NP208 transfer case factory Drive Gear ID

[Sharecropper]

The speedometer is controlled by a "Drive Gear" inside the NP208 transfer case and a "Driven Gear" mounted inside a removable sleeve on the side of the transfer case, to which the speedometer cable is attached. GM offered (and still offers) various teeth counts on both "Drive Gears" and Driven Gears" so that the speedometer is correct to the ground speed, based on different combinations of "Drive" and "Driven" gears.

Does anybody know which speedometer "Drive Gear" GM installed in the CUCV NP208's? The "Driven Gear" is easily changed from outside the case, however the "Drive Gear " can only be changed with the transfer case disassembled. If we knew exactly which "Drive Gear" was used originally, we can then easily determine which "Driven Gear" to use to correct the speedometer based on tire size. It will only be Blue, Red, or Gray. Only someone familiar with the NP208's internals would know this. If this can be determined, I will invest the time to develop a chart for correct speedometer readings based on tire sizes.

As a follow-up, the Blue "Drive Gear" is 18-teeth, the Red "Drive Gear" is 17-teeth, and the Gray "Drive Gear" is 15-teeth.

Here are a couple photos of how the "drive" and "Driven" gears go together. The first photo is a cutaway image showing how they mesh together in the transfer case. The second photo shows what they look like laying on a table.

 

[cucvrus]

Do you need a new gear for the cable adapter and the tail shaft? I think I have them in GM boxes somewhere here.

 

[Sharecropper]

Rick - no, I'm just trying to develop an easy chart for all SS members to use so they can correct their speedometers based on tire size. The Driven Gears are readily available on Ebay. There are a total of twelve (12) of them, ranging in teeth count from 34 to 45.

 

[Sharecropper]

OK, based on Item #12, Figure 83 in the 34P TM, the Drive Gear is a GM part #14037997 which is a gray 15-tooth Drive Gear.

So here is the formula to determine the correct Driven Gear based on axle ratio and tire size:

# of Drive Gear teeth X axle ratio X (20168 divided by tire diameter) divided by 1001 = # of Driven Gear teeth

This can be further studied at http://www.73-87.com/7387garage/drivetrain/speedo.htm

The article is for a 700R4 transmission however there is no difference in other transmissions.

Hope this helps.

 

[Recovry4x4]

I have one somewhere from my grenaded transfer case. Memory says it was gray. I'll try to find it an confirm.

 

[Sharecropper]

Ok I have worked it out for everyone running 37's with 4.56 axle ratio. To correct the speedometer, you will need the 38-tooth Blue Driven Gear, GM Part #1359272, along with the #25512340 sleeve.

Hope this helps.

 

[Sharecropper]

Ok I have worked it out for everyone running 37's with 4.56 axle ratio. To correct the speedometer, you will need the 38-tooth Blue Driven Gear, GM Part #1359272, along with the #25512340 sleeve.

Hope this helps.

CORRECTION - I made one small error in calculation, so the correct Driven Gear will be the 37-tooth Red gear, GM part #1359271. Still used with the #25512340 sleeve. Sorry for my error.