Improving Hydraulic Performance

[CountFred]

Forgive my ignorance of all things hydraulic, I've been searching around but don't seem to know what keywords I need to find the right information.

I have a John Deere 4500 with a 460 loader.

The specs on the loader indicate: Lift to full height (at 800mm): 2,325 lbs

However, I am unable to life a 1-ton (2000lbs) pallet out of the bed of a truck. I can take enough weight off that I can slide it out, and hold it at height. That seems well less than "full-height" and with the lift spec at 800mm, a 4' pallet should have a center of gravity inside of that.

I can lift that much weight a few inches off the ground, but that's about it. From the spec it seems like I should be able to do better. Is it possible, given the age of this tractor, that it can no longer lift what it once did? Would it possible to "tune-up" the system to get it back to original spec performance? Are there some obvious troubleshooting steps to help with this?

This is all done with a JD 48 backhoe on the back, so that should be plenty of weight to keep the tractor from unloading the rear as I try to load the front.

Thanks for your thoughts!

 

[CountFred]

I should add, that I have recently replaced the hydraulic fluid and filters with JD recommendations. Although it had no effect on performance, it was time to do it.

 

[RickB]

Check the system relief pressure.

 

[oldnslo]

My suggestion would be to purchase a pressure gauge and required fittings so that you can to see if you can achieve the specified pressure for your tractor. If it does not meet spec then you can start looking for the cause.

 

[CountFred]

I see that KBOGH makes a pressure tester, so I think that's first on my list now. Manual lists the working pressure as 2500 psi. I assume that is the pressure at which the relief kicks in and what I should expect to be seeing on the gauge.

 

[Wagtail]

Quick question; what attachment/configuration are you using to lift the pallet with your FEL?

A bucket with 'bolt on' forks? Dedicated pallet forks utilising a Skid Steer Quick Attach (SSQA)? Dedicated pallet forks utilising a JDQA?

 

[CountFred]

Dedicated pallet forks utilising a JDQA

 

[oldnslo]

Yes that would be the pressure you should see. I suspect there is also a tolerance range.

In hydraulics pressure is the lifting force on an FEL while flow dictates the speed or velocity

 

[Tractor Seabee]

The tractor specs are usually at the attachment pins of the FEL. Forks attached to the bucket move the center of gravity forward the width of the bucket which decreases that type lifting capacity. Simple physics. I do not know the math involved. I had the same situation with my BX. I check the HYD pressure; it was below spec of 1700+PSI. I shimmed the relief valve to increase to 2000 PSI. That helped a lot but did not meet the loss.

A fork unit attached to the bucket pins will restore a lot of loss that just a 4' pallet will create also due to the center of gravity of the pallet itself. When I can i concentrate the pallet load as close to the tractor as possible. Example; if you load concrete blocks on a pallet and stack two high you can lift a certain weight, move that weight back to 4 or 5 five high you can lift a whole lot more.

Ron

 

[IceStationZebra]

Actually loaders are rated to the center of the bucket mass, bucket rolled to get max fill. I used to work for an OEM and had to test several machines. They may also be using the lightest bucket option to get the biggest advertising number - for instance you may have a bolt-on cutting edge that is optional.

Curious, did they state capacity at height just like you stated, or did they state lift height and capacity seperately? Sometimes people see them seperately but assume it is capacity at height.

Also realize that just because you can lift a load does not necessarily make it safe. Make sure you have sufficient stability based on you work surface and slopes.

And one little trick you might try - on many machines the tilt cylinders have more lift capacity than the hoist/arm cylinders to make up for the poor geometry. Try tilting the forks down slightly, then raise the load as much as you can with the hoist cylinders, and finally tilt back. Sometimes this will give you the just enough lift to move a load.

ISZ

 

[RickB]

Actually loaders are rated to the center of the bucket mass, bucket rolled to get max fill. I used to work for an OEM and had to test several machines. They may also be using the lightest bucket option to get the biggest advertising number - for instance you may have a bolt-on cutting edge that is optional.

Curious, did they state capacity at height just like you stated, or did they state lift height and capacity seperately? Sometimes people see them seperately but assume it is capacity at height.

Also realize that just because you can lift a load does not necessarily make it safe. Make sure you have sufficient stability based on you work surface and slopes.

And one little trick you might try - on many machines the tilt cylinders have more lift capacity than the hoist/arm cylinders to make up for the poor geometry. Try tilting the forks down slightly, then raise the load as much as you can with the hoist cylinders, and finally tilt back. Sometimes this will give you the just enough lift to move a load.

ISZ

Loaders are rated at the specified location. Typically at the pins or a specified distance ahead of the pins. Some ratings specs follow industry standards, some do not.

 

[CountFred]

And by pins do they mean the bucket pins? Or the main pin around which the main cylinder causes rotation?

Also when loads are specified at full height, does that mean it can move that amount from 1" below full height to full height, or can move that amount all the way up and to full height?

I can usually muddle through the free body diagram and simple physics but don't always know how the terminology is used on tractors.

 

[CountFred]

Having now acquired a way to measure the pressure, it jumps nicely to 2600 and then bleeds down from there. That is a touch higher than I expected, although I don't know if that is significant.

Anyone have suggestions on other things to check?

 

[PILOON]

Bleeding down suggests to me that you have leakage and I'd suspect in the lift valve.
Obtaining that high pressure, to me, indicates the pump is performing properly with loss further down line.
One thing it could be is some debris in or around the pressure relief valve which is probably part of the valve block and that can be dismantled to check.
Would not take much more than a grain of sand (or similar) to allow pressure to bleed off.
On most valve blocks that I am familiar with the pressure valve is under a screw on cap that is part of the valve assembly.
Try googling your valve block part no and brand for more info.

 

[CountFred]

Sorry, I should have been more clear. It only bleeds down when I release the control lever.

1. Apply lever - pressure jumps to 2600 and stays there as long as the lever is pressed
2. Release lever - pressure will drop down to 0psi slowly (maybe a minute to get all the way to 0)
3. Apply reverse level - pressure will drop to 0psi immediately

Are you saying that I should not be seeing a drop in step 2 there?

If so I'll go look at what I can take apart with the pressure relief valve and clean. Given the life of this tractor before I got it (and my inexperience since having it) it would not surprise me if there was some particulate that got in to the system and could be blocking a valve.

Would that affect my overall lift capacity however? If the pump is able to continue to apply 2600psi I would expect it should have full strength to lift. (This being my original symptom)

 

[IceStationZebra]

Loaders are rated at the specified location. Typically at the pins or a specified distance ahead of the pins. Some ratings specs follow industry standards, some do not.

I looked at a couple Kobutas and was surprised to see you are right. I can only assume this is done so marketing can publish the largest number while the average consumer is not aware of what is really going on. Every OEM will have a different distance between the bucket CG and pivot pins, but I suppose they all end up in the same neighborhood so they will be comparable plus/minus a couple hundred pounds.

Ag tractors do a similar thing with 3-pt lifting capacity. To get the lift numbers they publish you need to add a LOT of additional weight on the front of the tractor and excludes tire squat. I have seen it where a nearly bare chassis was bolted to the ground and lifted against a load cell in a pit. Similarly track loaders are tested with the front idlers at max forward position. Not to mention that every tractor tested by the Nebraska Tractor Test is hand tuned by the OEM before the university gets it. Could go on for a while.

ISZ