Backhoe problem

[rScotty]

Another reason i'm thinking about trapped air is the connections to the cylinders not on the top of it, but on the side which theoretically can trap some air above the fitting. But again, it is my theory which is most likely wrong.
there are the pictures

OK. I'm looking at that picture. The side port trapped air theory didn't pan out IMHO, because some research shows that to be a common way to port swing cylinders.

But while I was looking at the photo you posted and thinking what else could be going on with that cylinder I realized I can't see how that cylinder would be rebuilt. How does the end come off? Could they be non-rebuildable swing cylinders?
Is there even such a thing as non-rebuildable swing cylinders?
rScotty

 

[2515R Dude]

Here are better vids.

 

[ning]

Looks like there's a lot of play with that cylinder - the main body of it is moving in and out as the boom swings to the right. I wonder if there's so much slop with possibly both of them moving that it only looks like things are stopping but the cylinders are still extending & retracting correctly, it's just that when it's "catching up" to the slop that the entire unit appears to stop.

idk if you can get someone to watch the back of the swing cylinders, look for the whole thing moving back and forth, then check the pivot point and see why it's so loose.

 

[ericm979]

Watching the end of the cylinder, it's not moving back and forth when the boom stops swinging momentarily. I think the rod is speeding up and slowing down. The rod end play makes the swing appear to stop and start as the cylinder slows down and intertia throws the boom against the other end of the rod play and then it sits there until the rod catches up and takes up the play and starts it moving.

My BH760 has some play there too, but it moves evenly until I stop the motion via the joystick, then it wiggles a little. Something's wrong with yours.

As to why the cylinder speeds up and slows down, I dunno. Maybe you could lock the boom with the travel lock and unbolt the rod ends of the two cylinders, then operate them while watching. If the places where the swing stops changes and another motion using different cylinders also shows the problem, its unlikely to be damaged cylinders or pivot points.

Does it still move unevenly when you have the rpms up? How about when the bucket is in dirt instead of air?

 

[JRP3]

How does the end come off?

There is probably a hole or notch where you can't see it.

 

[LD1]

I think its a little bit of air in combination of the hydraulics trying to decide if it wants to push with the one cylinder or pull with the other. I think the slight slop in the pins, in combination of the cylinders trying to decide back and forth which one has the least resistance to operate, and that is the problem you are seeing.

Also sounded like it was at/near idle. What does it do if its at PTO RPM?

Also, what does the boom do that you said you were also having issues with

 

[rScotty]

Wow. Good Videos. That is a lot of unnecessary mechanical movement. Way more than normal for a BH. The swing system is normally much tighter. Here we've been looking at the hydraulics and it may be that the mechanicals need attention first. There is enough movement to make me wonder if one or both of the swing cylinder mounting bushings is missing. It could also be enough play that the slop is what you are seeing and not some sort of air cushion effect at the end of the swing.

I'd replace the bushings in the swing system pivots first. Or make yourself some new ones. And while you have the cylinder out, either disassemble the cylinder or somehow check that the rod is firmly attached to the piston - i.e. zero end play.

Once you get the mechanical slop minimized the hydraulics may make more sense.

rScotty

 

[Rich B1]

Hydraulics work best with the engine at full RPM. Or at some specified RPM in the operator manual. It may be at low RPM, there is insufficient flow to swing the boom correctly. Odd hydraulic issues at idle are, IMO, no surprise.

Do your test again at the specified RPM in the operator’s manual. Also test it under a load at the specified RPM. what happens?

 

[rScotty]

Hydraulics work best with the engine at full RPM. Or at some specified RPM in the operator manual. It may be at low RPM, there is insufficient flow to swing the boom correctly. Odd hydraulic issues at idle are, IMO, no surprise.

Do your test again at the specified RPM in the operator’s manual. Also test it under a load at the specified RPM. what happens?

Sure it does, but don't you think that hydraulic flow should depends on the implement? Sometimes we don't want max flow. Backhoes have long mechanical arms that need to be precisely moved by fairly small hydraulic cylinder movements. It is common for backhoe work operators to work at idle instead of full RPM. Full RPM makes a backhoes jerky and fast enough to be slamming around. Kinda dangerous.

For snow blowers, water pumps, mowing, and tillers testing at full RPM makes sense. For a backhoe I'd learn more at low RPM than at high.

rScotty

 

[ericm979]

For me and my Branson and backhoe, about 1800-2000 rpm is right. PTO rpm is 2500. When it's too low it gets slow when you open more than one valve at the same time. At full PTO rpm it's a little too fast for me.

But I think people are asking for the OP to try higher rpm to see if it behaves differently.