The Stovebolt Site Forums The Shop Area Engine Shop speedo driven gear

hi y'all,

working on little things now. on the speedo cable driven gear. i have removed it from transmission. it is a 12T. is this a press fit into this housing which threads into the transmission?? problem is speedo not working. i have run cable with drill motor and both odo and needle move. if i connect cable and driven gear to tranny-remove cable at speedo--observe cable not turning when driving down road. right now i think either the teeth on driven gear are wore down or gear on trans shaft are wore.

not sure i want to crawl under truck and observe with rear wheels turning,truck in gear and engine running to see if exterior end where cable goes is rotating. any suggestions where to get driven gears??

also i have been trying to ID transmission. I have 51GMC 1/2t LB with 228/6cyl and 3 speed on column. i cannot match the casting numbers with other websites to ID. casting number on linkage side is 3686832 GM 23, casting number on passenger side is E31 GM 591616. Stamped number on rear driver side is J0I4450. ANyone know what kind of tranny this is?? Think is Saginaw 3 speed but not sure.

Hey I just went through ALL OF THIS and WHAT A HEADACHE! I located a BRAND NEW MATCHED set of speedo gears for a 48 passenger Chevy to put into my original torque tube '54 three-on-the-tree Muncie. The fellow I got it from is CHAROB Industries in the San Fernando Valley and he (Charles or "Chuck")has one more left, brand new matched set NOS, which is what you need. What I found was on both my old trucks the drive gear on the tranny output shaft was worn. Had to rebuild the entire tranny. At the moment I do not have his phone number but his address is 11267 San Fernando Rd. San Fernando Ca. 91340. The speedo works perfectly well now(despite being off just a tad!) and the old truck finally clocked its first mileage in 23 years. These NOS matched gears are getting REALLY HARD to find so I wouldn't wait to procure them. Took me weeks to locate them myself and trips to all my local speedo shops.

update.

after talking with guys at auto shop in town, another customer pointed me in direction of small junkyard s ome 20 miles away. went and owner knew right off what i wanted, went over to cobbled up lawn tractor and unscrewed driven gear and it was exact match and not worn down like old. i said how much and he said $2 but he wanted old one to plug hole on his machine.
i thru him $5 and left. n this has fixed the "turn the cable" problem, but now i must work on speedo. i can get the odo "ten'ths" to drive but no other milage numbers turn when it goes from 9 to 0. also speedo needle will not move. this is odd since the needle would move when i spun cable with drill motor.

still have not id tranny.

Those casting numbers are from a '48-'54 commercial 3-speed, according to the Chevy parts manuals. The JO prefix in the serial number confirms a 3-speed from a '51 3100 series Chevy (not sure if the prefixes were the same for GMC), built at Muncie. I don't know if these early 3-speeds were designated as Muncie or Saginaw, though they were built at the Muncie, Saginaw, and Toledo plants.

The speedometer head (or gauge) needs to be cleaned and rejeweled. Take it out and take it to a speedo shop. They can clean and rebuild it for you. Older speedometers wear out the permanent magnets inside, they need to be replaced. Sounds like your odometer needs to be looked at too. It doesn't cost that much to have it fixed.

thanks everyone,

i did shorten the cable and got the needle to register-but still does not seem very accurate.

will extricate and take to speedo shop for repair.