Speedometer question

[McC_65_91]

so i disconnected my non-working speedo cable the other day to try and narrow down the problem. disconnected from the transfer case (4X4) and the gauge, spun it and all good, kinda disappointing tho, already got a cable with my last big order, figured it was like $15 so might as well just order it, but now dont need it.

next i reconnected the cable to the T-case and started driving with it disconnected from gauge - cable not spinning... this would lead me to assume that it is the sending unit on the T-case right??

has anyone else done this on a 4x4? or know if the T-case sending unit on a 4x4 is the same sending unit on tranny on a 2wd?

all thoughts advice and help appreciated
PS its a 65 GMC, 4 speed

[raycow]

The cable is driven by a pair of gears in the transfer case. You can unscrew the fitting or sleeve that holds the driven gear and take a look at it. Once that is out, you can shine a light into the hole and look at the drive gear. The driven gear looks similar to the one used in the older 2WD 4 speeds, but I can't swear that it's identical.

Ray

[McC_65_91]

alright well ill take a look this coming weekend (im in college about an hour away) this sounds about right and the way i diagnosed the problem it seems like this has to be the problem.
Does anyone know where to get this part? or even one for a 2wd? im guessing it would be called a speedometer sending unit? or something similar. I looked in car and truck shop catalogue and LMC and didnt see anything like it. But it may also be a part i could get from any parts store if I know the gear ratio right?
any more advice in obtaining this part and help?
thanks

[raycow]

These are not parts store items. Speedometer and transmission shops have them sometimes. However, you don't really want to go buying parts before you look at the old ones and find out exactly what the problem is. You can always drive the truck just by screwing the driven gear fitting back into the transfer case so oil doesn't leak out of the hole.

Ray

[aerotruk63]

[aerotruk63]

Gm parts book says
GEAR UNIT/ SPEEDOMETER DRIVEN
1...2396889..... 63-66 ALL W/4 SPD TRANS...11 Teeth
1...2396888..... 63-66 K20 w/4 SPD TRANS... 12 teeth
1...2396890..... 63-66 K20 W/4 SPD TRANS... 13 teeth

None of these numbers match any of the 2WD numbers. W/4 SPD TRANS

[raycow]

Originally Posted by aerotruk63

None of these numbers match any of the 2WD numbers. W/4 SPD TRANS

Aerotruk, you are absolutely right. The gear in the diagram doesn't look anything at all like I was expecting. I must have been thinking of the wrong model transfer case. My thanks to you and my apologies to McC_65_91.

Ray

[aerotruk63]

raycow So which gear do you think is broken because part 28 and 38 are listed as speedometer gear?

[raycow]

With my luck, it would be 28 because it is more difficult to replace. However, either one or both can go, so you can't really know until you get a look at the parts. That's why I suggested unscrewing the sleeve and shining a light inside before trying to order anything.

Ray

[padresag]

if you unscrew the sleeve then the driven is on that, but you will be better to replace both. it is not a major job, drop the shaft ,trans yoke and the short ext hsg and your there
ron