Under drive idea

[VanBoy]

I've been toying w/ an idea. And I wanted to run it through here to see what people think.... yes it is a costly idea....

Have a 99 PS E350 extended Club Wagon w/ a 3.55 ratio. Most say 3.55 isn't good for much towing (at least heavy and hills) and the tranny will pay it there is heavy towing on hills.

Any how, I was thinking, for the times I need a better ratio then 3.55, would a US Gear UNDERDRIVE work out? According to the chart, 3rd UNDER would be 4.43 ratio. I'm sure that would allow one to pull a good sized hill at 60MPH if they had a 10,000lb trailer.....

Call this a 'theoretical exerciser'.

 

[RLDSL]

You have the right idea. Finding the right gear for the situation will make your engine happy.
I had the opposite problem with 4.10 being too low for most driving, and even when towing 4 would be wound out but 5 would be lugging and require excessive fuel use to pull , but now with the spicer 5831 brownie I installed, 4 over is perfect for most heavy towing. KEeps it up where I'm getting a steady 1.5-2lbs boost and giving it very little throttle and sailing consistantly down the road on less fuel
Being able to split gears gets you where you need to be .

 

[69oiler]

i have the US Gear UD in my '86 CC IDI. there is a difference in pulling power when in low range. i would recommend using the UD if you can get a good deal on one, otherwise i think i'd do a diff gear swap to 3.73 or 4.10 depending on how much towing you do.

 

[VanBoy]

That's what I was thinking..... but being an electronic speedo.... not sure I could find a "used" unit that would match up. It would be the occasional tower.... if ever. As I said, it's a theoretical excersise. A "What IF..." scenario.

 

[69oiler]

FWIW 3.73 makes a good "compromise" gear. i have 3.73s in my SD and i tow with it a lot, like half or more of the miles driven are towing 6000-10000 lbs.

if i'm cruising on the highway in OD i'm running 70 at 2100 rpm or so. if i'm on slower roads i lock out the OD and run in 3rd. 4.10s would be better for when i am loaded really heavy, but the 3.73 is a good setup.

my IDI has 3.55s and so does a friends F350 PSD. we both agree 3.55 is not a good towing ratio for heavy loads unless you are in the flatlands only.