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.

 

How much highway driving do you do ? Going to either of those gears will raise the rpms at any given speed, it would tend to help around town, letting the vehicle accellerate quicker, but could hurt the highway driving with the increased engine rpms.

 

A strong "2nd the motion" of baddad's comment. You should Carefully consider how much time you'll spend at/above 55-60mph.

Even if you ignore fuel economy, consider the wear and tear on running that big V10 at 2,500rpm with all that wind resistance and weight for dozens/hundreds of hours per year. Now imagine the exact same scenario at 2,000rpm. It's a bigger difference than you think.
I borrowed my friends V10 excursion for two weeks and it was just over 2,600rpm at 75mph... For a 30minute drive each way. With 100% "free" fuel (company gas card). It just felt WRONG... Sinful really.

 

This very topic is discussed often in the V10 forums---it might be helpful to your eventual decision reading a bit there too.

Typcially the modular motors seem to like the slightly higher RPM's. Adding a lower rear gear plus a 5 Star turning program you might enjoy your MPH's, MPG's and the RPM's not be such a big change or all that detrimental.

 

I've been accused of "overthinking" many times in life and I suppose this topic could apply as well, but I stand by it.

Go drive your V10 with the overdrive off or maybe shift it to "2" or "3" and go drive around for 5 steady, solid minutes at any speed at 2,600rpm and see what you think.

 

Ditto, go fill it up, the take it on a 50 mile freeway trip with the OD switch turned off, the refill it and check the mileage.

 

Just remember your rear diff isn't the same as the same age truck diff. Your van will have a Dana 60 while the trucks will have a Sterling.

 

I didn't think they put 3.55's behind the V10's.

 

@baddad457. You wouldn't think they would but its the smallest ratio the put in the truck. It's damn fast on the top end but not much off the line through 1st. The shift from 1st to 2nd will put you in the seat

 

My vote is for the 3:73......

 

Same here. 4.10 is too aggressive, unless you're only pulling heavy trailers and stopping a lot that's too low for an all around work truck. The 3.73 will give you a little more grunt on the low end without murdering the freeway driveability... And if the 3.73 turns out too low you can compensate with a slightly taller tire. That wouldn't be in the cards with a 4.10

 

Finally an answer I can use. I figured the 3.73 would be my best bet. I run a 265/75R16 tire and the van calls for a 245/75. Do y'all think I should spring for the L/S or keep the open rearend.

 

If you go off road a lot, then the L/S makes sense, otherwise it's a whole lot of $$$ for very little benefit. I was going to install one in my 99 SD F250 after getting stuck in my back yard for two hours once but after getting aftermarket wheels (16X10) and Gumbo Mudder tires (31570's) on the rear, I've yet to get stuck any more. It formerly had 235/80's all around.

 

What you in effect did here was change the rear gear to a 3.44. Changing the rear gear ratio to 3.73 will be like changing the rear tires back to those 245's. Going to 4.11's will be equal to having the 245's on the rear with a 3.96 gear.

 

Moosey78 you never told us if/how much you will drive highway speeds.