What transmission/transfer case do I have?

[willem445]

Its a 1980 Chevy K20, 10 bolt front axle, 14 bolt rear. For the transmission I've got L, 1, 2, 3, R and the transfer case has 4LO, N, 2HI, and 4HI in a straight pattern. What oils should I use to replace on each?

EDIT: Also what is the best oil to use on a worn Chevy 350 5.7L w/ ~80k miles.

[jhama78]

I assume its a 4 speed manual? in that case Id bet that its an SM465 granny gear 4 speed and a NP 205 tcase.

If it were mine I'd use a name brand gear oil in both. I'm sure that somebody will pipe up with the recommended weights but 75w90 or 80w90 should suffice. both of those components are well made gear to gear heavy duty units and will tolerate a lot of abuse.

So far as engine oil I like Rotella 15w40 in older engines. I run it in my 67 and my 86 with no problems.

[74CustomK20]

I also run 15w40 and 80-90 gear oil. Been doing fine since I got the truck a few years ago.

[willem445]

Yes it's a manual. Thanks!

[Dead Parrot]

If the engine truly has only 80K miles, use 10W-30. 80K isn't that many miles unless the motor has been abused or ignored. Now if the odometer has rolled over a few times, a heavier oil can slow the leakage and help with oil pressure until the motor is overhauled or replaced.

[andrewmp6]

Or you can crawl under your truck on the t case theres a round metal tag that will tell you witch t case you have.

[Matt Man]

I recall 1980 models only having the np205 case.

[andrewmp6]

I think your right 80 was np205 only but its a old used truck someone could have swapped t cases over the years its best to know for sure what you got.

[hatzie]

The only stock case in the 1980 is the NP205 that uses 85W90 GL-5 gear oil. Some K30 with Auto Hubs got synchronized gearshifts. Use GL-4 in the Synchronized cases.

The 1979 & prior NP203 uses SAE30W non detergent

The 1981-1988 NP208 uses AC Delco 10-4033 or GM 88861800 Manual Transmission Fluid. Mobil1 ATF with GM 88861800 listed on the label or Pennzoil Synchromesh fluid will work. Usually the Delco fluid is cheaper unless you're buying from the dealer.