[Keith Seymore]

Originally Posted by roboticjunky

None of those rpo codes are for the axle ratio. For the axle it would be Gxx or Hxx. Here's a listing of axle rpo codes.

https://www.differentials.com/gm-axl...ication-codes/

This is correct.

Additionally, if the truck has the base ratio it will not appear on the SPID or will show "GQ8 - Base ratio". If the person who ordered the truck had chosen an optional ratio then those typically do appear on the SPID with the corresponding RPO.

Per the powertrain chart in the generic info packet the base ratio for a '78 C10 with L59 and federal emissions is a 3.07 (HE3).

https://www.gm.com/content/dam/compa...olet-Truck.pdf

K