YW-6 Backhoe Problem

[TruChaos]

My YW-6 backhoe has a problem where the main boom slumps pretty quickly when not in use. Everything works well otherwise. If I don't put the turnbuckles on the main boom to hold it in the up position, in a few minutes the boom slumps and bucket ends up dragging on the ground behind the tractor.

If I reach back and pull the up lever it pops back up into place without complaint.

Any suggestions?

Thanks.

 

[Rich Waugh]

Yeah, it sounds as though you need to replace the seals in the main boom cylinder. They are probably a bit worn and are bypassing fluid, allownig it to drop. When you hit the control, it pumps fresh fluid into the lift chamber and corrects the situation.

 

[erj]

My JW03 was always dropping like you stated. Since it worked OK otherwise, I decided that whenever I moved the tractor I always had the Boom pin and a chain on the bucket so they wouldn't drop.
RonJ

 

[Brad_Blazer]

It could be the valve or the cylinder.

 

[Bob Rooks]

I'll go with the piston seals because that's how mine acted until one day it didn't work at all - while I was doing a job for a customer.

 

[greyfoxxca]

Ever since I bought mine it has dropped quite quickly. It digs well and has lots of power. So I use a pin when not in use.

George

 

[J_J]

Maybe some of you don't realize this, but a loss of 500 psi will reduce the force by 1575 lbs on a 2 in cyl with 1 in shaft. . If you are losing that pressure through the piston seals, the hoe will still work, but will probably not activate the relief valve

500 psi loss on a 3 in cyl , 1.5 in rod, = 3535 lbs.

If the boom is leaking down, you are losing potential force .

 

[ditech]

Hi Guys,

Actually leaking piston seals (on a single ended, double acting cylinder) wont cause a cylinder to drift. The volume of oil contained in the cylinder increases as the cylinder extends and decreases as the cylinder retracts. This is caused by the area in the cylinder occupied by the piston rod. If your control valve (or some other source outside the cylinder) is not leaking, there is no way for the volume of oil in the cylinder to change and essentially locking the cylinder in one position. So for your boom to be drifting down, there has to be something outside of the cylinder (usually the control valve) allowing the volume of oil in the cylinder to change. Thus causing the cylinder to change position.
This does not apply to a double ended cylinder where the volume of oil contained in the cylinder is the same no matter what state of extension/retraction the cylinder is at.

Ditech--

 

[RonMar]

I guess a way to check this would be to support the boom to hold the weight, remove a boom up hose at the valve and install a blockoff disc in the ORFS fitting. Wrench it back down and then remove the support and see if the boom continues to leak down.

I tend to think it is machine tollerances in the valve body as mine does it also, faster when the fluid is warm. Piston seals usually don't leak for long. All the ones I have seen that did, failed completely not long after they started bypassing fluid around the piston...

 

[Bob Rooks]

The volume of oil contained in the cylinder increases as the cylinder extends and decreases as the cylinder retracts. This is caused by the area in the cylinder occupied by the piston rod. If your control valve (or some other source outside the cylinder) is not leaking, there is no way for the volume of oil in the cylinder to change and essentially locking the cylinder in one position. So for your boom to be drifting down, there has to be something outside of the cylinder (usually the control valve) allowing the volume of oil in the cylinder to change. Thus causing the cylinder to change position.
This does not apply to a double ended cylinder where the volume of oil contained in the cylinder is the same no matter what state of extension/retraction the cylinder is at.

In my exhibit the volume of oil does not change. True. However, the sheer weight of the boom will allow (force) oil to pass from one side of the piston to the other, around the defective seals. No oil leaves the cylinder (Pascal's Law).

The OEM Chinese cup seals literally disintegrated in my case plugging the system, however the replacement seals were polyurethane and held up well.

Easy way to test the theory: Fully extend the boom, jib, and bucket and raise to full height. Turn off the engine and note the level in the hydraulic reservoir. Wait a few hours or overnight and check the position of the boom and jib. Check the oil level in the reservoir to see if it has risen. If boom and/or jib have dropped with an increased oil level then the issue is in the valve stack, if only the boom dropped with no increased oil level then the issue is in the boom cylinder.