Speedometer gear replace
Thread Starter
Instructor
Joined: Sep 2010
Posts: 229
Likes: 1
From: Grants Pass Oregon
Speedometer gear replace
I bought a '78 ,L48,Auto. Speedometer didn't work. Checked speedo,cables.tranducer, all seem to fine. Pulled speedometer gear ,19 teeth??? How do i find out what gear is the right gear? Thanks
Burning Brakes
Joined: Feb 2001
Posts: 929
Likes: 5
From: Marietta GA
It's been a while since I've dealt with these issues. There are two gears that mesh together to give the proper turning speed to the speedometer cable running from the tranny to the speedometer. The drive gear (inside the tranny) and the driven gear (inserts from outside of the tranny and is plastic). First you need to determine how many teeth are on the drive gear (the one in the transmission). Over the years they have been either plastic or metal. You can remove the driven gear from the side of the transmission and look inside the tranny with a flashlight, slowly rotate the tranny and count the teeth. Then, depending on your tire size and final drive ratio (differential ratio 3.08, 3.36, etc.), you can choose the proper plastic driven gear. They are color coded, with different color representing a different number of teeth. Either search the archives here on the forum or on the internet and you should find a speedometer gear calculator that will tell you which driven gear you need.
Thread Starter
Instructor
Joined: Sep 2010
Posts: 229
Likes: 1
From: Grants Pass Oregon
speedo gear replace
Thanks for the info. I took the gear to my local chevy dealer, and they said the gear looked ok. so i guess it's the one inside.I couldn't see the other gear. I've got headers with 2 1/2 in. pipes. Took me forever to get the gear out. May have to go to trans shop. Thanks again.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
If you got the driven gear out, then it's no step to the drive gear- pull the driveshaft and 4 bolts that hole the tailhousing on. Even if the rear mount is on the tailhousing, just stuff a jack under the pan and lift it up a little.
(unless it's a 200-4R)
(unless it's a 200-4R)
