Help on speedometer spline

[AaronW]

Hi all:

My son's 1975 GMC K15 needs some speedometer help. It's got a right angled gear that comes off the transmission, that's driven by the gear that comes out of the trans. These two gears appear to have been connected with some sort of spline, which was broken. The cable side of the equation, that threads on to the other side of te right angled gear is fine (or looks that way at present). We had to drill what was left of the spline out of the end of the transmission gear, as it was wedged in there pretty good. You can feel that there's a little flat inside there, so I'm assuming we're on the right track, that that that's how these two gears were joined together. Set me straight, if I'm wrong.

So...I've been looking around for a replacement, but I'm not sure what it's called, and I haven't seen anything that looks like what we need.

What do you know?

Aaron

 

[xm20k]

Unless they need the cable to clear something, the cable should just thread onto the housing at the transmission.

 

[PrairieDrifter]

Unless they need the cable to clear something, the cable should just thread onto the housing at the transmission.

There are gear reduction adapter boxes sometimes

 

[xm20k]

There are gear reduction adapter boxes sometimes

Could be.

Look at the gears if they are the same tooth count just cut at a 45, toss it and connect the cable directly to the trans.
If they are 2 different tooth counts, it's a gear ratio adaptor. reduction or increase depends on which is the smaller gear vs which is larger.

 

[AaronW]

There are gear reduction adapter boxes sometimes

Yes, it has a gear reduction box. So its the connector spline between that box, and the gear coming out of the trans housing.

Aaron

 

[xm20k]

Rather than fool with an adaptor I'd just put the correct gears in it.

What trans, gear ratio, and tire size?

 

[Turbo4whl]

Rather than fool with an adaptor I'd just put the correct gears in it.

Automatic transmissions have a wide assortment of speedo drive and driven gears. Manual trans and some transfer cases do not. Many squares came with a ratio adapter.

@AaronW The drive in the ratio adapter will break if the adapter locks up or the speedo cable fails. Can you spin the adapter? If the adapter is okay, I would just make a new drive spline. File or grind a nail square, glue the other end in the adapter. You already drilled the hole in it.

 

[xm20k]

From a little research these are keyed not just a square piece bridging the gap from adaptor to trans try looking at the drop menu here and see if any of these looks correct.

Speedometer Ratio Adapter Keys | 12 Sizes | Automotive, Industrial & Metric0.104 Square - HR176 - Automotive

Precision steel ratio adapter key tips in 12 sizes for automotive, oil & gas, industrial & metric applications. Compatible with ratio, dual drive & right angle adapters.

mrspeedometer.com

 

[AaronW]

Rather than fool with an adaptor I'd just put the correct gears in it.

What trans, gear ratio, and tire size?

4 speed manual. Don't know about the gearing. It's got 17" tires. You'd have to replace the whole cable and sheath, too, since it won't make the 90 degree turn to the transmission, as it is.

 

[AaronW]

Automatic transmissions have a wide assortment of speedo drive and driven gears. Manual trans and some transfer cases do not. Many squares came with a ratio adapter.

@AaronW The drive in the ratio adapter will break if the adapter locks up or the speedo cable fails. Can you spin the adapter? If the adapter is okay, I would just make a new drive spline. File or grind a nail square, glue the other end in the adapter. You already drilled the hole in it.

I hadn't thought about using a nail, that's a good idea, would be pretty simply to modify.

 

[AaronW]

From a little research these are keyed not just a square piece bridging the gap from adaptor to trans try looking at the drop menu here and see if any of these looks correct.

Speedometer Ratio Adapter Keys | 12 Sizes | Automotive, Industrial & Metric0.104 Square - HR176 - Automotive

Precision steel ratio adapter key tips in 12 sizes for automotive, oil & gas, industrial & metric applications. Compatible with ratio, dual drive & right angle adapters.

mrspeedometer.com

I'm pretty sure that's it. Thanks for the link; I hadn't run across that website. Since I haven't got the original part. I'll have to see if I can get an accurate measurement on the hole the key fits in.