Reduction gear options for a Sierra: pros and cons

[gwagensteve]

Good call.

Steve.

[davidsuzuki]

Ok, so with 6.5 transfer gears and some reinforcements for the transfer case mounting (such as that EOS cradle) I will have a reliable, trouble free setup??

Steve I've been putting some figures through that gear calculator -- http://www.lepayne.com/gears.html (thanks jono165) and can't work out why I would lose a gear offroad with the 4.1/4.1 setup??

[jonfromhamilton]

It's all about the crawling

[mika]

i was running 6.5's with stock 3.7 diff ratio and just some reinforcements to the long side transfer arm which included a small bracket to pickup an extra 2 bolts on the transfer case. No issues with very agressive 33x12.5 on beadlocks on 10 odd hard trips. Keeping the genuine stock rubber mounts or something similar that is stretchy helps to reduce shock load to the transfer but unless you are a very abusive driver you should have no trouble on 31's. Heaps of guys run that setup.

[lbzook]

I've got 6.5's on 31's and stock diff gears and my transfer case mounts are holing up fine, I did however trash a passenger engine mount within 5 trips though

[gwagensteve]

Ok, so with 6.5 transfer gears and some reinforcements for the transfer case mounting (such as that EOS cradle) I will have a reliable, trouble free setup??

Steve I've been putting some figures through that gear calculator -- http://www.lepayne.com/gears.html (thanks jono165) and can't work out why I would lose a gear offroad with the 4.1/4.1 setup??

Crawl ratio isn't as low.

Crawl ratio is 1st gear X low range X axle gear

With 4.1/4.1 it's 61:1
With 6.5's alone it's 88:1

60:1 is fine, but it's the tallest crawl ratio that feels good. In my book, there's no point gearing a sierra to achieve a crawl ratio taller than 60:1, unless it's automatic.

with 88:1 you can always slow down enough to feel in control, and 4th low is a really usable gear for muddy hills etc.

Steve.