81 Speedo issue
 

My mother has a 81 stepside GMC 350 350 trans.
She was involved in an accident and bent the housing on the rear end. They replaced it with a used one. It had a pretty high road gear that I am not sure of the ratio. They replaced it with a 3.73. The truck still has stock tires that I think are 265/70R/15's. Does anyone know what speedo gears go in it for this set up?

Re: 81 Speedo issue
 

If you go to the dealer, they still have the older books with the speedo gears listed for each tranny/rear end set up. I have most of the numbers copied from their books, but the 350 tranny stuff that I have ends at 3.42 gearing, but they show a #6261782 (9 tooth green color) gear as the drive with a #3987922 (22 tooth gray colored) gear for that combo. These mount with the #6273218 adapter (housing mount piece.) As I said you will have to go to the GM parts counter and ask them to look into the older parts books for the truck/tranny combos. (Speedometer Gear Charts)

When I changed out my rear end to 3.73 gears from the 3.42 gears, all I had to change was the driven gear on the speedo. That was on a 700 R4 tranny.

3.73 gears on a 350 tranny makes for a low geared stump puller, Gas mileage went to heck--

Re: 81 Speedo issue
 

I don't know right off hand, but http://novaresource.org/speedo.htm has a formula that uses gear ratio and tire diameter to help you find an appropriate gear set.

http://tciauto.com/Products/TechInfo/speedo_gears.asp has a tire diameter calculator.

If she'd rather have a highway gear, call me at 424-5170.

Re: 81 Speedo issue
 

Check this out -

http://www.transmissioncenter.net/sp...n_______va.htm