Front axle gear ratio

Redbaron73

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I am confused by the different gear ratio in the wrangler 4wd system. I have a stock drive train on MY*JLUR.

I understand the rear has a 4.1 gear ratio, and the transfer case has a 4:1 LO gear.

I know that the front axle is a M210, but what gear ratio is in this? Does it even relate to the transfer case gear?

When I re-gear in the future, am I only changing the rear axle (say to 4.88 for 37's) or am I also making changes to the transfer case and/or front axle?





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Arterius2

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I am confused by the different gear ratio in the wrangler 4wd system. I have a stock drive train on MY*JLUR.

I understand the rear has a 4.1 gear ratio, and the transfer case has a 4:1 LO gear.

I know that the front axle is a M210, but what gear ratio is in this? Does it even relate to the transfer case gear?

When I re-gear in the future, am I only changing the rear axle (say to 4.88 for 37's) or am I also making changes to the transfer case and/or front axle?
4.1 same as the rear. And No this is not related to your transfer case low range ratio. But it does help with the crawl ratio when you are in 4Lo. Otherwise your transfer case is in 1:1

So basically your crawl ratio = transmission gear ratio x axle gear ratio (4.1) x transfer case ratio (4 or 1)

When you regear you have to change both the front AND rear axle gear ratios.
 

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I am confused by the different gear ratio in the wrangler 4wd system. I have a stock drive train on MY*JLUR.

I understand the rear has a 4.1 gear ratio, and the transfer case has a 4:1 LO gear.

I know that the front axle is a M210, but what gear ratio is in this? Does it even relate to the transfer case gear?

When I re-gear in the future, am I only changing the rear axle (say to 4.88 for 37's) or am I also making changes to the transfer case and/or front axle?
No, your front and rear gear ratio will always be the same, otherwise your Jeep will run funny. Actually funny will be the understatement, if you have a taller front gear ratio, you can pop a wheelie in 4H.
 

nerubi

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No, your front and rear gear ratio will always be the same, otherwise your Jeep will run funny. Actually funny will be the understatement, if you have a taller front gear ratio, you can pop a wheelie in 4H.
Really, a wheelie? I know what project I have in mind starting tomorrow morning.:rock:
 

D60

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No, your front and rear gear ratio will always be the same, otherwise your Jeep will run funny. Actually funny will be the understatement, if you have a taller front gear ratio, you can pop a wheelie in 4H.
Yep or you'll just grenade the transfer case ;)

OP, when in 4wd (either H or L) the front and rear outputs are tied together by a fixed chain. There is no differential in the t-case or allowance for difference in rotation of front and rear (note this is the primary distinction between part-time 4WD like most of our JL's and full-time 4WD aka AWD) so the t-case will attempt to force both front and rear driveshafts to spin the same, no matter what.

Tiny variations are absorbed thru drivetrain wind-up, the tires, the differentials in the axles etc....but a difference as significant as a completely different ratio in front and rear diffs will cause substantial issues in short order. This is also why you want all 4 tires to be the same size - different size tires effectively change your gear ratio.

Note it's completely common for OEM to use 3.54/3.55 or 4.10/4.11 in many vehicles. This is fine and is not a strategic choice but USUALLY just has to do with one axle being corporate (like a Ford 8.8) and one being built by an independent like Dana Spicer
 
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Redbaron73

Redbaron73

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Yep or you'll just grenade the transfer case ;)

OP, when in 4wd (either H or L) the front and rear outputs are tied together by a fixed chain. There is no differential in the t-case or allowance for difference in rotation of front and rear (note this is the primary distinction between part-time 4WD like most of our JL's and full-time 4WD aka AWD) so the t-case will attempt to force both front and rear driveshafts to spin the same, no matter what.
How does the 4L 4:1 ratio come into play. My understanding is this in the transfer case. Is the gear on the fixed chain that ties the front/rear together sized to give the 4:1 ratio?

Tiny variations are absorbed thru drivetrain wind-up, the tires, the differentials in the axles etc....but a difference as significant as a completely different ratio in front and rear diffs will cause substantial issues in short order. This is also why you want all 4 tires to be the same size - different size tires effectively change your gear ratio.

Note it's completely common for OEM to use 3.54/3.55 or 4.10/4.11 in many vehicles. This is fine and is not a strategic choice but USUALLY just has to do with one axle being corporate (like a Ford 8.8) and one being built by an independent like Dana Spicer
This brings up an interesting distinction I have seen on the JLUR - the front is a M210 and the rear is an M220. I assume they are geared identical, being both DANA. Besides the physical offset of the pumpkin, is there anything substantially different between these two axles?
 

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How does the 4L 4:1 ratio come into play. My understanding is this in the transfer case. Is the gear on the fixed chain that ties the front/rear together sized to give the 4:1 ratio?
No the chain only ties the front and rear together. The 4:1 comes from the planetary on the input.

This brings up an interesting distinction I have seen on the JLUR - the front is a M210 and the rear is an M220. I assume they are geared identical, being both DANA. Besides the physical offset of the pumpkin, is there anything substantially different between these two axles?
The front is high pinion with reverse cut gears and a 210mm ring gear diameter.

The rear is low pinion with standard cut gears and a 220mm ring gear diameter.
 
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Redbaron73

Redbaron73

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No the chain only ties the front and rear together. The 4:1 comes from the planetary on the input.



The front is high pinion with reverse cut gears and a 210mm ring gear diameter.

The rear is low pinion with standard cut gears and a 220mm ring gear diameter.
Thanks for your explanations
 

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Yep, everything first runs thru your planetaries which live in the large "bell" part of the t-case that actually bolts to the transmission (or more accurately the tailshaft housing).

In high range the planetaries are basically "dormant", doing nothing and just sending power thru 1:1. In low range a shift fork slides to activate the planetaries and you get your gear reduction of 2.72:1 or 4:1 or whatever

Note all of this happens basically immediately AFTER the transmission but BEFORE power is sent out to any of the driveshafts
 

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