Is there even a 3-speed with overdrive for closed driveline? The SM318 is a non-overdrive tranny. The speedometer gear on the main shaft can come out once the rear yoke has been removed. The driven speedometer gear just unscrews from the side of the tranny tailshaft.
Last edited by klhansen; 11/21/20234:19 AM. Reason: fixed spelling
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
As long as the gear spins true it should be good. I had one that the shaft bent a little and the gear wobbled.
~~ Jethro 1954 3100 Back to Life In the Dity Gallery 1951 3100 (gone) / 1956 4400 (still in the neighborhood) / 1957 6400 with dump body (retired) / 1959 3100 panel (in the woods junked) / 1978 Custom Deluxe K10 / 1993 S-10 4.3 / 2004 Chevy Crew Cab / 1945 John Deere H / 1952 John Deere B / 1966 John Deere 2510 / 1967 John Deere 1020
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.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
