Stock 1998 Expy pulls my 2500 lb boat/trailer well, but really struggles with a 4500 cargo trailer. RPMs are about 2300 out of overdrive and climbing hills is a real challange and I get 9 miles to the gallon. Acceleration is better at 70 mph than at 60 because of the low revs. Would like to go to a 3.73 to get higher up the torque curve.
Question: Should I have someone change my ring and pinion or go the the salvage yard and a complete pumpkin with 3.73's and put that in myself. Pulling axles and the differential swap is easier than changing gears, at least for me.
Anybody have an idea how much the dealer would change to change ratios?

 

Welcome ! Your truck doesn't have a drop-out pumpkin. The pinion assembly and differential assembly is installed directly into the housing. You'll be fine having the gears changed out in your original rear end. Expect $600+ per axle.

 

The Ford 9" uses a drop out center section and that axle hasn't been used since the early/mid 80s. In order to change gears will require a complete setup which includes shimming it to set the pattern and backlash. I agree with Max that if you thought that the 9.75 or 8.8 used a drop out center section then you're better off going to a shop as this is not just slapping in gears. There is alot of precision in this to keep the gears from chewing themselves up and keeping them quiet. Also remember that if this truck is a 4x4 you will need to gear the front axle as well. I wouldn't go much deeper than 4.10s with stock tires or else your empty mileage will decrease and you will lose any gain you'd get from towing. Bottom line, gears will give you 1-2 mpg better towing MAYBE. Its going to take alot of towing to make up the cost of the gear swap. I'd just leave it be since those mpg aren't that much out of line. You've got an Expedition thats not all that light with a small V8 gas engine. Don't expect it to pull like a diesel.

 

Thanks for the info guys. I had vans for years, mid 80's, and got used to the removeable pumpkin, I just "assumed" the 2wd Expy I have now is also, to lazy to actually look underneath. I'll struggle with the current setup, thanks again.

 

I don't know much tread you've got left but, you can achieve the effect of a gear ratio change by choosing a tire that is not as tall as your current one.