1980 K100 Cabover Project/daily runner

Maybe try using a comealong. Pull on it, then pump the jack and repeat. Don't force it and if you unhook the lines you could end up in a free fall. Many have some check valves in the system and can get you jammed up. An air jack is the way to go. Especially on those double bunks.

 

I do not recall the brand. Used to buy them from the IHC or KW dealer. Also from Mathews equipment in Atlanta.
You could have a safety valve stuck in the cylinder. It has been along time but seams like some times you have go the opposite direction and then come back. If it's not to far over you could maybe pull the pin-pins out of that cylinder and just use the other one. Always keep safety in mind. We used to use pipe and or load locks under the cab like a jack stand.

 

Brand is power packer, they are still made and sold. Most popular place is Ohio Hydraulic, at least I think that is the name.

I think the air/manual pump is $6-700, the manual pump is around $300.

 

I had the same problem on my Pete, would jack up easy enough, but wouldn't come back down. Turns out there are brass check valves in the valve body with really small ports. These ports will plug up with debris (old fluid crud) that develop and collect over time. You'll have to carefully take these check valves out and thoroughly clean them and the ports, drain the system, and replace the fluid. I used ATF type A to replace it. You may have to drain and refill a couple of times to flush out all the old fluid/debris. Once I cleaned it all out, it worked as it should. Be careful and make sure you engage the cab safety latches and block up the cab before messing with it....

 

Not sure on a KW, but on my Pete 362, it's right next to the hydraulic lift cylinder (right side) and latch in once the cab gets to its height. I'll try and get a pix for you. Those little brass check valves have ports that are very small to allow the fluid to pass. It doesn't take much to plug them up, similar to the jets in a carburetor....