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Discussion Starter · #1 ·
Check these Final Drive Ratio\'s

Ok, I just wanted to post about what I just figured out and thought maybe I should share it with everyone else. As most of you know I am well on my way of building a truck for Truck Pulling. Anyway, last weekend I picked up a SM456 and a Np205 and I was just doing the math to find out what final drive ratio's I will be running at whith the combo and having 4:10's in the rear end.

I can't belive how close two of the ratios are. If I pull in 1st(Lo)and have the T-case in Hi the final ratio will be 26.85:1
Now if I pull in 1st gear with the Tcase in Lo gear the final drive ratio will be 29.06:1

I am just amazed that both these ratios are so close together and thats the main reason guys I know can pull in either gear depending on the track and also why guys that I know that do mudding run in either or gear starting out.

Now if I were to run in Lo and Lo my gearing would be 53:1 which for what I am doing is WAY to low because I can't shift gears and the next thing I would know is magically there would be 8 holes in my hood/wwwthreads_images/icons/wink.gif

Anyway, just thought I would point this out to you all that have this combo or are intrested in it. So far from what I see and what I have heard...I love it.

Ryan

93 GMC Yukon
Chevy SuperStock 4x4 Truck Puller
Great Lakes Truck & Tractor Pulling Association
http://www.greatlakespull.com
 

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Re: Check these Final Drive Ratio\'s

I love that combo, I couldn't imagine wheeling without that granny gear.

The only thing that would be really, really nice, would be an overdrive gear for the highway.

Ugly 78 GMC 3/4T Camp. Spec. 350/465/205; needs major work.
 
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Re: Check these Final Drive Ratio\'s

Ryan,
How did you calculate those ratio's. The first two where you compare tranny in first gear and then switch the transfer case from high to low (using same gear in tranny). There should be approximately 1.96:1 (the standard gear reduction of the NP205) difference, your difference is 1.08:1. Did I miss something?
 

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Discussion Starter · #4 ·
Re: Check these Final Drive Ratio\'s

Um....I think I messed up in the way I stated it. The first ratio was with the Trany in LO where the 2nd was with the trany in 1st(2nd gear) because the shift leaver on the SM456 goes like this L-1-2-3-R

Ryan

93 GMC Yukon
Chevy SuperStock 4x4 Truck Puller
Great Lakes Truck & Tractor Pulling Association
http://www.greatlakespull.com
 
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