Antique hydraulic system quit - how to diagnose

[lhfarm]

I've posted here before about the hydraulic system on my 1949 Jeep. The simple system is a pump driven off the crankshaft. Hoses run to the rear of the jeep to a control valve, cylinder and the reservoir. There is no way to determine the fluid level. The fill tube is just below the top of the reservoir and has an elbow with a plug. I fill the reservoir to the top. I recently put a new seal in the front of the pump. The pump appeared to be operating correctly and would lift me (200+ pounds) without a problem. Today attached a 2 bottom plow and the pump lifted the plow with not issues. I then lowered the plow and it would not lift more than a couple of inches.

I thought I need to add fluid (hadn't added any since installing the pump) and maybe take the plug off the filler to let air out. Tried several times and no change. Took the plow off and ran the lift up/down several times. Finally, if I greatly increased the engine speed the lift seemed to work.

There are no leaks at the pump and I did tighten connections at the control valve and at the reservoir return line were it appeared there might be drips. I do not have access to a pressure gauge. Based on the behavior above, can anyone suggest next test steps? Since it seems to work with greater engine speed, is it possible it is still sucking air?

Any help appreciated.

 

[David Devuono]

The pump may need a rebuild, ie leaking internally. I know my 1960 something MF135 needed to run wide open to get anykind of hydraulic flow. Unfortuneaely the tractor did not like hours of wide open running with no load other then the pump.

 

[J_J]

You pump could be totally worn out.

If it is not pumping about 75% of rated flow, then it is time for a new pump or a rebuild.

You could do or have someone do a flow and pressure test where they put a load on the pump to check it's performance.

 

[lhfarm]

It is very possible that the pump is worn out. However, because it worked perfectly 1 minute and then didn't the next (lift the plow without a problem, but when lowered, couldn't lift it a second time) is it also possible that the problem might be in the valve? Here is a thread where I took it apart to clean it - http://www.tractorbynet.com/forums/...d-help-rebuild-little-control.html?highlight= If something is sticking in the valve, would that give the same symptoms as a worn pump?

Since this is an antique show piece, I'd like to use original parts. But since the valve can't be seen (it is under the bed of the jeep) and I'd like the lift to be functional, I could try to rig a modern control valve. Can you recommend a simple control valve for this setup (single action cylinder with power up gravity down)?

Thanks,

 

[J_J]

If you can't find a cheap single action valve, then use a DA valve and plug one work port, or run the work port to tank.

 

[wdchyd]

The symptoms you describe I've seen worn out pumps do exactly the same......many times

when cold (first started) they pump barely enough to work, then as the pump warms to operating temp there is too much wear and clearances in the pump....leading to less pressure the more you run it.....also revving is another sure sign of a bad pump

Flow/load meter will prove this beyond doubt

 

[lhfarm]

The symptoms you describe I've seen worn out pumps do exactly the same......many times

when cold (first started) they pump barely enough to work, then as the pump warms to operating temp there is too much wear and clearances in the pump....leading to less pressure the more you run it.....also revving is another sure sign of a bad pump

Flow/load meter will prove this beyond doubt

I have a NOS pump that leaked from the shaft when I tried it a couple of years ago. I've ordered a new seal and will give it a try. It might be a couple of weeks before I can make the switch, but I'll report back.

Thanks,

 

[lhfarm]

Finally had a chance to look at the pumps. Ordered a new seal and took the NOS pump apart. It doesn't use the same seal (maybe just an O ring?). Put it back together with new O rings in the manifold that appear to have shrunk after setting for 60 years (hoping that was the source of the leak) and started to mount it in place of the old pump. When I removed the old pump, it has a bad leak around the shaft. This was the seal recently replaced. Not sure if I damaged it when doing the install OR if it blew out for some reason. But that would explain why it suddenly quit working.

Since I have a new seal, I'll put it in the pump and try it again.

Thanks,

 

[lhfarm]

Update - I installed the new shaft seal and the pump stopped leaking. Hadn't had a chance to test the system until today. The pump lifted my son and me (excess of 400lbs), so we hooked up the plow. Lifted perfectly, so we moved the plow. Lowered it and it wouldn't lift. Fluid leaking from the pump again. Leaking around the same shaft seal.

So this is second or third seal that has blown and I'm wondering if it is a relief valve problem? Assuming the pump is building pressure until it blows past the seal.

I've ordered a couple of seals, but figure I need to determine why they are blowing before I put a new one in.

Suggestions for next testing steps?

Thanks,

 

[oldnslo]

Look for a vent passage from the seal cavity to the pump inlet. Make sure this passage in open and or clear of any debris. It only takes 15 - 20 PSI to blow seals and possibly less. Once the shaft seal is blown the pump will suck air and stop working and go into the slow death mode of cavitation.