I have the axles and diff sitting right here in my garage. I'm in the process of moving garages at the moment to clear up some more space, so I don't see them going on anytime soon. Plus I still need to get my headers and Exhaust tuned but UpRev/Admintuning. That should happen later in August when I can get some dyno time.

Maybe in September ish timeframe unless I get a wild hair and do it sooner.

Did you say you have a nitrous setup? Got details?

No nitrous for me - I might be boosting it with a mid-mount turbo and stealing the high pressure fuel pump upgrade from Harrop to over 600whp

But all in good time.

Hmm, interesting...

Update on the rear differential swap to a g37 diff with VLSD and 3.357 ratio. Right now I am at a standstill. The g37 front mounts are narrower than the m56 by about an inch or so.

I'm gonna have to figure out an alternative before this swap can happen.

Reviving this thread because I have swapped out differentials and am trying to come up with a solution for the loss of cruise control and codes that come up from it.

Specifically the Vehicle Speed Sensor which I believe is the same thing as the transmission output speed sensor. I assumed the ECU was receiving the now faster speed signal from the sensors on either side of the rear of the differential. I designed new tone rings with less teeth proportionate to the difference in speed between the ABS speed sensors and the VSS.....

Well that didn't work... Day of wrenching for nothing but to have to do it again and put the original tone rings back on. I soon found that the tone rings on the rear axles provide data to the ABS system to determine the rear wheel speed and was not the VSS.

So that leaves one sensor as the culprit and that is the Transmission Output Speed Sensor... So how do we fix this?

Ideas: For reference the Output Speed reads approximately 23% higher than the wheel speed.

1. Ideal Fix: ECU Programming modification through Consult or UpRev. Is either one possible?

2. Electronic device to detect signal from Output Speed Sensor, alter the signal to compensate for the difference in speed, and output the altered signal to the ECU. Can't find anything online except pulse multiplier dividers but they factors of multiplication and division were 2 x 3 x 4 x or /2 /3 /4 , etc.. so no way to find tune the frequency of the pulses. An Arduino may be able to serve the purpose giving the ability to precisely alter the signal. I know the wheel speed sensors are 5 Volt Square Wave Pulses. I don't know what the Output Speed Sensor is but I assume it's the same. I will have to hook an oscilloscope up to it and see what kind of signal it's producing.

3. ??? Worst case would be redesigned tone ring with proportionate reduction in teeth. But that would be a lot of work requiring tearing into the transmission and possibly lots of fabrication if it can even be done.

Can anyone with more knowledge on this kind of stuff chime in?

BTW... I highly recommend the differential mod... Brings the car to life! Roasting tires and ghosting Scats!

You've got a major problem, because the cluster will throw codes if you alter the OSS signal too. On ABS-equipped Nissans and Infinitis, the cluster expects to see the VSS signal from the ABS and the VSS signal from the tranny within about 5% of one another. So you'll need to change all 4 ABS tone rings and use an electronic adaptor to alter the OSS output. Without reconciling both signals, your cruise will never work.

Ok, thank you for the clarification...

Why would I need modified tone rings if I was able to modify the OSS signal to be within the 5% threshold?

See image below (This is a photo I took of the data, prior to modifying the tone rings on the rear axles, I was reading from all 4 ABS Sensors, Vehicle Speed from the ECU, and OSS which is the reading on the bottom right of the photo.)