Changing Differential Ratio

[Trainmaster]

The 3rd generation Expeditions came with two different rear end ratios. Can anyone tell me what's involved if I wished to change from one to the other? Thanks much.

 

[Trainmaster]

Now that I'm thinking about it, a 4X4 would need both the front and rear differential ring gears an pinions changed, along with the crush sleeves and pinion nuts. I think I just answered my own question... It's way too much work!

 

[ExplorerTom]

It’s not unheard of though. My Explorer came with 3.55 gears but now has 4.56 gears. My Expedition also has 3.55 and have been considering 4.10.

 

[powerboatr]

not hard, but it was three ratios
should be easy parts wise then have all the backlash set up

 

[1955moose]

If your talented, and can figure out how to do the proper torques, and crush sleeves, and all that hoo ha, go for it. Are you trying to go go lower, or higher in gearing? Most want lower, 331 vs 373. If your going higher, say from too low gearing to higher, taller tires will cure that. The other way around you can do to a point. A lower profile tire will lower gearing, but also the load your vehicle will carry. Easiest bet is find both differentials complete with everything, and just bolt in.

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[Trainmaster]

I wanted a higher ratio. Drove the SSV's for years and they had better get up and go because of the rears. But I don't want it bad enough to do the work...

 

[JExpedition07]

Did the SSV use a 3.31? The 5.4 3V/ 3.73 with the 6R75 is a great combo I don’t think the 3.31 is as good of a ratio for this setup. Especially in a heavy truck based SUV, if anything I think you’d lose get up and go with higher. Mine performs well with the 3.73 rear.

 

[LRNAD90]

I wanted a higher ratio. Drove the SSV's for years and they had better get up and go because of the rears. But I don't want it bad enough to do the work...

Unless I am misreading things, I think you've got that backwards. Lower gears (numerically higher) will give you better acceleration, higher gears (numerically lower) will hurt acceleration.

 

[chuck s]

A lower gear has a higher number. It's actually a ratio which is a reciprocal. 1/3.73 = 0.238 vs 1/3.31 = 0.302. When you do the actual math the 3.73 is lower.

My '07 5.4 V8 had the 3.73 axles, my '17 has 3.31. The '17 has much better performance (AKA acceleration) due, no doubt to the 3.4 EcoBoost engine. All this is by feel, I lost the timing slips from the local drag strip.

-- Chuck

 

[1955moose]

I'm guessing he means higher numerical, lower gears. It is a lot of work swapping out front and rear. Not to mention double the costs. Like my older brother said to me years back when I commented I wanted to put a sunroof on my Datsun 240. His words were, save your money, and buy a newer car with one already installed! Smarter words were never more true. Leave it be, later buy a newer Suv/pickup, that has what you want already.

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[Trainmaster]

I'm with you, Moose, as usual. Old skool guys think alike. The SSV's has 3.73, which I liked a lot. The 3.3 tends to drag ass a bit from the line, and doesn't have the kick on open throttle acceleration. But I'll learn to live with it and save the money and blood for fixing all those things that are just waiting to break.

 

[ExplorerTom]

Instead of opening up the diffs to swap ratios, since you thought about going to an existing ratio, just swap the diffs themselves. That would be a purely bolt in solution that any knuckle dragging shade tree mechanic should be able to do.

But after seeing how the 4.56 gears woke up my Explorer, I’d go lower than what factory offers for the Expedition: 4.10 at a minimum.

 

[LRNAD90]

http://www.adventuredriven.com/single-post/2017/09/21/Air-Lockers-and-456-Nitro-Gear-install-video

 

[Trainmaster]

Thanks for passing along that video. Appreciated.

 

[1955moose]

I remember back in the late 60's, my first motorcycle was a small twin cylinder street model Yamaha. Bought it for $135.00, a lot of Dinero for me at the time. I mounted knobby tires, and I replaced the little 34 tooth rear sprocket, with a 57 tooth monster. Man did that little 100 cc bike turn into an animal. I lived right against the San Bruno mountains here in Daly City. After that transformation, that little bike climbed like a Billy Goat. Problem was after the gearing change, it tached out at 42 mph! The bike was only 13 hp, so couldn't cruise the freeway legally anyway. Funny how you never forget your first girl, or car/motorcycle.

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[Plati]

the Adventure Driven website is great, thanks!

TFF ... my second motorsickle was that same YL1. First was a Honda 50. I also put a knobby on the twin 100cc and a bigger rear sprocket (and many other things). I completely ripped it apart one winter and replaced the entire wiring harness (12 years old). Turned my yard into a motocross track and used to run loops around the house with the muffler completely removed. Quiet residential neighborhood. I kept crashing and ripping the brake lever off so I just went without brakes and downshifted to stop. It had a battery & one day I crashed and the battery fell out. The thing kept working because it had a magneto so I just left the battery on the ground didnt replace it. I remeber buying gas with pennies, a nickel, a dime if I was lucky (from returned bottles) at $.28/gal

Back in those days most kids were riding mini bikes so I was the King!

 

[Trainmaster]

Rather remember my first girl. My first car was crap...

 

[1955moose]

That's the bike! Mine was the same color. I too installed a racing magneto, but later returned it back to battery/ charging system. Those little 100 twins were bullet proof. Ford should have taken cues from Yamaha. Hey wait a minute, didn't the Sho Taurus use a Yamaha engine? Maybe Fords smarter than they appear to be. Harley Davidson big twins had horrible brakes/suspension, till finally they outsourced Japanese Forks, and Italian brembo brakes. With all our brilliant minds in this country, amazing how we've got to keep tapping the Japanese, and Germans, and Italians for fixes. The same people we fought to defeat 73 years ago. Kinda like your best friend was a guy you hated, and fought with, when you met.

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