Transfer case won't shift in 4L

[Pachyderm]

I've got a 73 J4500 with 3spd manual trans. I've got trouble with the Dana 20 not shifting into 4L. Shifter wouldn't move the inner rail on D20 at all. I removed the shifter and it moves fine when disconnected from the D20 shift rails. I pushed the inner rail on the D20 in but it was a lot harder to move than the outer. I'm thinking that I've got to overhaul the transfer. What do you all think? I don't have any leaks and the case is good on the outside, just really dirty. I have never done this before so I'm nervous about tearing into it....especially since it has a Ramsey PTO sticking out the bottom of the transfer. I was thinking if I do and I've got to drop each shaft, might as well replace the U-joints. The parts catalog lists all the u-joints as 4485624. I am confused about replacements... I get different answers depending on where I look. What do you all recommend. BTW, I've got the spicer shafts with 132" wheelbase. Was told by PO the front axle was Dana 44 and the rear was Dana 60 but I have yet to verify.

[Stuka]

To get into low range, its not unusual to need to have the vehicle slowly rolling while in neutral (or clutch pushed in). The low range gears are straight cut, so they don't always mesh nicely. You have to kind of pop them in as they are slowly turning. The D20 U shifter can be a bit finicky if worn out, but more comes down to just knowing its a U. Straight back for 4wd high, and then push to the right and forward to pass through neutral and into 4wd low.

I see you mention the PTO comes off the transfer case, this could actually be an additional reason that it won't go into low. For the PTO u-joints, best to just measure them. Spicer and Moog make PTO u-joints in various sizes.

Your axle should be a D44/D60 for a J4500. Most likely 4.10 gears as well.

[Pachyderm]

Thanks! I took the shifter apart an cleaned and regreased which helped a lot. While I was working on that I decided to check the poppet spring and ball. After cleaning the crud off, I found orange plastic caps covering the holes and when I popped them out, I found empty threaded holes. The parts manual shows the diagram of what goes in but it has the order with the spring in first, then the ball, then the plug. Is that right? It doesn't make sense that way. I ordered the springs and balls from Morrix 4x4 but I don't know what to do about the plug. Will a standard bolt work? The parts manual has two listings. 7/16x20 and 9/16x18. I think mine is the larger hole. It doesn't give the length. The hole only seems be be about 1" deep so the plug must be short. Can anyone help me with the sizes?