Gear Change for 37's on my 392

Outrun

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If that's true I think the dana 60's were around 5,500 so that could work. I'm thinking maybe the ring gear? Don't the M220 use the same spline count as the JK Rubi 32 spline? Maybe they changed the axle shaft material? I hope so it is one of the bigger things I worry about on the 392. My JK has a dana 60 that runs 35 spline shafts because I had issues keeping the dana 44 happy in it with 37's. twisted splines and locker failure but it does have a 4:1 transfer case in it and I have pushed it at times.
I believe the difference between it and the JK one's are the new axles are more heavy duty in all areas. Ring gears and pinions are thicker along with a change in angles and how they are cut for added strength. The pumpkins and axle tubes are more reinforced/thicker. The front knuckles are much stronger. Etc.
The idea behind this was to keep strength up to allow the use of more horsepower and/or tire size increase while keeping the physical size and weight down.
There has to be someone who cut one up to prove this.





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I believe the difference between it and the JK one's are the new axles are more heavy duty in all areas. Ring gears and pinions are thicker along with a change in angles and how they are cut for added strength. The pumpkins and axle tubes are more reinforced/thicker. The front knuckles are much stronger. Etc.
The idea behind this was to keep strength up to allow the use of more horsepower and/or tire size increase while keeping the physical size and weight down.
There has to be someone who cut one up to prove this.
If you find a video of a cut up axle, I'd love to see that because I bet you are completely correct!
 

ValB

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I'm running 37x13.50's on KMC XD 231 beadlocks, and want to re-gear for the bigger heavier tires. I'm thinking 4.56's, but wondering if I should do 4.88's instead?
Thoughts?

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With a 37" and bead locks I would go with 4.88:1 I have 35" and I plan on a Spicer 4.56:1 change out.
 

supermike

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and also keep in mind, the taller the gear ratio, the smaller/weaker the pinion and ring gear teeth it gets.


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nowandthen

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Apples to oranges comment: I initially put 5.13's in my JK with Pentastar and 6 speed manual with 37's. The gears started howling after only a few hundred to few thousand miles. Tried 3 sets of 5.13's. Dropped down to 4.88's and haven't had a problem since. Likely spinning the 5.13's way too fast at 80 MPH (or more 😮 ). I think I could have gone with 4.56's instead of 4.88's and been happy. I realize most are running 8 speed auto, but for me, next Jeep, I will error on higher? Lower? gears, meaning 4.56 before 4.88 with the 8 speed automatic. My .02.
 

guarnibl

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AEV has stated 4.56's with the 6.4 and 37s.
With what 37’s though ? There are 40’s that weigh less than 35’s. 392 will handle larger tires a lot more easily — I think your right on 4.56’s lining up closest though to the original 3.73’s from factory in terms of RPM.
 

Outrun

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With what 37’s though ? There are 40’s that weigh less than 35’s. 392 will handle larger tires a lot more easily — I think your right on 4.56’s lining up closest though to the original 3.73’s from factory in terms of RPM.
That's a good question and I don't know which ones.
I think their parameters are strictly about RPM's and performance. The 392 probably doesn't care too much about weight if the axles are up to the task.
 

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