Hi,

I recently bought a 1991 F250 with a 7.3 diesel (manual transmission) thinking that it could safely tow around 10,000 lbs. Apparantly I was wrong. According to Ford, the recommend GCVW rating for my vehicle is a mere 12000 lbs. This isn't enought to tow a boat I was looking at it which weighs 6600 lbs (8000 to 9000 with the trailer). So I talked to the local Ford dealer about modifications that would substantially increase the towing capacity. In particular, changing the rear axel ratio from a 355 (which was originally installed on the truck) to a 373 or 410. The service guy at the dealership assured me that this single change was probably enough to bring the max towing capacity of my truck to the 10,000 + lbs that I need. This seems like a huge difference for such a small change. Does this sound correct? Are there other limitations of the truck that I should worry about? Would a modification like this be enough to assure my insurance company that I am towing safely? How would the change in axel ratio effect performance, shifting, fuel efficiency? Any thoughts?


thanks!

Sam

 

You have to take into effect brakes, cooling, tranny cooling and Springs

Brakes you may need to go larger or a better brake pad

cooling, You should be ok there, but keep an eye on it you may have to get a larger radiator

tranny cooling, add a aftermarket cooler and you should be good

springs, they should be heavy enough but if it sags, look into either a helper spring or airbags.

Axle ratio I'd go to 3.73 if this is a daily driver, you'll suffer a little towing but save a bit in gas

if mileage isn't a concern go to the 4.10 you'll be glad you did everytime you tow.

 

is cooling also an issue with manual transmission, or is it strictly an automatic transmission concern?

 

From the 1991 Ford towing guide:

F250 manual transmission--4x2--
3.55 gears 12000 gcvw 6900 max tow
4.10 gears 14000 gcvw 8900 max tow

Only automatic transmissions go over 10000lbs tow capacity in 1991

 

thanks for this info!

It seems to contradict what the dealer told me. He said the 410 axels would put me over 10000 towing capacity. I have heard from others that Ford did not rate manual transmissions very high because they didn't trust owner's would drive them correctly with heavy loads (thus wearing out the clutch and transmission I suppose?).

It sounds like I should have gotten and automatic. Bummer!

Sam

 

You should be fine even with the 3.55. As far as I know they did not change sprigns or brakes for lighter towing capacity. You will not be able to accelerate as fast with the higher gearing but should just fine.

 

Only automatics need aux tranny coolers. Automatic transmissions usually get hot because they "search" gears, overheating the transmission. There isn't a huge difference between the 3:55 and the 3:73, I wouldn't change it. If you want torque and don't care about fuel economy, the 4:10 would work better.

 

It sounds like the gear swap would do the trick. I wouldn't worry about the tranny. That's a heeeeavy boat!

 

sorry did not notice you put in manual trans.