My '78 F250(351M 2WD) currently has the borg warner T18. Its geared much too low for anything other than pulling down a small house, and 70mph? at 4000rpm is not so good for gas mileage. The teeth on the mainshaft that mate with the speedo gear have also been damaged somehow so no speedo. I would like to replace the trans with one thats geared higher(overdrive?) and would greatly appreciate any suggestions.

 

There really isn't anything that won't be a big project. You can use a ZF 5spd out of a never F250 or bigger with a 460 but it will require a lot of fabrication and different length drive shaft. You might want to check your rear end ratio, you can go with a higher ratio there to get you rpms down and use that super low first to get her off the line. I plugged 70mph at 4k and with 29" tires into the calculator and it came up with a 4.93 rear gear so I am guessing you are actually going a lot faster than 70 because that is a lot lower than any thing Ford ever put in these trucks, you probably have a 4.10 and with that you are doing 84 at 4k so you might want to get that speedo fixed. Just for example if you went with 3.55 which I have in my 79 F250 and it goes 70 at 2600rpms, or if you went even higher like 2.73 with 29 tires it would put you at 2200. I don't know what tires you are running I just used 29 as kind of an average for a 2x4 but as the transmission is such a big project and gears would be so much cheaper I figured I would throw the idea out there, you can also cheat a little by running bigger tires.
-Johnboy

 

Where would be a good place to find a high rear gear? I have the Dana 60.

 

Randys ring and pinion is pretty good, you will most likely have to swap carriers too but that isn't a big deal. You will just have to call around to find an installer unless you can do it yourself.
-Johnboy