New holland tn55 lost hydraulic pressure

Kregan87 · Mar 26, 2018

I have a 270tl fel on my tn55 and has been real powerful until this past December. The loader started to be really slow and weak. Mostly on the lift pistons but a lacking a little on the curl also. I figured it was real cold hydraulic fluid but warmer temps haven't helped.

So far I have check my hydraulic pressures at various locations and at wide open throttle I am only getting 1000psi. Can even pick up a bucket of snow. Last year I was picking up massive buckets of sand and stumps with ease. I'm not sure exactly what pressures should be but the relief is supposedly set at 3000psi. So I figured I should probably be getting about 2600-2700?

I've changed hydraulic filter without any luck also. Any one have any ideas? at this point I'm thinking the pump is shot. Please any help will go a long way. I check pressures out on both sides of lift pistons, curl pistons and both sides of the loader control valve. All pressure max out just under 1000psi.

Kregan87 · Mar 26, 2018

I had originally thought the piston seals in the lift cylinders were leaking by because the lift seemed to be the only problem before I tested pressures. But once I tested pressures I noticed it was the same everywhere and figured maybe the curl pistons just don't need that much pressure to be powerful

bigdeano · Mar 26, 2018

Could possibly be something wrong with the pressure relief valve too. Did the problem start suddenly or gradually?

Kregan87 · Mar 26, 2018

I would say it was pretty sudden. Could be the relief valve but I at idle I'm getting 500psi. I feel like it should be higher at idle. Then I get up to 1000psi at full throttle. So it could be that but I do feel like if it was then the pressure should at be 1000 at idle then not increase as I go to full throttle. I'm not sure if I'm explaining myself correctly or not.

Kregan87 · Mar 29, 2018

Any ideas?

bigdeano · Mar 29, 2018

If the relief was being held partially open it would act like it's doing. Might be worth taking the relief valve apart before buying a new pump. Seems strange that a pump could fail suddenly like that. They usually just gradually wear.

Dave M7040 · Mar 29, 2018

Make certain you don't have a valve like a rear remote not fully returned to its center position. Often this is the case when you have some hydraulic operation just slow or weak.

Fluid is being allowed to return to the transmission reservoir before doing any work.

On some tractors where the rear remotes are operated by a lever and cable in the cab, disconnect the cable at the rear remote end and get it centered then try with the cable disconnected.

Of course, if you have been changing or moving hoses, a hose in the wrong place can cause a world of grief.

Dave M7040

oldnslo · Mar 29, 2018

Kregan
Is the relief valve on your machine externally adjustable or the style that requires shins? If externally adjustable try lowering the setting to the minimum and intentionally force full flow through it a few times like trying to curl fully. This might allow any contaminates to be dislodged.

Now try adjusting the relief to increase pressure to see how it responds.

Pressure should increase steadily while you making this adjustment.

Kregan87 · Mar 31, 2018

So I was trying to avoid the relief valve cause of its location on the filter housing it's blocked by the brackets for the fel. Had some times today to pull the loader off and bracket. I took the reliefs valve right out and apart. Instead of a spring it had a series of concave washers that produce tension. All looks well inside so I reassembled everything hooked up a gauge and pressure was back. Set the pressure to 2700psi and everything is perfect now.
It all started after a few weeks of really cold temps. Can't figure out what caused it but assuming the adjustment screw backed out somehow. There's no lock nut on the adjustment screw unlike a lot of other relief valves.