90 4x4 auto trans setup ... difference in ratio 4H to 4L

[Keithnh]

Have not spent alot of time under my 170K truck ... it just runs and works and sounds nice with the Flowmaster that has seen 4 exhaust systems and is still good. Let a friend use it and he put it in 4L trying to get out of a snowbank and couldnt understand why I was pissed he was spinning the wheels rocking back and forth trying to get out. He was aggravated wanting to get it down to where his plow truck was stuck and was spinning them possibly up to 3000ish rpm. I hollered and said "get out of my truck", got in, put it in 4H, drove forward to get a small run and backed out through the snow without spinning. Was trying to explain to him that 4L is not for getting out of a slick spot but he couldnt understand. Was wanting to be able to say " when you switch to 4L the gear ratio changes from 3.41 to like 5.16, once you break traction the wheel and entire drive train will spin way faster as if you were going 60mph instead of 30" but I dont really know what the ratio difference is. Wondering if anyone here might know??

 

Noticed now I have a clunking when actually moving in reverse 4H, so something is broke.

[arcasey]

It really depends on the transfer case. Different cases have different ratios. I believe the standard cases that came on that series truck was around 2.7:1 in low range. You are partially correct that somethings will spin faster. When you switch to 4LO, your transmission and motor will still spin at the same speed while your driveshafts speeds will be reduced by the ratio of the transfer case. What this means is that your drive shafts, differentials, and tires will spin slower than normal when in low range. There are some really informative 3-D animation videos on youtube that explain what actually happens inside the transfer case.