RPO's for older trucks?

mjsmith1223 · July 25, 2003

Would anyone have a suggestion of where to look for RPO codes for a 1986 GMC K1500?

Also, would anyone have an idea of which transmission GM put in the GMC/Chevrolet 1/2-ton trucks at that time?

The truck I'm picking up had a 305 which seized and was replaced with a 350. Should have plenty of grunt, but I'd like to know what kind of tranny and rear-end gears might be behind it. Was the transfer case on the mid-80's GM trucks any good? Most of my usage will be to drag my boat to the ramp and back, but once in awhile I like to go "two-trackin" (driving on the old logging roads around here).

Sorry to ramble on a bit.

Mike

Grand Haven, MI

Larry · July 25, 2003

Check the usual spot…the inside of the glovebox door it should be there. If not, you can yank your front seat out turn it over and you should find the build sheet stuffed between the cushion and springs.

Being that you are in Michigan where the masses don’t like to stir their own gears I can only assume this truck has an automatic. Most ½ tons with automatics after 1982 were equipped 700R4 overdrive trannies however a few TH350’s without overdrive where still around as well. The gear ratio will most likely be a 3:73 or if you are real unlucky you may have 3:42 or 3:08’s. There should still be a tag on the rear axle with the gear ratio stamped on it. Your transfercase will be a NP208 which is a pretty decent tcase for light use but tons more reliable than the push button garbage GM uses on the new trucks. If it still has the automatic locking hubs you better can those and get a nice set of manual locking hubs.

Really, the only shortcoming of a 1986 GM truck is the 5 million miles of vacuum hose to control emissions to satisfy the feds in the pre-fuel injection days. 1987 is the most desirable year of that body style to have as it had a solid front axle and fuel injection.

You might want to go here to ask questions on a truck of that vintage as this website mainly caters to late model truck folks.

mjsmith1223 · July 25, 2003

Thanks! I went over to that list you linked and it seems to be just the ticket. Hopefully we can bring some of that knowledge back here. I'll check with my brother-in-law sometime as well. He's restoring a '72 Chevrolet 1/2-ton and has probably found some of what I'll need to know.

Mike

Grand Haven, MI