Hey folks, I have a 75 CC, 2wd, 390, manual 4speed w/ granny and 4.10 rear end gears. My tires are 29.5 tall so it don't take long till the RPMs are making me want to shift to fifth gear which I don't have. I found a posi with 3.5 something rear end gears. Would that be to much of a jump. It will be towing a 22ft camp trailer during the summer months.
For towing kinda heavy, I'd personally go with a bit taller tire and keep the 4.10's. With 31" or 32" tires it should handle speeds up to 70 or so and still tow well. Yes it the engine will spin a bit but can take it fine. My 78/400/4.10 does fine at 70 with 31" tires. I'm running 245/75/16 10 PR on steel wheels. Pretty close to 9.50x16.5" which was on the truck before the switch to 16's.
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. Ford® is a registered trademark of the Ford Motor Company.