no lift pressure all of a sudden

[seanpaintsflames]

Good morning! Here is the latest chapter in the poor elderly tractor story.
The 53 Jubilee runs awesome. Strong, good oil pressure, the lift and the loader are working great and reliably. I park it, shut it off, and then slowly push the quadrant control down to lower the mower so it doesn't just leak down. In my mind this is better than leaving it hanging up there, but doing so after the motor is off could very well be bad for it without knowing for sure... SO, I go to start it up the next morning, and the lift is completely dead. I have a 3000psi gauge hooked to the extra port on the cover that read 1700 or so the day before, now reads 0. Up or down, stays at 0. Draft control makes no difference. I pulled the acorn nut and backed off the valve thinking it may do something to help me. No change. What now?!?

 

[Cvans]

No answer but I sure hope you figure it out.

 

[bumperm]

Just a WAG ('cause I really don't have a clue), but have you checked hydraulic fluid level? Or maybe a leak somewhere that is allowing the hydraulic pump to suck air and cavitate?

bumper

 

[Soundguy]

1, moving the 3pt hyd lever after shutoff has NO EFFECT on hurting anything in the system.

you can se there and yank on that handle for 20minutes while she's off and all you will do is make your arm tired and put some microscopic wear on a metalic pin and cam.. in about 60 years it will be enough wear to replace it.

2, the port on top of that option cover won't show you pump pressure unleess it is working against relief.. and it won't show you operating pressure of the lift curcuit under load.. untill it is UNDER LOAD.

the system uses an unloader circuit. basically.. at any time when the lift is not up.. there won't be any more than about 40psi back pressure ont eh lift circuit as hyd fluid flow from the pump is dumped to the sump.. just enough pressure is maintained to keep the unloader alive.

ensure you have hyd fluid.. ( dipstick ). if you have fluid.. but no lift, pull the plug out o fthe head of the pump if it is a cylindrical piston pump and crank over / start at idle and see if you get oil there. if yes.. shut down put plug in and see if the lift magically works. if yes.. it lost prime.. a couple reasons. if you are lucky and living right.. it is the oring ont he plumbing manifolds on the suction side.. or a pinhole inthe suction line.. otherwise.. it's probably a shaft seal in the pump.

now. if no oil there.. try applying about 4 psi pressure with a rubber tipped air blowgun to the dipstick port... with engine running at high idle.

now. if you get oil there / had oil there.. and no lift.. you need to get a service manual and pull the lift cover ( DO back off the backpressure valve under the acorn nut PRIOR to lift cover removal.. or you will be back on looking for a 58 year old part that isn't amde anymore.. was only made for 2 years..a nd is HARD to find. ).

if you have a square vane pump.. pull the gauge out of the port on the hyd cover to look for oil.

the vane pumps were bad about wearing out.. and were upgraded to piston pumps. costs more to fix a vane pump than buy a piston pump and new plumbing conversion manifold.

 

[seanpaintsflames]

Thanks. I found that the unloader valve was stuck with an old gasket material or something. Apparently I didn't change that o-ring when I did the rebuild, but I did still have it in the kit, so it all worked out. Something that I'm really having a problem with, though, is the gasket between the lift cover and the valve body. I've had it happen three times now where the gasket blows out right where the pressure line comes up into the lift cover. I've tried the blue gasket that comes in the rebuild kit and some rubberized plasticky gray gasket material that comes in a roll. Should I just make a cork gasket or what? It gets super tiring when I get 80% done with a job that requires a lot of up and down of the lift and then it just loses pressure and can't get back up. I can get the implement off, get the top cover off and apart, and new gasket made, and back together and out in the field in under an hour now. I'd love it though, if I never have to do it again.

 

[bumperm]

Not sure what the parts look like. If the gasket in question is sealing flat surfaces, any low spot due to warping or poor machining could cause a gasket to blow out. So when you have it apart, check mating surfaces with a straight edge. An even better way is to use Dye-Kem (or a felt tip marker) on the surfaces, put some 600 grit on a surface plate (perfectly flat plate) or lacking that, plate glass is pretty flat, and rub part gently on paper to check for flatness.

bumper

 

[Cbrown9064]

Sean, not sure if your NAA is like my 861, so here goes ignorance...

On the hundred series, the pressure line and return line to/from pump go up the inside of the center section and end in the top machined area of the center section. The top cover gasket is bigger around these to hole and each gets an oring. The oring is what seals the lift cover to the lines. Is that what you are talking about?

The adapter plate and/or remote valve body also seals to the lift cover with orings.

Sorry for the ignorance if I am to understanding the NAA right. It just seems that a gasket will have a hard time holding up to that much pressure. Should be orings...

 

[Kirk-NJ]

NAA has external lines running from the pump, No internal line running through the trans case, not the same as your 861.

Kirk

 

[Soundguy]

yep.. and I think he's talking about the gasket unde rthe valve body anyway.. unless i read it wrong.

 

[seanpaintsflames]

Yes, the one under (above?) the valve body. Hopefully it's not gouged or warped- It would seem that it would be hard to do with such a thick metal part.