Hey guys! Just bought an 08 F450 diesel 6.4L dually. Love the truck cept for 1 thing. Seems like trans shifts fine thru all 5 gears but rpms are at 3100-3200 at 80mph. Seems like either there shud be 1 more gear or stock rear gearing is just not right! Any advise to what should be done?

 

Welcome to the world of an F450 with a 4.88:1 axle ratio. That is what it takes to move the load that the F450 is rated to move.

You can change the axle ratio, but it will lower the load that the truck can move.

 

Thx! Wat gearing would be recommended so i can cruise at 80 n have no more than say 1800-2100rpms? And just how much would load max reduce?

 

You'll need a 3.20:1 gear to be at 2100 RPM at 80 MPH. I've never tested an F450 with that ridiculous of a gear ratio because it wouldn't have any load capacity. Plus, I don't think anyone makes a ratio near that for your axle.

Do you need something to carry/tow a large load, or a sports car to zip up and down the freeway at 80 MPH? Those two uses are mutually exclusive.

 

The cleanest, possibly most expensive, fix:

Gear Vendors Under/Overdrive Ford Truck-Car-Van 2-Wheel Drive 4-Speed and 5-Speed Automatics.

 

I installed 3.73 gears in my 08 F450. I haul a lance camper and pull a 20' inclosed trailer.