[53Rick]

Here's some additional information. Vehicle is a '72 GMC 1/2 ton 2 wheel drive with a TH400 transmission. I'm trying to get some advance information in case I have to replace the speedometer drive gear. The driven gear was just replaced 3 years ago. I doubt that it is already shot, but it is possible. Speedometer stopped working. The cable is good, The speedometer adapter functions properly. I jacked up the rear end and put the truck in drive with the speedometer cable and adapter removed. I can see the square end of the speedometer driven gear and it does not turn when the drive shaft is turning. At this point I believe the problem has to be the driven gear which is relatively new or the drive gear. I will, of course, pull the driven gear first and look inside to examine the condition of the drive gear. If that gear is no good, I am trying to find out the procedure for replacing it in order to determine whether it is something I can do of if I am getting into something more complicated and best done by a mechanic. I'm frustrated by the fact that neither the shop manual nor a manual on TH400 transmissions shows the procedure. Hope this additional information helps.