The Stovebolt Site Forums The Shop Area Driveline SM 420

Does the speedometer drive just screw into the SM420, if so does it come out easy? I have a speedometer that jumps around a lot but I think its the speedo head itself. but thought I would check the gears on the drive to make sure. 53 3100 root

There is a gear that can be unscrewed from the case of the transmission (to inspect the teeth). There is a gear inside the rear of the transmission and it cannot be removed without removing the u-joint yoke at the rear of the transmission.

It does on the SM420 on my 54 3100.

Checking the gears is a good idea. I had to use a deep thin walled socket to remove the speedometer cable drive. The other gear is held in place by the u-joint yoke. Speedometer gears rarely wear out though. The problem your having is more likely a wore out speedometer head, as was the case on my truck, or it could be the drive cable. Jim Carter Truck has refurbished original speedometer heads. I would avoid the Chinese reproductions. they also have the cables.


Walt Williams

Well Walt, I think you've miss understood what Tim replied.
The 'drive gear' is pressed on to the yoke or U-joint flange
and can only be removed by removing the yoke and pressing the
drive gear off.
http://www.pbase.com/dennygraham/image/148876672
If your's slips on and off the flange then something is worn.
If it were not a press fit, what would keep it from slipping
on the flange when in motion?
So....I believe you're thinking of the 'driven gear' which can
be easily removed with a 15/16" box wrench.
http://www.pbase.com/dennygraham/image/160677688
dg

My bad, yes it is the driven gear. I will remove and check it out for damage. Thanks y'all. root