I have issues with my 95 F-superduty, I have a axle code 73 and on some lists decoding this number it lists it as a 5.13 dana while others list it as a 3. something. I know for a fact the latter cannot be right because at highway speeds 70 to 80 mph (I hot shot in texas ALOT) its turning anywhere from 3000 to 3500 rpm. theres no way in hell that kinda rpm will get me 70 to 80 mph is there?
I average about 8 to 10 mpg and my primary concern is getting that number up in the at least mid teens because my fuel bill is tearing me a new one! I am currently scouting the local u pull it lots but finding the elusive 95 F-superduty is proving to be no small feat. I have said all this to pose these questions...
( 1 ) will I have to find a 95 F-superduty with an axle code 72 to get my ratio down in the 4's or are there other year model rear ends that will interchange? bear in mind I cannot sacrifice any strength as far as the carrying capacity of the replacement rear.

(2) Is there anyone else out there who has the same vehicular identity crisis as I do? as far as I've been able to ascertain the 95 F-superduty does not bear any label such as F350 although every stinkin parts store around will diligently attempt to label it as such. if you possess this rare and noble box nose give me a shout... they say misery loves company, but more importantly you may have information that I have thus far failed to grasp.....

 

According to my Ford Service Manual axle code 73 is a Dana 80 w/5.13 gear. That axle is rated at 11,000 pounds. The only other gear I see for that axle is code 72, which is a 4.63 ratio. That is a 10% reduction in ratio/RPM so it may be worth finding one. But I do not think that will get you into the mid-teen range in MPGs.

 

Yeah, I have a '94 F-Superduty with 5.13s. They only came from Ford with 5.13 or 4.63 ratios. You'll need to either change gears or get an OD unit...
Yeah, the parts stores insist it must be an F-something Super Duty. Stand your ground, tell them to look in Medium-Duty trucks and they will find it.

 

thanks for the input guys, i love that old truck but its cost me a butt load of money as well as substantial amount of blood and sweat getting it road ready and now the only thing standing between me and the old girl making a very nice living in the hot shot business is a decent mpg....

 

as far as the hopes for a mid teen mpg, im averaging 10 mpg with a 15 to 20k load in tow so is a 3 to 5 mpg increase with a more highway friendly gear ratio and programmer unreasonable to expect?

 

@ phy.. tell me more about an OD unit, ive got a zf5 under it now, is there some way to add a OD to it or are you saying get a different tranny?

 

You can put a Gear Vendors OD after the trans...
They're pricey, but they come up used occationally...
Gear Vendors under/overdrive, Application Guide Manual Transmissions.