Thoughts on main hydraulic pump worn out vs individual cylinder seals bad

[1TrueSeeker]

I purchased a used 2007 3540HST 1235 hours, was told it was an ex- USFS rig. Factory FEL and BH900 backhoe. The unit runs good and operates OK, but seems a little underpowered at times. Both FEL and backhoe leakdown, even while running. I thinking the main hydraulic pump seals are bad or worn out, I can't see that every hydraulic cylinder has bad seals. How would I go about testing the main pump and the cylinders? Any idea what a new complete hydraulic pump replacement would cost? Is there a main relief valve that could be bad? Thoughts would be appreciated.

 

[FlatlandTransplant]

The pump does not supply pressure to hold the cylinders in place. The control valves hold the fluid in the cylinders which holds them in place. Same story with the relief valve, unless you are making the attachment move, it is doing nothing. A bad relief valve would cause the hydraulics to be weak.

Leaking down is likely the valve is worn. There are some YouTube videos on how to check the cylinder seals that do a better job of explaining than I can do here, check those out.

 

[North Idaho Wolfman]

Ditto to what Flat Land Transplant said!

With 1235 hours, I really can't see wear being a real issue?
But if they didn't do fluid and filter changes on time it could have had a detrimental impact on it.

If the loader lift or dump and/ or the BH is falling at a fast rate it's almost always the valve, and no they are not resealable, they would need to be replaced.

A speed of operation issue could be Valves, Cylinders, Relief valve, or Pump.
Testing is required.

 

[TheOldHokie]

I purchased a used 2007 3540HST 1235 hours, was told it was an ex- USFS rig. Factory FEL and BH900 backhoe. The unit runs good and operates OK, but seems a little underpowered at times. Both FEL and backhoe leakdown, even while running. I thinking the main hydraulic pump seals are bad or worn out, I can't see that every hydraulic cylinder has bad seals. How would I go about testing the main pump and the cylinders? Any idea what a new complete hydraulic pump replacement would cost? Is there a main relief valve that could be bad? Thoughts would be appreciated.

Bad piston seals allow cylinder drift in just one direction '- extend. If a cylinder is retracting under load it is not the piston seals. It is an external leak or internal leak in the control valve.

You test the pump with a pressure gauge. It has dothing to do with cylinder drift.

Dan

 

[1TrueSeeker]

Okay, so what I'm hearing all of you say is that the issue is in the control valves for both the FEL and the backhoe. And that the control valves cannot be rebuilt, but would have to be replaced, correct?

 

[TheOldHokie]

Okay, so what I'm hearing all of you say is that the issue is in the control valves for both the FEL and the backhoe. And that the control valves cannot be rebuilt, but would have to be replaced, correct?

That is not what I said. Before I would say that I would need a much more detailed description of exactly how the cylinders are drifting.

As regards the hoe some of the spools may have port reliefs that could be leaking and they are replaceable.

Dan

 

[1TrueSeeker]

That is not what I said. Before I would say that I would need a much more detailed description of exactly how the cylinders are drifting.

As regards the hoe some of the spools may have port reliefs that could be leaking and they are replaceable.

Dan

 

[1TrueSeeker]

With the bucket empty fully curled up, tractor running, the bucket will un-curl and lower itself to the ground over a couple of hours. A full loader of dirt and it will un-curl and drop in minutes. Tractor off, same scenarios take a bit longer, but not much.
The backhoe, parked/off will drop to the ground and un-curl the bucket in about 6-8 hours. The outriggers will drop about a third of the way, the left more that the right in the same time. Running, the drop is not as noticeable, but it does relax and does not hold a load locked in position.
If you have other questions or clarification please ask. Thanks, Doug

 

[TheOldHokie]

With the bucket empty fully curled up, tractor running, the bucket will un-curl and lower itself to the ground over a couple of hours. A full loader of dirt and it will un-curl and drop in minutes.
Tractor off, same scenarios take a bit longer, but not much.

Thats cylinder extension - very possibly bad seals in the bucket cylinder(s). You would need to test those cylinders to be sure.

The backhoe, parked/off will drop to the ground and un-curl the bucket in about 6-8 hours. The outriggers will drop about a third of the way, the left more that the right in the same time. Running, the drop is not as noticeable, but it does relax and does not hold a load locked in position.

Thats less clear but some if not all sounds like cylinder seals. That said 6-8 hours is not unreasonable. You may be expecting too much from the hoe.

Dan

 

[1TrueSeeker]

Thats cylinder extension - very possibly bad seals in the bucket cylinder(s). You would need to test those cylinders to be sure.

Thats less clear but some if not all sounds like cylinder seals. That said 6-8 hours is not unreasonable. You may be expecting too much from the hoe.

Dan

As a side note, the drop on the front loader is like the ticking on a clock, drop/hold, drop/hold, drop/hold.

I will look on YouTube for cylinder testing procedures.

Thank you for your time and knowledge everyone!

 

[TheOldHokie]

As a side note, the drop on the front loader is like the ticking on a clock, drop/hold, drop/hold, drop/hold.

I will look on YouTube for cylinder testing procedures.

Thank you for your time and knowledge everyone!

To test the bucket cylinders in the loader:

1. Start tractor, raise boom slightly and fully curl bucket.
2. Disconnect quick coupler going to base end of bucket cylinders
3. Move joystick to curl position and hold. If bucket dumps with joystick commanding curl the piston seals in bucket cylinders are leaking. If bucket remains curled seals are good.

Dan

 

[1TrueSeeker]

To test the bucket cylinders in the loader:

1. Start tractor, raise boom slightly and fully curl bucket.
2. Disconnect quick coupler going to base end of bucket cylinders
3. Move joystick to curl position and hold. If bucket dumps with joystick commanding curl the piston seals in bucket cylinders are leaking. If bucket remains curled seals are good.

Dan

Awesome, Thank you Dan

 

[TheOldHokie]

Awesome, Thank you Dan