M56 with an M37 rear differential

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madmanpauly
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M56 with an M37 rear differential

Postby madmanpauly » Wed Mar 11, 2020 11:31 am

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!


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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » 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

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armybrat
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Re: M56 with an M37 rear differential

Postby armybrat » Wed Mar 11, 2020 2:54 pm

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.

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Re: What to expect while doing the job

Postby EdBwoy » Wed Mar 11, 2020 6:26 pm

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.

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armybrat
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Re: M56 with an M37 rear differential

Postby armybrat » Thu Mar 12, 2020 4:13 am

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?

madmanpauly
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Re: M56 with an M37 rear differential

Postby madmanpauly » Thu Mar 12, 2020 6:47 am

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.

Yoda's Master
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Re: M56 with an M37 rear differential

Postby Yoda's Master » Fri Mar 13, 2020 8:54 pm

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

madmanpauly
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Re: M56 with an M37 rear differential

Postby madmanpauly » Sat Mar 14, 2020 4:08 am

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.

Yoda's Master
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Re: M56 with an M37 rear differential

Postby Yoda's Master » Sat Mar 14, 2020 2:46 pm

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

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » Mon Mar 23, 2020 4:13 pm

Image

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?

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » Mon Mar 23, 2020 4:41 pm

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

M56 Tone Ring tooth count from RockAuto
Image

G37 tone ring tooth count from Z1 motorsports
Image

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
Image

Who wants to be the guinea pig? LOL

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » Mon Mar 23, 2020 4:44 pm

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

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » 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!

Yoda's Master
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Re: M56 with an M37 rear differential

Postby Yoda's Master » Mon Mar 23, 2020 7:08 pm

ken in az wrote:
Mon Mar 23, 2020 4:13 pm
Image

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.

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » 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.

Yoda's Master
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Re: M56 with an M37 rear differential

Postby Yoda's Master » Mon Mar 23, 2020 8:34 pm

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.

madmanpauly
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Re: M56 with an M37 rear differential

Postby madmanpauly » Wed Mar 25, 2020 8:42 am

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?

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ken in az
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Re: M56 with an M37 rear differential

Postby ken in az » 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.

Yoda's Master
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Re: M56 with an M37 rear differential

Postby Yoda's Master » Thu Mar 26, 2020 8:56 pm

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).


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