Backhoe dipper leakdown

[MACflyer]

I have a Yanmar B65 backhoe attachment for my tractor. The dipper has started to quickly leak down if hydraulic pressure is not applied to keep it extended. With engine on or off, the rate is the same. It goes from fully extended to fully retracted in just over 3 minutes. Everything else seems to function properly, and digging force is normal. I have not found any external leaks around the cylinder. Is it likely that an internal seal is allowing fluid to bypass?

 

[Dman1981]

Start it up cold dead head cylinder on hydralics see if it gets hot where piston is
Or fully extend it pull head line and cap it see if oil keeps running out when you dead heap again if oil keeps shooting out
Don't cap cylinder just line

 

[oldnslo]

For clarification Which way is the cylinder moving when drifting? Extending or retracting?

 

[rScotty]

Here is a picture of a B26 backhoe. The dipperstick cylnder s the middle one of the three, which is the cylinder just above the Yanmar name decal.
As the dipperstick is extended, the cylinder is compressed, so as the dipperstick leaks down, the cylinder is extended....showing more of the rod. Is that correct, MACflyer?

That cylinder gets used a lot when backhoeing as you move the bucket back and forth. Usually the dipperstick motion is used to fill the bucket and to push material away. So that cylinder is usually strong enough to move the tractor around and even cause slide the stabilizer legs to skid.

Since you say that digging forces are normal, the problem may not be in the cylinder internal seal. One test you can do to confirm that is to hook the bucket teeth into something that it cannot move, and then see if trying to move the bucket with the the dipperstick will put it into relief. Most backhoes will try to move that load and then when they cannot you will hear the relief vavle cut in. If it does that, it probably means that the internal cylinder seal is OK and so is the relief valve.

That leaves the check valve. Each spool on the backhoe stool rack has a check valve. The check valve is what keeps each cylnder from moving when another cylinder is doing some work. For example, the dipperstck spool check valve holds the dipperstick up and won't let it droop when you are using the hoe as a crane.

If that check valve has a piece of crud stuck in it it needs fixing. It's not an uncommon happening for BH check and relief valves to need attenton, and on most hoes it is easy to do.

Luck,
rScotty

 

[oldnslo]

I have a Yanmar B65 backhoe attachment for my tractor. The dipper has started to quickly leak down if hydraulic pressure is not applied to keep it extended. With engine on or off, the rate is the same. It goes from fully extended to fully retracted in just over 3 minutes.

Guess need to read and comprehend the original post.

Cylinder is retracting so valve is the leak point. Would look to confirm that the spool is being returned to home position via springs. Compare height of this spool vs others in the valve bank.

If that valve section has work port relief it could be that relief leaking also.

 

[rScotty]

Guess need to read and comprehend the original post.

Cylinder is retracting so valve is the leak point. Would look to confirm that the spool is being returned to home position via springs. Compare height of this spool vs others in the valve bank.

If that valve section has work port relief it could be that relief leaking also.

I think the cylinder is extending as the dipperstick leaks down. Confusing. We need the OP to weight in here.

 

[oldnslo]

I think the cylinder is extending as the dipperstick leaks down. Confusing. We need the OP to weight in here.

Depends on what the OP thinks the dipper is..

Agree on needing clarification of which way the cylinder is moving

 

[MACflyer]

For clarification Which way is the cylinder moving when drifting? Extending or retracting?

Cylinder is extending during drift, this retracts the dipper.

 

[MACflyer]

Here is a picture of a B26 backhoe. The dipperstick cylnder s the middle one of the three, which is the cylinder just above the Yanmar name decal.
As the dipperstick is extended, the cylinder is compressed, so as the dipperstick leaks down, the cylinder is extended....showing more of the rod. Is that correct, MACflyer?

That cylinder gets used a lot when backhoeing as you move the bucket back and forth. Usually the dipperstick motion is used to fill the bucket and to push material away. So that cylinder is usually strong enough to move the tractor around and even cause slide the stabilizer legs to skid.

Since you say that digging forces are normal, the problem may not be in the cylinder internal seal. One test you can do to confirm that is to hook the bucket teeth into something that it cannot move, and then see if trying to move the bucket with the the dipperstick will put it into relief. Most backhoes will try to move that load and then when they cannot you will hear the relief vavle cut in. If it does that, it probably means that the internal cylinder seal is OK and so is the relief valve.

That leaves the check valve. Each spool on the backhoe stool rack has a check valve. The check valve is what keeps each cylnder from moving when another cylinder is doing some work. For example, the dipperstck spool check valve holds the dipperstick up and won't let it droop when you are using the hoe as a crane.

If that check valve has a piece of crud stuck in it it needs fixing. It's not an uncommon happening for BH check and relief valves to need attenton, and on most hoes it is easy to do.

Luck,
rScotty

Here is a picture of a B26 backhoe. The dipperstick cylnder s the middle one of the three, which is the cylinder just above the Yanmar name decal.
As the dipperstick is extended, the cylinder is compressed, so as the dipperstick leaks down, the cylinder is extended....showing more of the rod. Is that correct, MACflyer?

That cylinder gets used a lot when backhoeing as you move the bucket back and forth. Usually the dipperstick motion is used to fill the bucket and to push material away. So that cylinder is usually strong enough to move the tractor around and even cause slide the stabilizer legs to skid.

Since you say that digging forces are normal, the problem may not be in the cylinder internal seal. One test you can do to confirm that is to hook the bucket teeth into something that it cannot move, and then see if trying to move the bucket with the the dipperstick will put it into relief. Most backhoes will try to move that load and then when they cannot you will hear the relief vavle cut in. If it does that, it probably means that the internal cylinder seal is OK and so is the relief valve.

That leaves the check valve. Each spool on the backhoe stool rack has a check valve. The check valve is what keeps each cylnder from moving when another cylinder is doing some work. For example, the dipperstck spool check valve holds the dipperstick up and won't let it droop when you are using the hoe as a crane.

If that check valve has a piece of crud stuck in it it needs fixing. It's not an uncommon happening for BH check and relief valves to need attenton, and on most hoes it is easy to do.

Luck,
rScotty


View attachment 3727966

Yes sir this is all correct. Based on this information, it definitely sounds like the check valve is where I need to….check. Sorry I’ll see myself out.

 

[rScotty]

Yes sir this is all correct. Based on this information, it definitely sounds like the check valve is where I need to….check. Sorry I’ll see myself out.

Well, let me at least add that backhoe valves have more parts and functions than other valves. And lots more places where a bit of debris causing a valve not to close will cause a problem.
As I look back through old TBN threads for a couple of decades I think that more than a few backhoe control problems were caused by a bit of crud somewhere in the backhoe valve stack.

I didn't realize just how many valves faces and potential crud sites were involved in a backhoe control valve stack until I got the factory workshop manual for my Kubota backhoe. It was an eye-opener & took me several evenings of following their diagrams to figure it all out. But worth it.

But when I finally saw how it worked, several other things became obvious:

1. The backhoe valve stack is just a group of very similar valves bolted together, all fed at one end and with fluid returns at various places along the fluid flow path through the stack..
2. The main boom, dipper, and bucket valves are in the middle of that valve stack and are darn near identical. In fact, each one of those valves has its own relief and check valve attachment - and those ARE identical.
3. New relief and check valves can be ordered (Messicks) and I did that....though that was back some years ago before they got so expensive. I still have those parts, because before they were needed I discovered that the relief and check valves are actually easy to take off and service.
4. The manual didn't make it clear about servicing the check and relief valves. But even so, it had useful illustrations of how the relief and check valves were put together which made it easy enough to figure out how to unscrew them, clean them up, & put the back on.
4. Overall, I would have neverr figured any of this out without the workshop manual diagrams.
Luck,
rScotty