I have Ford L8000, 7.8 Turbo (non intercooler), with Rockwell SQ-100P rear diff with 6.14 gears. Door tag rating is 39,000#. It has the FS-5005 5 Speed transmission. I have 11R22.5 tires.

With the final gear ratio of 1.0 and rear end gear at 6.14, the estimated top speed is about 50 mph at 2500 RPM.

I have done some calc and swapping the rear end gear to 4.88 will increase that speed to 63 MPH.

I have done several gear swaps in the past in a race car so doing the swap is not a problem.

Thought? Where is a good supplier for gears?

 

I just got a air ride axle swapped into my F-700.
My gears were changed from a 4.10 to 3.58 . I bought a used set of gears from Anderson bros in Portland OR. A lot of these big truck axles look like a over sized 9 inch. Much simpler than you might think.

I also not over look ebay as well. and don't forget to do some homework to make sure there isn't a carrier break between those two ratios for your rear end.