M1009 Speedometer Cable Replacement?

[HelluvaEngineer]

Does anyone have any recommendations for part numbers for replacing the speedometer cable and the gear on the transfer case? I am running 33's with stock differential gears.
Edit: this is an M1009.

 

[royalflush55]

What are you working on???

 

[HelluvaEngineer]

What are you working on???

I rebuilt some stuff in the gauge cluster, including a new speedo. I lubricated the cable, reconnected it, then took a test drive. The needle was bouncing then stopped completely. When I inspected the cable, it was knotted up at the xfer case side, and it was really difficult to remove. I'd like to replace the cable assembly and put a new gear in the xfer case while I'm there.

 

[Sharecropper]

I am confident that a new AC Delco speedometer cable can be easily sourced on Ebay - simply type in the GM part number: 25033627. Regarding the driven gear and sleeve at the transfer case, you may find this post helpful: https://www.steelsoldiers.com/threads/calibrating-speedometer.223246/

 

[Barrman]

I think the what are you working on question was referring to the CUCV model. They all had the same set of gears inside the tail shaft. But, the M1009 trucks got a fancy little reduction box to go between the tail shaft and the speedometer cable because of the different axle ratio they have. You didn’t mention that so my guess is you are not working on a M1009.

Unfortunately I only have experience with a M1009 set up. Adding 33 x 12.5 tires to a M1009 makes the speedometer and odometer 10% slow. The federal standard as I understand it is an allowable error of 3-5%. Each step of the gear changes in the speedometer drive system is also 3-5%. Which means 1 step gets you technically legal and 2 steps gets you theoretically right on.

But, do you have the stock drive and driven gears in your transfer case and how accurate is your speedometer? I would suggest you get the new cable assembly and drive the truck. Use GPS or interstate mile markers and a stop watch to figure out how far off you are. Also figure out what color gears you have inside while doing the cable install. If your plastic drive gear that the cable slips into looks or feels rounded. I have had good success with wrapping the cable with a small bit of aluminum foil to make it a non slip tight fit.

 

[Sharecropper]

I think the what are you working on question was referring to the CUCV model. They all had the same set of gears inside the tail shaft. But, the M1009 trucks got a fancy little reduction box to go between the tail shaft and the speedometer cable because of the different axle ratio they have. You didn’t mention that so my guess is you are not working on a M1009.

Unfortunately I only have experience with a M1009 set up. Adding 33 x 12.5 tires to a M1009 makes the speedometer and odometer 10% slow. The federal standard as I understand it is an allowable error of 3-5%. Each step of the gear changes in the speedometer drive system is also 3-5%. Which means 1 step gets you technically legal and 2 steps gets you theoretically right on.

But, do you have the stock drive and driven gears in your transfer case and how accurate is your speedometer? I would suggest you get the new cable assembly and drive the truck. Use GPS or interstate mile markers and a stop watch to figure out how far off you are. Also figure out what color gears you have inside while doing the cable install. If your plastic drive gear that the cable slips into looks or feels rounded. I have had good success with wrapping the cable with a small bit of aluminum foil to make it a non slip tight fit.

Ditto what Barrman said. The OEM driven gear GM installed in the CUCV NP208 transfer cases was the 41-tooth yellow gear, GM part #1362195. To speed-up the speedometer reading when driving, the tooth count of the driven gear should be reduced; similarly, to slow the speedometer reading when driving, the tooth count of the driven gear should be increased. Each tooth on the driven gear added or subtracted will result in approximately 2 MPH reading on the speedometer. But take note - if you need to speed-up the speedometer reading, you will also need to use a different sleeve for the driven gear. The OEM CUCV sleeve is a GM1362077, which is for driven gears of 40 to 45 teeth only; if you need to reduce the tooth count lower than 40, you will also need to use a GM1362076 sleeve which will accommodate driven gears with tooth counts of 36 to 39. All of these GM part numbers are readily available on Ebay.

To determine the exact required driven-gear tooth count of your specific application, do the math as explained in the link in my thread above. It works and will get you within 1 MPH of absolute accuracy at 60 MPH.

 

[HelluvaEngineer]

Apologies.
It's an M1009 and it does have a reduction box on the side of the xfer case. I missed the intent of the original reply.
Just assumed I had mentioned M1009.

 

[HelluvaEngineer]

See above. There is some kind of horrific graphite lubricant gunk in the reduction box that is likely 40 years old. I'm considering pulling off that unit, disassembling it, and throwing it in my ultrasonic cleaner. At this point I'm not focused on an accurate speedo, but my questions now are:

1. What is the correct lubricating procedure for the reducer?
2. Are different gears even available if I decide to go that route?

Thanks for all of the replies and apologies for not mentioning the vehicle upfront.

 

[HelluvaEngineer]

It looks like the updated PN may be 88959481. Still trying to confirm.

 

[HelluvaEngineer]

Referencing https://www.steelsoldiers.com/threads/speedometer-adapter-assy-6-m1009.70087/

I've been bouncing this off of ChatGPT trying to get the current part numbers, most of which are wrong. What I find interesting is that it made the recommendation of just removing the adapter box and getting the correct gear. It is suggesting a 40 took gear, but I have not confirmed. Given the mentions of that adapter failing, this seems like a good idea. Does anyone have experience with this? Part of the CGPT convo:



Your M1009 (like all CUCV trucks) has a VSS (Vehicle Speed Sensor) ratio adapter box mounted between the transfer case and the speedometer cable.
This metal box is what you're calling the reduction box — and yes, it absolutely affects the calculation. Let’s break this down:


What is that box?

It’s a ratio adapter — essentially a small gearbox that spins the cable faster or slower to correct for axle ratio and tire size from the factory.

• On the M1009, this adapter corrects for:
  • 3.08 gears
  • ~31.7" stock tires

The ratio is usually stamped on the box itself — something like DRIVE 16 / DRIVEN 21 (or similar), which equals 0.76:1 reduction
(The output spins slower than input)


Does it still work with 33” tires?

Well…
Since your tire diameter increased, the original ratio adapter will now be over-correcting, making your speedometer read even slower than it should.

Example:
Larger tires = speedo already reads slow
Ratio box slowing it further = speedo reads even more inaccurate

So what should you do?

You have 2 options:

Option	What you do	Result
1. Remove ratio box	Delete the adapter and run cable straight to transfer case	Simplest fix, less clutter, recalibrate with correct gear
2. Keep box, recalibrate driven gear	Leave box, but calculate new driven gear to counteract box ratio	More complicated, keeps VSS signal if you care about it

Most guys on SteelSoldiers just delete the box (since it's not connected to anything critical on an '84 M1009).
The VSS was for cruise control and diagnostic purposes, which you likely don't use.


How to delete the ratio box cleanly

• Remove box
• Connect speedo cable direct to transfer case adapter
  — You may need a female-female speedo cable coupler (or a longer cable) depending on routing

If you delete the box, my earlier suggestion of the 40T driven gear (TCI 88002 is spot on

Summary

• Yes, your ratio box affects things — it overcorrects now with 33s
• Best move? Delete box + install correct driven gear (40T Green)
• Result: Cleaner, simpler setup, speedometer very close to correct