New Holland TC55DA 3 pt hitch settling

[ah724tractor]

My TC55DA 3pt hitch settles under a heavy load. I first noticed this a couple years ago, but it was so slight I didn't worry about it. Gradually, the condition worsened until it now cycles the lift position valve every few seconds while running. I thought maybe the link connecting the rock shaft to the spool lever was out of adjustment, so just to experiment, I removed the link in the hopes that I could manually find a sweet spot in the spool where the hitch did not settle. I was not successful.

My backblade weighs roughly 1500 lb, and I work it hard. It's my notion that running over bumps all day with it raised has hammered the relief valve open enough that it no longer seals. And it seems worse once the oil is hot. With continued bleeding, the position link opens the lift spool which resets it, but it takes only a few seconds to repeat this cycle.

Any thoughts on where to start? Or where/how to access the pressure relief, the spool, etc? Just a week or two ago, I noticed the hitch stayed up all night, so I don't think it's a problem with the lift cylinder or piston. Service manuals are $$.

Thanks,

Kent

 

[Jerry/MT]

My TC55DA 3pt hitch settles under a heavy load. I first noticed this a couple years ago, but it was so slight I didn't worry about it. Gradually, the condition worsened until it now cycles the lift position valve every few seconds while running. I thought maybe the link connecting the rock shaft to the spool lever was out of adjustment, so just to experiment, I removed the link in the hopes that I could manually find a sweet spot in the spool where the hitch did not settle. I was not successful.

My backblade weighs roughly 1500 lb, and I work it hard. It's my notion that running over bumps all day with it raised has hammered the relief valve open enough that it no longer seals. And it seems worse once the oil is hot. With continued bleeding, the position link opens the lift spool which resets it, but it takes only a few seconds to repeat this cycle.

Any thoughts on where to start? Or where/how to access the pressure relief, the spool, etc? Just a week or two ago, I noticed the hitch stayed up all night, so I don't think it's a problem with the lift cylinder or piston. Service manuals are $$.

Thanks,




Kent

You'll have more leakage when the oil is hot versus cold because the viscosity(resisitance to flow) of the oil is higher when the oil is cold and gets lower as the oil warms up.

Since your hitch stayed up over night, whatever leakage you have in the piston/cylider and the releif valve is minimal WHEN THE SYSTEM IS ONLY PRESSURIZD BY A WEIGHT ON THE HITCH.
When you are working, if you are on bumpy ground and the hitch is up with a 1500 lb blade on it, the inertia of the blade due to bouncing can cause the releif valve to unseat in response to the pressure spike in the lift cylinder. If you are in position control, the control would then reset the position.

If you are just sitting there and the control is resetting the position, then you have a leak somewhere when the pump is operating, and that's the source of the problem.

 

[ah724tractor]

Thx. I'm clear on the fact there is internal leakage, but I don't want to tear the tractor apart looking for it. Hoping someone might know how to access the pressure relief or spool valves with minimal tear down. Those seem like logical starting points.

Kent

 

[Jerry/MT]

Have you looked at the parts drawings on the New Holland website? That's a good starting point to find the relief valve location and to get an idea what the valving looks like, though that maybe internal to the control body. That's where I'd start.

 

[jinman]

Thx. I'm clear on the fact there is internal leakage, but I don't want to tear the tractor apart looking for it. Hoping someone might know how to access the pressure relief or spool valves with minimal tear down. Those seem like logical starting points.

Kent

Kent, the pressure relief is only active while the 3PH is moving. Once the open center system goes back to neutral, the pressure relief is fully closed all the time no matter how much your lift bounces or what weight is on it. The 3PH lift cylinder does have a high pressure relief to protect it from sudden extreme loads like something falling on the hitch that might weigh around 4000 lb. I don't think a 1500 lb blade could cause any problems with that. For a quick and dirty test, raise your heavy implement all the way to the top and turn your drop speed adjustment completely clockwise. After closing this valve, turn off the engine and monitor for 3PH drop. The drop speed valve closed completely blocks all normal flow from the lift cylinder and should hold it in place as long as the 3PH lift cylinder or a checkvalve don't leak. This is a quick test to check the condition of your lift cylinder seals.