Swap rear ends or transmission?

yes, about 20% lower 14.4 vs 12.1 ratio. And 8% faster in high gear.
Smaller ratio steps and no overlapping gears. 15 speed has only 12 succesive gears.

 

Think 15 actually has lower overall gear in deep reduction, but bigger steps and overlapping ratios. 3.55 40k axles in dump truck off road with gobs of torque... You will find your weak link!

 

I agree on the weak link remark.

This is the info I have from Eaton for RTO15715 (12.1 in Deep Reduction 1):



For 18 speed (14.4 in LowLow):

 

I had to look at a chart... I stand corrected and loosing my memory. @KVB posted correct ratio. I must of been thinking of direct drive 15 or just had my head up my arse! Tried to post link to charts, but was unable to.

 

I think he's already snapped a few yokes off IIRC.

 

The model you posted is a 15 speed. It has deep reduction giving lower ratio in low side.

 

Main box I believe is the same as a 10 speed. Aux section is a 3 speed instead of a 2 speed. Starting in the basement and shifting up you'd go:


Deep reduction: 1, 2, 3, 4, 5

Low range: 4, 5

High range: 1, 2, 3, 4, 5


Reason you go from 5th deep reduction to 4th in low range is that 1st through 3rd in low range overlap the deep reduction gears.

 

3.55 off road is just to high speed no matter what trans especially if on 11/24.5 rubber. You really need 390 or 410 gears.