I have recently purchased a very clean 1979 F250 with only 85,000 miles on it. I get only 10 mpg and thinking I can increase it with a different rear axle gear ratio? There are two "lines" of numbers on the tag bolted to the rear axle cover and I'm not sure what they mean. First Line reads: 3 73 D9TA BTB. Second Line reads: 603900-21 LS. The truck has a 351 (2 barrel), and C6 transmission. Can anyone tell me what gear ratio I have? What are the rpm's at different gear ratios? I do not plan on doing much real heavy towing; however may, so how would this affect towing? What gear ratio should I change it to? Thanks

 

It looks like 3.73's to me.

This info should be on the bottom line though.

Great ratio for towing a boat out of a lake,a trailer in the bush, but a real gas slurper on the hwy.

351M's are gutless with 146hp.
The 2 bbl helps give you the torque so stay with that.

If it was me I would go to 3.25:1


Have a look on Page 3 of the site for the buck tag info.

http://66.96.130.106/archives/2002/0...ch/index.shtml