1976 Chevy Stock 4x4 Question

[blink32]

I'm brand new to 4wheel drive. I just bought my grandfathers 76 4x4 after his passing. Besides fixing safety issues and tackeling leaks here and there I'm going to replace/repair/relube all the ujoints and differentials. I've done the rear with all new seals and oil, the bearing and such are good to go. Next is the front diff.

My questions are these. What is the best/correct way to engage 4wd high and low with the manual hubs? How I have been told is to get out and lock the hubs, then just start driving and push in the clutch, slide the 4wd lever to 4h, let the clutch back out and continue driving and ****ing as normal. I've got the M20 4spd by the way. After reading the pickups owner's manual I'm kind of under the impression that I don't even have to use the clutch to engage 4H from 2H. Is that correct?

And what about disengaging 4wd? After a drive to my girls farm in Jersey the pickup was warm and wend into 4wd easily and made no excessive noise. And I know it was engaged because on tight turns I could feel the wheels "skipping" over the dirt from the differential being locked. But the next morning it was about 7 degree's out and there was a godawful noise coming from the transfer case as I backed up and as I drove forward. It also made a hell of a rattling racket when just left to idle. After getting it in 2H and driving for a few minutes it seemed like the gears fully disengaged and everything was normal.

I've pretty much resigned to the fact that I'll have to rebuild the transfer case at some point. I just want to make sure I don't hasten that event.

[1969 GMC]

On my truck, I have found the easiest way to get it into 4wd is to lock the hubs, then drive a bit. Push the clutch in (it says in the owners manual you only have to do this when putting in 4Lo, but I do it every time just because...I'm sure it doesn't adversely affect anything) and shift into 4wd. Then when you are done, put the shifter back into 2wd first, drive a bit, then get out and unlock the hubs.

[blink32]

What about transfer case/trannie identification? I haven't figured it out 100% but I think I have an NP205 transfer case and the M20 trannie is also known as the SM465? Is the trannie also known as a TH400 by any chance? I did a bunch of searches but I was unable to figure this out.

[1969 GMC]

as for your transfer case...I am not sure, but it could be a NP205. What is the shift pattern for it? if it says something like "hi" "hi lock" "lo" lo lock" then it is a NP203 full time transfer case, which is more common in 73 up 4x4s. But if it just has the standard shift pattern (4 lo, 4 hi, 2 hi) then its a NP205.

your transmission is the SM465. its RPO code is M20, but its totally different than the car version. it has the granny low first gear. the TH400 is an automatic transmission, you said you had a clutch pedal so I'm fairly certain you don't have this.

[blink32]

Yeah, no Hi and Hi lock or anything, just 4wL N 2w Hi 4wHi and yeah, i've got the 4spd with granny gear. thanks for the clarification. I figured I had correct info but I wanted to make sure. Thank you again.