I recently bought a 90 D150 w/318 & ATM, and the speedo is not accurate... Some times it shows 80mph while backing up... and going forward it's about 10mph fast. I pulled the thing outta the dash and was surprised to find it was electronic. Any way, I cleaned all contacts and sprayed with some silicone, but still have this issue... Any ideas? Is there a sending unit on the tranny that could be going bed? Thanks...

B

 

there is a sending unit in the tranny. i think there is also a sensor on the rear axel. not sure if they work together or not. the sending unit is on the drivers side of the tranny.