The Stovebolt Site Forums The Shop Area Driveline Speedometer gear

Jim, They do occasionally go bad. Easiest way to check on the condition of both the speedometer drive and driven gear is to just remove the driven gear from the tail shaft housing. Guessing you are working on your "new to you" transmission? The drive gear assembly looks like the pic attached below. Unscrew the assembly from the tail shaft and inspect the small gear housed in that piece for damaged teeth. With that assembly removed, look inside the housing and inspect the teeth of the drive gear to look for damage. Be sure to turn the output shaft to see the entire gear. If both gears are good, nothing needed. If either are damaged, you will need to count the teeth on both to determine what to look for as replacements.

Best place I have found for replacement gears is on eBay although they may be found elsewhere. I have seen NOS gears available, but there are a number of different gear sets so you may have to do some research or get help to identify original GM part numbers.