gearbox/speedometer trouble

[59gmc]

I am in need of help as my speedometer does not work in my 59 GMC stepside3 speed manual.
I have traced the problem to the gearbox .
The speedo cable and the drive that goes into the gearbox are in good working order.Both when manually rotated do make the speedometer work.
I removed the speedo drive from the gearbox and on feeling inside was unable to find the gear or cog that would rotate the speedo drive unit.
The shaft that would normally hold that gear or cog does turn when the prop shaft turns.
Has anyone got a diagram of the internal workings of the rear section of the gearbox that holds the speedometer cable and drive unit?
This would greatly assist me in removing that section from the vehicle.
Many thanks for reading

[dwcsr]

its a pretty easy deal. drain the oil, remove the drive shaft, unbolt the 5 bolts and remove the tail shaft housing and your there. you should see the helical gear either missing or just flopping on the shaft. it should have a spring clip that holds in in place. If its missing altogether PM me.

[59gmc]

Many thanks . In the next week or two i will have a look and get back to you.
Thanks again

[59gmc]

I have taken off the tail housing and the helical wheel for the speedometer is still there but does not seem to have a securing key/clip. I will try to locate one over here in the UK. Is anyone able to tell me the type of gear oil the gearbox should have and the quantity required?

[55dude]

90 wt gear lube same as rearend. their should be a plug that looks similar to the drain plug on the side of the transmission. fill until oil runs out of this hole

[59gmc]

superb and many thanks

[59gmc]

All sorted and put back together, went for a drive today and it was superb to see the speedo guage working properly.That is one more problem off the list -on to the next one!
Thanks again to you all