I got a 1999 E350 with the v10 and auto trans. My rear end gears are on their last legs and the BOM says I have 3.55 gears. Since I'm going to be in the market for new gears soon I was wondering if I should stay with the 3.55 or get the 3.73 or 4.10 that were also available for that truck. I get 10mpg so it can't possibly get any worse. Any help is welcome.

 

Really depends on what you use your van for. I recently dropped $500 changing from 3.73 to 4.30's to help my towing capability and am disappointed. I got the entire rear end from a boneyard for $350, I would consider that before you have the gearset changed.

 

If that 10MPG is towing heavy, or in stop-and-go traffic, lower gears will help your mileage.

Remember, in an E-series that the road speed is not pulled from the rear end like the F-series, so any gear changes are either going to need a recalibration at a Ford dealer, or a speedo-gear swap. Not sure what the '99 E-series used. I think they used output shaft speed at the tranny.