Gearing advantages?

[kauser44]

First off I'm referring to a Duramax Allison combo. Is there any advantage to running say lower ratio in the rear end and higher in the trans say 4:56 in the rear and 4th gear apposed to 3:42 in the rear and 3rd gear in the trans. The final drive is close between the too with the first option being a little faster. Does one or the other offer better mechanical advantages.

 

[zstroken]

If you can't keep the ring and pinion in it with 4.56, try the 3.42. However it will be harder on everything in the driveline ahead of the rear end(ujoint and up)

 

[kauser44]

I understand the 3:42 has a bigger pinion. But I guess what I'm after is there less of a power loss through the drive train with one or the other or is as long as the final drive is the same it doesn't matter.

 

[Sarafin]

On paper, final drive is final drive. Like zstroken said, the big difference it's where the driveline will feel the stress

 

[ikeG]

Kind of a 'pick your poison' type of thing. Like stated, 3.42s will move the stress further along the driveline. The gear mesh of 3.42s is so strong that it will virtually never break at the gear mesh, it can shear the pinion completely off and then the ring gears sends it down through the case. Which ruins case, AND ring and pinion. 4.56, etc. will solve that but will put stress on the ring/pinion teeth. Which can be R&R'd a lot cheaper/quicker than a complete housing.

 

[kauser44]

The truck I'm building is a work stock truck. It does not make enough HP to brake r&p. My thought process when I went to 4:56 and 4th gear in my old 2.6 truck was that since the trans is 1:1 the plantes and ring gears are all turning together resulting in less power loss to the ground vs using the planetarys in the trans for gear reduction in third. Is there any truth to that?

 

[CurtisEmery]

Yes direct drive will be more efficient. How much I cant say. It is also the strongest gear in and Allison trans. I would much rather break a r&p than destroy the housing like stated above.