hey guys i was just wondering what you guys run for gearing..i have 37s and plan on 40s, what do you think is better for 40s in my 76 f250..411s or 456s? i have a np435 trans. i have 411s now and with the 37s it screams going down the highway at 65.? or dont even bother gearing there wont be much of a difference

 

456 will make it worse.....

 

#1,, do you have a Tach? So you can say what "screaming" is,,, Ideally, you should be cruising 2100-2500,,, not all are the same, but as as a general rule. I had a friend, she thought her jeep was screaming at 60, when in reality, it was only at 2300 rpm's,,, to her it was wound up, just because it was loud. I have a 400/NP435 with 33's and 4.10's,,, runs a little fast, but I am ok with that because I live in the mountains and prefer the power,,, mileage is about 8-10, but that is a trade-off. I would think with 37's and 4.10's you should be just fine. Again, get a Tach and go from there!

 

I have 4.10's and 31" tires. Runs fine at 70-75 MPH. Yes... it is in the 3000+ RPM range and can take it. With your big tires, I would suggest 4.56 for decent performance and some towing ability (if that matters).

 

I have 35s and run 3.50s.. a lil doggy but OK.. the NP435 takes care of business.
3.70s would be better in my case.

Refer to the table below for ballpark RPMs for your application.

 

I have 3.50 gears on 33" tires. My set up is a little tall on purpose. I have a 300 six that doesn't want to rev very high. This creates a problem trying to maintain 25 mph through town. It surges a little trying to lug down that low. 4.11's would be fine with 40's. I've run that gear with those tires before and was pretty happy. I think 4.56s would be too steep, but that's just my opinion.