Ever since last winter, I have not been able to use 2H on my '78. Its the standard 4 speed manuel and when you shift it into 2 wheel high, once you start to move forward it pops out of 2H and into neutral. I have been running in 4H with the front hubs free, not exactly what you want to be doing. Any suggestions on what might be causing this? Checked the fluid level and its good.

 

Check your shift linkage to see if it is loose or binding. If that checks out fine the internal shift mechanism is faulty. Requiring a rebuild.

 

 

I agree that it is probably the shift linkage. Sometimes the nut that holds the shift linkage at its proper place will loosen and allow the linkage to come out of adjustment. To check the adjustment, go under the vehicle (while it is not running!) and attempt to move the linkage by hand. You will see where the rods attach the the case, and where they attach should be a piece that can move back and forth (it attaches to a shaft that goes into the case). You should be able to grasp the rod and make it move that piece. If it is adjusted properly, you should feel the rotating piece click into position. It should click easily into position, without forcing. If you can move it a little but it does not seem to go all the way, or it goes but is hard, then the linkage is out of adjustment. Since your transfer case goes into gear, but pops out, then I would guess that it is out of adjustment by a single turn or two. Any more than that and it would not go at all. Also, it may be helpful to have someone in the truck move the shifter so you can see if the linkage is binding. Adjustment of the linkage is simple. First, make note of where the piece that goes into the case is when the truck is in 2WD. Then, remove the linkage from the piece. Once you remove the linkage, make sure the shifter is also in 2WD, and hold the linkage up to the piece on the case. You will then see where it needs to be when tightened. Mark this area or eyeball it, whatever, but this is where you will have it when you tighten the locknuts back down. Check it for movement, and you should be good to go. This is harder to put into words than to show, it's really easy. PS - THESE INSTRUCTIONS WORK ON MANUAL TRANSMISSIONS, I AM ASSUMING A TRANSFER CASE WILL WORK IN THE SAME MANNER. SO SOMEBODY CORRECT ME IF I'M WRONG. IF THESE HAVE CABLE SHIFT LINKAGE, THEN YOU PROBABLY HAVE A STRETCHED CABLE.