Hi all. My first post here but I have read the forums quite a bit with all the old junk I own. I have a 1986 F800 that Im having a hydraulic issue with. I had to do a bellhousing gasket on it, so I pulled it in the shop and got to work. This truck has a pto shaft that connects the hydraulic pump to the pto. When I finished, I hooked the shaft back up, backed out of the shop, tried the pto to verify I had the linkage to engage and disengage it right and now the box wont go up. Now, there is two shafts on this pump, one clockwise and one counter, I know for a fact (because I never removed the key) that the shaft is on right. Both shafts turn as they should. It sounds like there is no oil, which doesn't make sense because it didn't all run out on my shop floor. My buddy (who is an ag equipment tech) helped me out as well and we are both left scratching our heads. This is a closed system, the cylinder is the reservoir. We topped it off (didn't take much), pulled the suction line to verify oil delivery to the pump. pulled the valve spool, have oil there, pulled the plug on the side of the valve, have oil there, tried running it with the fill port out to release any air, still no dice. I pulled the pump off, tore it apart, absolutely nothing wrong with the pump or valve. Where do I go from here? I need this thing fixed and back in service asap. I also cannot identify the pump, I will try to get a couple pictures up of it. The pump and valve are the same unit as well with this.
Have you tried air pressure in the fill port to see if that will make it prime?
No. Never thought of that. My buddy talked to a local Hydraulic guy today this guy said those pumps are finicky and definitely has air in it. Never thought of forcing air into the system to prime it, makes sense enough, if I can get it to pick up any oil and start to pump I would think it would take care of the air by itself.
When you pulled the transmission did you have to disturb anything on the pump other than the driveline? If not are you absolutely sure you got it back on the right shaft stub? I read what you said, but sometimes...
Absolutely 100 percent sure. My thought was I aggravated something in the pump pulling the shaft, so that's why we tore the pump down, after getting the pump apart there is no way of disturbing anything, stupid simple design. It's not the pump and everything is turn ing as it should but not moving oul
definitely still sounds like air. If you can't get it to go with air pressure on the reservoir, then open the oil hose to the cylinder, turn the pump shaft by hand, with the air still on the reservoir, until you get a steady flow of oil, then put it back together and start it up and try it.
Ok guys. Got the pump reassembled and installed. I have tried everything. When I cycle the valve with the plug on the pressure side of the valve loose, I get air out of the system for a second. When the valve goes back to the lower position it's almost as if it sucks air. There is air being Introduced at the pump or the valve I believe, I'm just not sure how. There are only two o rings in the valve spool, those are new, new gaskets in pump. Only thing I haven't replaced are the seals on the input shafts. Could that be the issue? There is no oil leak there so I don't see how it could suck enough air to have zero flow. I just don't get why it worked one day then a week later next time I go to use it absolutely nothing. I can't find anyone around here that understands the underbody hoist type system. Remember the reservoir in this system is the cylinder....I am at a complete loss. I'm about ready to replace the pump and valve, I can't even figure out where to go from here.
It doesn't need to keep sucking air to not work. it can suck in a little bit of air over time, then refuse to start up until you force fluid through that pump to get rid of the air. Air will not seal up the clearance between the gears and the housing, and that gear pump will NOT pump air. The input shaft could be contributing to this, a new pump MIGHT not have had this problem from sitting for a week, BUT by the time you need to mess with it again, the new pump might do the same thing. You have to get oil flowing to fill the pump with oil, it's that simple and that tough, you're going to have to open some lines and spill some oil. Don't do it with the engine running. I'd do it by turning the pump by hand, you could use air pressure instead.
I'll try that. We tried cracking the pressure line but got nothing. Was thinking of trying to lift the box with the skid steer with the pump running to try to force it to take oil.
if you use the skid steer, lift the truck bed up and down with the valve in lift, AND lower positions.
So far all we have here is that you disconnected the driveline to the pump before this mess started. Are you DOUBLE, TRIPLE, QUADRUPLE sure the rotation hasn't been accidentally reversed? When a gear pump is operating oil flows around the outside of the gears with the gears turning towards the inlet where they are in mesh. I had a guy screw that up on five wet kits once and spent hours in a gravel parking lot on my back changing the pumps over.
No possible way it got screwed up unless something in the pto itself got messed reversed but I don't even see how it's possible. There ls two shafts on the pump, top and bottom, it is supposed to be on the bottom. The top shaft is buggered up and you can't get a key in it, been like that for years so I'm positive it's correct. We even tried it on the other shaft when this first started just to rule out me being an idiot and unfortunately it made no difference.
Got it. Through some screwing around and bleeding lines we finally got it. I guess it was just being stubborn. Now the pump has basically a fresh rebuild for a few dollars worth of seals. Good to go now. Thank you for the help.