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I am starting into the restoration of my 1970 D100. This truck has the 4 speed manual transmission and a 225" slant six engine. The truck moves along pretty well, but it has pretty low "farmer" gears in the diff; I'm not sure what the gear ratio is but will look for a tag once I get the rear end out of the truck.
My question is, how easy and expensive is it to change out the gear ratio in the rear end of one of these trucks? Is there a supplier out there of rear end gears?

Changing out the original "3rd" member" or center section gear carrier in an 8-3/4 rear end is simple. Then you can simply reinstall everything with a 3rd member from another car or truck with the ratio you want. Buying a gear set (ring and pinion) and then replacing your existing gears is also able to be done but is a little more involved for someone who doesn't have the tools and experience to complete the job. Changing the gears is not difficult but setting them up correctly takes some time and the correct tools.

- EM

The ratio is printed on the vin tag.

Cool; I'll check it out tonight.

Probably the 3.91 Farmer ratio.

John

Finally got around to looking at my vin tag; I have the 3.55 to 1 gears with heavy duty rear springs.
Does anyone have an opinion if this is a decent all around ratio? Havent driven the truck much before I tore it apart for a restoration.
If it would be improved by changing the gears, what ratio would you guys recommend for all around driving with quite a bit of highway driving mixed in?

fireguyfire wrote:Finally got around to looking at my vin tag; I have the 3.55 to 1 gears with heavy duty rear springs.
Does anyone have an opinion if this is a decent all around ratio?

As far as passenger cars & 1/2 ton trucks, if there was ONLY one ratio available then I suspect this would be the best. I had 3.55 in my RR & GTX's, loved it.

With your 435 & the torque of the /6, acceleration shouldn't be an issue unless your tires are extremely tall/wide/heavy.
Hwy cruising however would benefit from taller tires.

Bucky

Thanks Bucky!

The 3.55 is a nice gear as Bucky pointed out. The 3.23 is pretty decent too
if you weren't planning on doing a lot of heavy hauling or towing.
John