Originally Posted by Grigg
I too think the rear axle it's self is not a weak link, it's the math and the gear ratio that will hold you back.

Here's a gear calculator for you to play with
http://www.onlineconversion.com/bigger_tires.htm

In my experience the 55 model 235 in my 1 ton ran well at 2,500 rpm or thereabouts, anything over that just wasted fuel, it would run faster but didn't seem as happy.

So what transmission (overdrive) ratio, axle ratio, tire size, and engine RPM do you need to go the speed you want? And then will the engine actually pull that?

I feel that my 1 ton would be great with 4.10 gears, 33.5" tires, the original 4 speed, and the newer 235, but any faster gears and the engine lacks power.
Most recently I ran 4.56, which is great for a working truck on short trips, 50-55 mph but empty trips over an hour and the one step faster gears would be welcome.

Grigg

I wasn't concerned about the axle itself, rather if the entire 3rd member would explode turning that fast, or more importantly, would I throw a drive shaft spinning that fast.

What I envision is to do your P30 swap without changing the front end (was hoping to just change 3rd member but still doubting availabiltiy of 4:10's for that). I'd try the disk brake conversion like in the other post and get it up to speed to see how it handles before changing the whole front end. If the 4BT mostly drops right in, as you inferred, then I'd probably do that to get the torque I need for the SM420. I am not opposed to change the transmission, however I do like the PTO hookup that drives my hydraulics for the dump bed. Maybe with the 4.10 gears, 33" tires, and the 4BT I could get to 60 (calculator). Running 2500 RPM I could get close to 60, and hopefully the 4BT would have enough torque to pull through the wide spaced 2-3-4 gears of the SM420.

Does that sound about right?

Thank you

Last edited by Skybum; 01/10/2010 3:42 PM.