Transfer case with .85:1

[desertprep]

Has anyone seen a transfer case for the 'stro with a .85:1 high gear? I would like to put 4.11's in the rear ends and the .85 gear would give me better highway mpg.

[MountainManJoe]

Hi, welcome to the forum.
You mean like an overdrive unit? I've never seen anybody put one on a 'stro. Most people just run the 4.11s as is.
But anything can be done with enough ingenuity.

[desertprep]

Thanks! an overdrive unit would be one considering. I was thinking about changing the gear ratio of a transfer case from 1:1 to .85:1 That way high gear is still about 3.5 to one but low gear, with 4.11's would still be nice and low.

[MountainManJoe]

I've never heard of a transfer cases that increases RPM. Did you find one?

Is your 'stro RWD or AWD ?

[desertprep]

AWD

[MountainManJoe]

AWD. So that means a few things. You can't just change your rear gears. You have to do both front and rear. If you're paying someone to do it, then you're easily looking at the same kind money than the van is worth.

Whenever 4x4 transfer cases have additional ranges, it is typically low range for challenging terrain. Like I said, I think you'll have a hard time finding a transfer case like you're talking about, if it exists at all. I've heard of overdrive units, but it will take fabrication at some expense to adapt it to your Astro. You will need adapter plates, mounting system, some kind of drive coupling, and of course shortening of your existing driveshaft. Big project. Lots of engineering and fabrication.

I was thinking about changing the gear ratio of a transfer case from 1:1 to .85:1

So a custom transfer case? It's not like doing a rear end. Transfer cases weren't designed to be modified like axles. It would probably be less effort to design one from scratch.

Putting in a final drive with more reduction, at the same time as gear multiplication is counterproductive. It defeats the purpose. Choose either more torque, or better fuel economy. One or the other. Trying to have it all would involve more money that you will ever gain back with that extra fractional MPG.


To be perfectly honest your idea doesn't make much practical sense. I think you're barking up the wrong tree and wasting your time.

[photo_van]

If you are going to 4.11 we might assume you are also going with larger tires? Match the tire size to the gear size and there is no change in RPM/MPH. At that point any loss in MPG will be due to the required increase in power to move the additional weight/resistance of the larger tire. As for changing gears in an NVP TC: the 1:1 is achieved by a direct coupling of the input and output shafts, there are no gears involved in 2hi.

[Bret Schmerker]

The lightest transfer cases to my knowledge that have overdrive are built into the crawlerboxes on Class-5-and-up Macks. Even StaK 4x4 transfer cases don't have overdrive among the gear options; neither does Advance Adapters.