LMTV Backup Hand Hydraulic Pump Questions.

[CMRobots]

Hello, I haven't posted here before. My backup hand hydraulic pump on my LMTV is not getting the pressure it needs to raise my cab very well. It is leaking a little out of the top, but barely. I am thinking it could also be a little low on fluid. Any ideas? Anyone know what fluid it takes?

 

[Ronmar]

Hello, I haven't posted here before. My backup hand hydraulic pump on my LMTV is not getting the pressure it needs to raise my cab very well. It is leaking a little out of the top, but barely. I am thinking it could also be a little low on fluid. Any ideas? Anyone know what fluid it takes?

it is probably low on fluid. When facing the pump there should be a little allen head plug near the front left corner. you can fill it with AW-32 hydraulic oil. AW-32 is 10 weight hydraulic oil which is what is specced for the system. It’s the go-to oil for just about anything with a hydraulic pump in it(loaders, backhoes, log splitters ect). Hydraulic shops should have it, perhaps some auto parts stores, if you are rural, farm and feed stores should have it and perhaps even the box stores in those areas. Just don’t confuse it with Universal Tractor Fluid or UTF which is a cross between gear oil and hydraulic fluid used in the transmissions and hydraulic systems of tractors with hydrostatic drive systems... it needs to say AW-32...

 

[CMRobots]

it is probably low on fluid. When facing the pump there should be a little allen head plug near the front left corner. you can fill it with AW-32 hydraulic oil. AW-32 is 10 weight hydraulic oil which is what is specced for the system. It’s the go-to oil for just about anything with a hydraulic pump in it(loaders, backhoes, log splitters ect). Hydraulic shops should have it, perhaps some auto parts stores, if you are rural, farm and feed stores should have it and perhaps even the box stores in those areas. Just don’t confuse it with Universal Tractor Fluid or UTF which is a cross between gear oil and hydraulic fluid used in the transmissions and hydraulic systems of tractors with hydrostatic drive systems... it needs to say AW-32...

Thanks! Any information on bleeding the system of air, or fill procedure?

 

[Ronmar]

Thanks! Any information on bleeding the system of air, or fill procedure?

Just fill it. In order to move fluid, work must be happening. If you are pumping and nothing is happening, you are not really admitting any air as fluid would have to move out of the way for that to happen. Cycling/operating the system will purge any air bubbles as they pass back thru to the reservoir. Raise ad lower the cab once or twice...

Be sure you replace the fill plug on the hand pump before you start using it. It uses check valves and that reservoir being sealed to make sure the fluid goes back where it came from...

 

[Third From Texas]

The upper tank behind the cab will fill to the lower. I typically work my way between the two, filling and bleeding. Fill from the top and once it starts out the hole on the lower (use a bucket), plug the lower. Work the manual pump to work any air out of the system. Keep the upper tank topped off as you go.

It's a two minute task with two people.

 

[Ronmar]

The upper tank behind the cab will fill to the lower.

yes and no... The lower hand pump is only connected to the manifold valve(port P2 & T2, and it is not vented.

The lower hand pump can draw fluid from the upper reservoir but only if the lower pump/reservoir case pulls enough vacuum when pumping fluid out, to draw fluid past a 1PSI check valve Inside the manifold valve.

When you pump with either pump, fluid returning from the cylinder being operated has a choice of returning to either reservoir, but fluid returning to the Air op pump must overcome a 5PSI check in the manifold vlave, so the preference is to go to the lower hand pump until it reaches 5PSI then the fluid returns to the AOP reservoir which is vented...

that is why you have to have that plug in before you start pumping either pump, as without the plug installed the lower will never build pressure and all the fluid will return to the lower pump and overfill it

 

[Third From Texas]

yes and no... The lower hand pump is only connected to the manifold valve(port P2 & T2, and it is not vented.

The lower hand pump can draw fluid from the upper reservoir but only if the lower pump/reservoir case pulls enough vacuum when pumping fluid out, to draw fluid past a 1PSI check valve Inside the manifold valve. When you pump with either pump, fluid returning from the cylinder being operated has a choice of returning to either reservoir, but fluid returning to the Air op pump must overcome a 5PSI check in the manifold vlave, so the preference is to go to the lower hand pump until it reaches 5PSI then the fluid returns to the AOP reservoir which is vented...

that is why you have to have that plug in before you start pumping either pump, as without the plug installed the lower will never build pressure and all the fluid will return to the lower pump and overfill it

I only learned that they shared the upper reservoir after wondering where all the fluid was going as I filled it (I had left the manual pump reservoir below uncapped).

 

[CMRobots]

I only learned that they shared the upper reservoir after wondering where all the fluid was going as I filled it (I had left the manual pump reservoir below uncapped).

I appreciate both of your answers to my question. Adding more fluid seemed to fix the problem for a while, now I have another. The spare tire's hydraulic mechanism doesn't seem to be letting any fluid in/out of the cylinder. When I push the button for automatic movement (obviously with settings Spare Tire-Lower) it seems to be stuck, I actually see smoke come from the upper reservoir. Are there any troubleshooting/maintenance documents pertaining to this? Anyone have ideas about the problem? Note: the push button works correctly raising the cab.

 

[Ronmar]

I appreciate both of your answers to my question. Adding more fluid seemed to fix the problem for a while, now I have another. The spare tire's hydraulic mechanism doesn't seem to be letting any fluid in/out of the cylinder. When I push the button for automatic movement (obviously with settings Spare Tire-Lower) it seems to be stuck, I actually see smoke come from the upper reservoir. Are there any troubleshooting/maintenance documents pertaining to this? Anyone have ideas about the problem? Note: the push button works correctly raising the cab.

The cab and tire cylinders have safety check-valves built into them which will keep the load from falling if you should have a hose or fitting fail. There are restricted orifices in these circuits that keep the flow within the limits of the safety checks. The checks are basically a check ball centered between 2 springs, and too much flow forces the ball against a seat which blocks the flow And stops the cylinder movement. If air gets in there, sometimes it can cause the ball to lock up and if the air is under pressure, hold it against the seat. You can sometimes get it to release by repeatedly reversing flow(raise, pump, lower, pump, repeat). You can also remove the fitting and access the ball and physically force it off of the seat to release the trapped pressure behind it. you have to remove a clip, a screen, and a screw-in hollow setscrew and spring.

here, watch this

I am not sure if the port I explored in the video is the one that would be causing the lockup, or if it is the fitting located on the underside of the cylinder though, but once the screen and setscrew and spring are out of the way, you can push a narrow probe in there and you should be able to feel the ball move against the spring on the other side of the checkball... if it is under pressure, you may have to tap on it, and it may squirt fluid and air when you push it in off of the seat...

i occasionally have to do something similar on my tractor grapple when I re-connect it, if it is warmer out than when I last disconnected it. The fluid expands and you cannot push the quick connects together against the pressure. You take the male end and smack it against the side of the bucket or loader frame which forces the ball in and it squirts a little fluid and releases the trapped pressure so you can connect the fittings into the system...

 

[CMRobots]

The cab and tire cylinders have safety check-valves built into them which will keep the load from falling if you should have a hose or fitting fail. There are restricted orifices in these circuits that keep the flow within the limits of the safety checks. The checks are basically a check ball centered between 2 springs, and too much flow forces the ball against a seat which blocks the flow And stops the cylinder movement. If air gets in there, sometimes it can cause the ball to lock up and if the air is under pressure, hold it against the seat. You can sometimes get it to release by repeatedly reversing flow(raise, pump, lower, pump, repeat). You can also remove the fitting and access the ball and physically force it off of the seat to release the trapped pressure behind it. you have to remove a clip, a screen, and a screw-in hollow setscrew and spring.

here, watch this

I am not sure if the port I explored in the video is the one that would be causing the lockup, or if it is the fitting located on the underside of the cylinder though, but once the screen and setscrew and spring are out of the way, you can push a narrow probe in there and you should be able to feel the ball move against the spring on the other side of the checkball... if it is under pressure, you may have to tap on it, and it may squirt fluid and air when you push it in off of the seat...

i occasionally have to do something similar on my tractor grapple when I re-connect it, if it is warmer out than when I last disconnected it. The fluid expands and you cannot push the quick connects together against the pressure. You take the male end and smack it against the side of the bucket or loader frame which forces the ball in and it squirts a little fluid and releases the trapped pressure so you can connect the fittings into the system...

Thank you for the video as well as the information. Its really helpful. I intend on working on it soon, seeing if your suggestions might be the reason why the cylinder is locked up. I also plan on rebuilding the air over hydraulic pump while I am it.