Originally written by nobodyimportant on 2010-03-09 2:44 PM

The easiest way is to call your local Ford dealer and talk with the service manager.  Give him your VIN and he should be able to pull up the specs.  I would assume that all the 7.3's will have the same axel ratio.  It most likely is the 3.73.  More knowledgeable people than I on this site might be able to tell you with more certainty.

If it is a single rear wheel then it is likely a 3-73.  Dual rear wheel will likely be a 4-11 Although it could have been ordered with 3-73's.  It would simpler to reference the VIN.

If it's the Single Rear Wheels.  It WILL be the 3:73 unless somebody changed it after it left the factory.

The only option Ford offered on the diesel Single Rear Wheel configuration was the Limited Slip vs the Non- Limited slip.

You could get the other axle rations in the Duallys, But not the Single.

Gard,

I think for pulling, my '99 Ford PSD would be better with the 4:10's.

Here's why. It has a sweet spot of about 2000 rpms. That is over 70 mph. The thing is if you tow around 65 mph (maybe 1600 rpm), just about any hill will drag you down causing it to downshift.

The 4:10's would allow for some more rpm...and I think the drivability wold improve....while towing. Empty? Hey, 3:54's would be nice....3:08 even better.

My '96 had 4:10's....not nearly the power of the '99, but I feel was better with the trailer.

Of course...your mileage may vary.

The weight of your trailer and the terrain in which you are traveling, will determine how well your truck handles the load. If you have heavy equipment and many hills, the 4.10 ratio would be an excellent choice.

Our smaller trailer only weighs 5600# empty, the larger 9,600#.

In western PA we have many hills. Before we installed the programmer, the transmission would often kick out of OD, when we ascended any of the steeper ones while towing the larger trailer. Now it's an infrequent event when that happens, even with the setting on the lowest "towing" selection. Now a hill results in the turbo giving a little more boost, the transmission remains in a torque converter lock up, and the cruise maintains the engine and road speeds.

The mods we have made have enhanced, an already competent towing vehicle. It has an adequate power range, absolute reliability, and is comfortable as well. We have no plans to replace it with a new $50k variant.

Dave, 

Thank you, although I have no idea what it means, except for the 3.73 part! 

Thanks, gard, but what is "open differential, 10.5" Sterling type" ?  I am confused!  Also, how will this affect my truck's towing?

An open differential means It is not a limited slip differential. Sterling is a supplier/manufacturer of Ford axle parts. A non limited slip differential will spin one tire that is in poor traction conditions, and not supply torque to the opposing axle even it were on bare concrete.

Gard,

Is this good or bad for towing?  Thank you.

Bad

A non limited slip differential will spin one tire that is in poor traction conditions, and not supply torque to the opposing axle even it were on bare concrete.

Well, hopefully the 4wd will help out if we get stuck.  So far, I've really liked my truck (Ford F350 SD 4x4 7.3L d).  We had the turnover hitch put in last year, a plug added in the side wall of the truck bed, plus had Linex sprayed on the bed.  I hope we can add a gooseneck horse trailer this year.  My husband had some special type of transmission installed, although I have not noticed any improvement on performance.  Maybe that will be realized when we actually pull a loaded gooseneck.  Maybe we'll discover we need an extra leaf or timbrens....who knows?