I have a 77 f250 with 351M c/6 tranny with 16.5" wheels. The problem I have is the gear ratio sucks in my truck. I drive 55 MPH and the motor revs like crazy. What type of rear end is used in these trucks I have the original build sheet from the Ontario Ford truck plant and it says that it has "optional ratio axle" It was a cemetery work truck. So there are not many miles on it, but it is a HOG on gas especially at 69 cents a litre (over 3bucks a gallon)
Can I use gears from a 9"? I think that I probably have upwards of 3.73:1?????
I would like to find 3's or even lower if possible but I am not sure what rear axle I have. (My brother in law has 2 79 ford 1/2 ton trucks and I could probably get gears from him if they would work)
I don't want to change rear axles to 15" 5 bolts because I'd have to change the front end too and I don't even want to try that

Thanks
Stoney

 

It sounds like you have at least 4.10 gears in your axles. 9" will not work, you should have a Dana 60 axle in your F250. The cost of changing gears in your truck will buy a lot of fuel! I suggest either leaving it alone, or finding someone who has 3.55 gears and will just swap axles to get your low gearing. Another thought, bigger tires will help tame those gears down some!

Nathan