SM465 4 speed manual- removing speedo gear drive

[jdaley]

My 1976 C20 has stripped the speedo drive gear in the gear box. I cannot work out what spanner size is needed to get the 'body' of the drive gear off the gear box. It is something like 1 1/8 inch or 28mm AF, but the engagement edge of the nut is about 3mm.
It may actually be called, 'speedometer drive adaptor nut"
Has anybody had experience with this please?
Thanks in advance.

[wixthedog]

How peculiar that I am in the same boat now! I tested by cables/speedo by running it will a drill and it did well so I narrowed it down to the same issue as you - within the speedo gear of the transmission.

I don't have an answer now but hopefully by end of day I'll have something to contribute.

[mongocanfly]

Are you referring to removing a spanner nut?....a flat face puch will remove it if the nut is what your removing..
This is a 4x4 sm465 but he shows spanner nut removal about 2-1/2 minutes into his video..
https://m.youtube.com/watch?v=0wMUZ-m4f6w

[jdaley]

I am learning more each time I go under the truck.
At the back of the gearbox Chev have installed a rear bearing support I think is its name. The Uni joint is the next bit.
On the Left hand side there is a unit to which the speedo cable screws to.
That part may be called the Speedometer drive adaptor nut.
It screws into the side of the extension piece.
And it has a very narrow hexagon nut about 3mm high. I now believe it is 1 1/16 inch and need a an open ended spanner, because a socket pops off.
I can grind a socket down so it will stay on the nut faces I have been told.

[wixthedog]

Sorry John, picked up a welding job that bit into my fun time. Cash is cash though...

I did take a look at the case and see what you are describing, a really shallow nut that looks like it will be a bear to get off. We may be learning together mate.

[ACS]

This is 2mm thick (5/64”)
https://www.parktool.com/product/28m...-wrench-scw-28

I don’t know about Australia, but I bet a local bicycle store has this or something similar.

[jdaley]

I have found a 11/16 inch open ended spanner, if thats too big I will look at that bicycle spanner. Its 'cold ' here 5deg C, I will wait for temp to increase a bit!!
How you blokes work at minus anything amazes me.

[1976gmc20]

Originally Posted by jdaley

I have found a 11/16 inch open ended spanner, if thats too big I will look at that bicycle spanner. Its 'cold ' here 5deg C, I will wait for temp to increase a bit!!
How you blokes work at minus anything amazes me.

Well, when it's five degrees where you are, it's forty degrees here


Oh, one time I had to put a muffler back on at -54 F. I was a lot younger then, and it was a dry cold.

[geezer#99]

Originally Posted by jdaley

I am learning more each time I go under the truck.
At the back of the gearbox Chev have installed a rear bearing support I think is its name. The Uni joint is the next bit.
On the Left hand side there is a unit to which the speedo cable screws to.
That part may be called the Speedometer drive adaptor nut.
It screws into the side of the extension piece.
And it has a very narrow hexagon nut about 3mm high. I now believe it is 1 1/16 inch and need a an open ended spanner, because a socket pops off.
I can grind a socket down so it will stay on the nut faces I have been told.

Do you got a pic of what you’re trying to remove?

And 5C is shorts and tee shirt weather.
I’ve changed out a block heater at -40.

[jdaley]

I dont have a camera etc.
But I will try.
Heated shorts at 5C?

[wixthedog]

Still haven't got involved on my side but I think a pump wrench may be a good option, and possibly easier to find than one for bike repair. I haven't spent much time repairing bicycles so I may be off base.

https://www.amazon.com/Armstrong-28-.../dp/B00004WB91

[v30crewcab]

I just use a deepwell socket on mine. but I do have snapon sockets.

[wixthedog]

I finally got to the point where I am messing with the speedo gear and ran into to snags of my own. It is indeed a 1 1/8" socket but I did not run into any issues removing it. I used a standard 6 pt shallow socket and a quick rap on the ratchet end broke it free. I'm sure you've done it already but make sure its cleaned all around.

What I did find was a metal speedo gear, not the plastic one that I was anticipating. I made a thread in the drivetrain area asking what it is since I can't seem to Google my way through it.

[jdaley]

Now you need to remove the bits at the end of the extension piece and change a donut shaped plastic item on the final drive shaft called the drive gear from memory

[wixthedog]

So, you do not change both gears to dial in the correct calibration with the plastic 'pencil' gears, only the single gear on the tail shaft? I'll have it apart in the next couple days when I install new gaskets and front/rear seals so I'll take a look.

Google was not my friend on this one...