Speedometer drive gear?

[shotty]

Can anyone confirm the number of teeth in the np208 drive gear for a 1008? I'm pretty sure it's 15 and it's the same for a 1008 and 1009 but I want to make sure.

Edit: did some more math, pretty certain its a 15 tooth drive gear. I pulled a 44 tooth driven gear out. Looks like the math checks out nicely for going with larger tires as well:

44 tooth for 31's
43 tooth for 32's
42 tooth for 33's

 

[Sharecropper]

The OEM drive gear in the NP208 is a grey 15-tooth, GM #14037997. The OEM driven gear in M1008 and M1028 is a yellow 41-tooth. No doubt thus combination was for the stock tires and wheels. Not sure about M1009.
Regarding the Drive Gear, fewer teeth will slow down the speedometer reading and more teeth will speed it up. Regarding the Driven Gear, the opposite is true - fewer teeth will speed up the speedometer reading and more teeth will slow it down.
I have a chart somewhere in my computer and tomorrow I will see if I can find it and post it.

 

[Sharecropper]

Can anyone confirm the number of teeth in the np208 drive gear for a 1008? I'm pretty sure it's 15 and it's the same for a 1008 and 1009 but I want to make sure.

Edit: did some more math, pretty certain its a 15 tooth drive gear. I pulled a 44 tooth driven gear out. Looks like the math checks out nicely for going with larger tires as well:

44 tooth for 31's
43 tooth for 32's
42 tooth for 33's

Here is the most helpful site I have found. You can calculate your exact driven gear (if you know your drive gear) based on axle ratio and tire diameter. Or scroll down to see the different gears and their corresponding color and tooth count. Note - in our 4WD trucks the gears are in the tail housings of the transfer case, not in the transmissions.

Note that there are two (2) different driven gear housings based on the tooth count. The GM #1362076 is for 36-39 tooth gears and #1362077 is for 40-45 tooth gears. I may have a few housings and driven gears in my spare parts bin if you need one.

Hope this helps.

TCI Auto Speedometer Gear Calculator - TCI® Auto

Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!

www.tciauto.com

 

[Sharecropper]

Here is another site which shows the GM part numbers of the gears and housings.

Speedo Gears

www.73-87.com

 

[Sharecropper]

If you are not sure about which drive gear you have, simply remove the driven gear and housing and look in the hole with a flashlight. The color of the drive gear will indicate which one you have. Might have to squeeze your head in close, but it works. Or if you have one of those snake cameras, it works even better. I believe the gray 15-tooth drive gear was installed in all CUCVs.

Hope this helps.

 

[shotty]

It does, thank you. I have the 15 tooth, I remember the color and the math checks out for my speedo readings. Looks like someone swapped a 44 tooth driven gear in, and I ordered a 43 but its still a bit off, so going for a 42 now and that should nail it. Speedometer rebuild locally is about $300 so I'm considering that too, but only if the color of the needle isnt too far off my NOS 4k tach I'm installing, otherwise I'll just wait for a NOS speedo to show up so everything matches.

 

[Sharecropper]

I have 2 of those 4000 rpm tachs. One is NOS still in the DELCO box and the other is in a gauge cluster. Your will need a signal conversion box to make it work. I have that too.

 

[shotty]

I have 2 of those 4000 rpm tachs. One is NOS still in the DELCO box and the other is in a gauge cluster. Your will need a signal conversion box to make it work. I have that too.

Already got both Mine is in the delco box as well, pricey but gorgeous and perfect for these trucks. I spoke with the ebay guy that makes the converters and they are coming out with a new one that will work with the 6.5 engine speed sensor. Looking forward to using that in the future but for now the alternator is fine. I even removed the alternator wire from the engine harness on the drivers side and re-routed it over to the passenger side after the 12v conversion.