89 K5. NP 241. Speedometer gear problem

[buckallred]

I carefully read what speedometer gearing to get for the 700r4 transmission. Ordered the drive gear, drive gear housing, and driven gear. Then took the thing apart and realized that ... with an NP241 transfer case, it's all totally different.

Now, my understanding is that the speedometer drive gear on the NP241 (which I can confirm mine is light blue in color) has 13 drive teeth.

Assuming that's true, with 37-in tires and 5.38 gears I would need a speedometer driven gear of 38 teeth.

In addition, I bought the wrong speedometer driven gear housing. It was slightly different and didn't fit. Obviously annoying. If anyone can point me to the correct one, so I don't go ordering the wrong thing yet again, I would be most grateful. Yep, it was a bad day taking all that shit apart to realize I had all the wrong parts...

 

[obijuank5]

Yeah that's frustrating for sure. I went to my handy dandy gm parts manual and they just skipped the 89 241 speedometer gears completely.

offroad design helped me last time I needed information about drive and driven gears.

 

[formercruiserhead]

Go to a speedometer shop. I had to show proof I fixed my speedometer to get out of a speeding ticket years ago and they had a ton of different gears and installed the one that was closest for my modifications. They may just sell you one.

 

[ZooMad75]

For the gearing and tire size a speedometer shop might set up a reduction box to put in line of the cable to make the correction for the driven and drive gears you have.

 

[K5Jimmy]

For the gearing and tire size a speedometer shop might set up a reduction box to put in line of the cable to make the correction for the driven and drive gears you have.

I got a reduction gearbox built a Long time ago. The old guy did speedos for law cars pre-digital.

 

[ccj8008]

What year did the NP241 go digital (VSS)? I know my 91 Burbs had it. There was a good thread on this forum to modify the digital speedo board by replacing a few hard wired paths in the circuit board with dip switches. Then you could adjust the output at the board by changing the switch positions. The thread even included the switch position settings for various ratios. It was easy for a first timer to solder in the switches and I modified two boards cause I like spares. I was then able to simply recalibrate my speedo when I went to 4.10 gears, and again when I went to 4.56 gears by changing the switch positions. No gears required.

 

[ZooMad75]

90-91 have electric speedos.

 

[buckallred]

1989 is a mechanical speedp with a veh speed sensor/buffer (green plastic doodad) that I stupidly tossed when I put in an aftermarket dash + speedo. That is ANOTHER problem I have to fix. . .

 

[scouthead]

take speedometer from truck that had manual non overdrive trans, and 3:08 gears and 208 TC...
take axles from truck that had 3:73 gears...
Take mechanical 241 from suburban that had th400 and unknown factory rear axles
combine parts, and run 34-35 inch tires...

PERFECT! verify via GPS -PERFECT readout on speedometer

 

[scouthead]

but since the above might not be repeatable, i also have this adapter box in a pile of parts somewhere... someone above mentioned it.

they used to make adapters that went INLINE - you screw this thing on to your speedo gear housing, and then the speedo cable screws into that... they were avail in a bunch of sizes and ratios? nowadays i cant see there being a lot of speedometer shops in business. I would look on line? order a few and return whatever doesnt fit?