Manual pump pushing the fluid to air/oil pump

[aw113sgte]

When using the manual pump for any operation, it will run empty and not pump any longer. Thinking the fluid might be a little low, I refilled the manual pump tank, but I'm noticing it's pumping fluid into the air over oil pump reservoir, this caused it to overflow. Guessing is a check valve somewhere that's leaking?

 

[Ronmar]

First off the pump is performing the work you are asking of it(raising cab or spare tire), correct?

there are a set of steering check valves in the system, but they are on the return to the air op pump(circled in red). The hand pump is sealed, so when you pump fluid out of it, it goes into vacuum. Returning fluid must pass thru a 5 PSI checkvalve to get to the AOP so it will always want to steer fluid back towards the hand pump in an attempt to keep it topped off. Once the return fluid goes over 5PSI, it can then flow toward the AOP reservoir.

i suspect you have a kinked/collapsed return line to the hand pump, or a clogged return filter on the hand pump forcing fluid towards the AOP thru the check-valves. Even if one of the checks was stuck open the hand pump going into vacuum would still want to suck return fluid that direction. In fact if it goes into deep enough vacuum, it can draw fluid from the AOP reservoir thru a 1PSI check…

 

[aw113sgte]

The pump does work normally until it runs out of fluid. Thanks for all the other info. I'm not sure mine is a sealed system as there is a short metal tube to the right of the handle. I think this may have been and a1 change as others I've seen have no tube?

 

[Ronmar]

Got a pic of the pump? The filler is usually a allen plug, front left when facing the pump. If it wasn’t sealed it would overflow whenever the AOP is used as the return pressure needs to get over 5PSI to find its way back to the AOP reservoir…

 

[aw113sgte]

This is the one I have. That little metal tube sure looks like an overflow.

 

[Ronmar]

They make different variants of this pump, and on some that is where a control valve is located. Does that “tube” handle and the piece it is connected to rotate? It should be able to rotate clockwise 180 degrees It looks like it is bent down as it should point straight back. it reverses the functions of the two ports on the pump, so that pump could be used to extend and retract a cylinder just by connecting the two cylinder hoses directly to it. In this application with the LMTV using an external valve it would only be used in one position, as the hand pump, like the AOP only needs to supply fluid in one direction. In your pic it appears to be in the correct position, and the lower pump port should be the output port…

if it rotates, you could disconnect the two lines attached to the pump, rotate the lever 180 deg clockwise/lever pointing outward and pump a few times to backflush what is normally the return port on the hand pump, then re-attch the hoses and return the control lever to its inward/normal position.

the older pumps don't have the control lever.

 

[Ronmar]

Here is one with the control lever...

 

[aw113sgte]

Well you were right about it being a valve. Looking closer it appears to be an intentional bend in the little lever. It rotates 180 degrees easily and it appeared to back flow. Still seems to run itself dry though when I put back into original position. I'll work on checking that return line next.

 

[Ronmar]

If you disconnect the return line at the hand pump and fluid comes out of the line while pumping, the problem is probably still in the return side of the hand pump. If fluid does not return thru the line when pumping, then it is the line or something upstream...

 

[aw113sgte]

Hand pump is not pushing any fluid out return port, return line is sending fluid to pump.

There was significant restriction blowing into the return port. It appears on the bottom of the direction selector there is a very small orifice fluid has to pass through. I removed this and replaced the fractured o-rings. It does seem to work better, but still runs out of fluid after doing the cab lift a couple times.

When I removed the reservoir fill cap, the reservoir did refill when moving back and forth with the air over oil pump.

Seems like it is not refilling the reservoir at the same rate is pushing fluid out. Since at the end of cylinder stroke, the pump will ever gets hard and will not leak down to me that indicates there's not a leak path on the pressure side.

 

[GeneralDisorder]

I have never seen a pump with that selector lever on an FMTV. My truck is a 2008 A1R and doesn't have that lever.

Very strange. Since the lever serves no purpose but to complicate the situation I would get a normal FMTV pump and swap that one out.

 

[aw113sgte]

How do I take apart the pump seals? I've se n the ones with a hex and those can be spun off. With the circular top fitting I can't figure out how to get it off. It spins but doesn't unthread

 

[Ronmar]

I am not sure of the specifics of overhauling that hand pump.
when you lift the cab, you send more fluid to the base end of the cylinder per inch of travel than is returned from the rod end because of the amount of fluid the rod displaces.

the hand pump being sealed should go into a vacuum and draw fluid from the AOP as soon as you send out more fluid than is being returned. It get fluid from the AOP via that 1PSI check-valve I circled in the above drawing. If the hand pump case, the filler plug or even that control valve body was not able to pull a vacuum, or that 1psi check is clogged, the hand pump might have trouble making up for the difference in cylinder flow to-from when lifting the cab…

it is way easier to suck in air than draw fluid, if it is drawing in air, that air displaces fluid and keeps the hand pump reservoir from refilling and it will send fluid to the AOP with each cab lift/lower cycle…

 

[Ronmar]

Your problem could also be as simple as a loose fitting or pinhole in the return line that is keeping you from pulling a vacuum and delivering air to the hand pump reservoir instead of fluid…

This design always struck me as mickey mouse. They really should have just run the return line thru the sealed hand pump reservoir on the way to the AOP reservoir. Then the hand pump would always be topped off, and it wouldn't rely on pulling enough vacuum to pull fluid past the restriction of the check valve in the control valve assembly…

yet another reason I am not sorry I removed all of mine and replaced it with a dual acting hand pump. I only have cab lift, but a basic 2way control valve would allow me to do cab and spare tire crane if I was still carrying my spare that way…