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.

 

[J_J]

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--

I believe you left out one important consideration, and that is there are external forces, working to apply pressure to the cyl, therefore acting as a manual pump, pushing fluid to the other side of the piston. The weight of the boom and bucket are trying to extend the cyl by weight alone.

I also believe that most people in this situation, are changing out the piston seals, less expense for one thing, and correcting the problems than they are replacing their control valves.

They both can be checked using a manual hyd pump.

 

[ditech]

Hi Guys,

The information I posted earlier was purely from memory (we can all probably relate to that ) anyway, the basis for my opinion is still true. Check out the link below Troubleshooting hydraulic cylinder drift
It's interesting reading and may shed some light on what I was trying to relay. I know I don't post a lot, but I do get a lot of good insight, opinions and advice that I can apply to my tractor. Hopefully, occasionally I can add something of value to the forum. I appreciate all of the "regular" contributors and respect their views. When I offer an opinion that is against the grain I will try and back it up with reliable data, info or from a looooong time in the heavy diesel trucking industry

Ditech

 

[TruChaos]

Thanks for all the information. There is one thing I should have added. When the backhoe was first installed, it had a problem. When the fluid would heat up, the hoe lost all of its ability to do work. The boom would barely lift, etc. So I increased the viscosity of the hydraulic fluid and that solved the problem. The boom didn't sag and there were no other apparent problems. Then about a year or so later the boom began to sag.

There is one behavior/symptom which I'm not sure is normal or not. When the bucket is in contact with the ground digging and I apply downward boom force, there is a one or two second delay between giving the control command and the boom actually applying the downward force.

I push the down control lever the boom will move down and makes contact with the earth, wait one, two.. then the boom pushes down and the rear of the tractor lifts slightly. I'm not sure if this is normal or not.

 

[J_J]

No , not normal unless there is some loose pins , etc, Sounds like air in the cyl. Air will take time to compress up to the hyd pressure necessary to move the cyl, whereas the hyd fluid will start to move things instantly.

 

[Bob Rooks]

Hi Guys,

The information I posted earlier was purely from memory (we can all probably relate to that ) anyway, the basis for my opinion is still true. Check out the link below Troubleshooting hydraulic cylinder drift
It's interesting reading and may shed some light on what I was trying to relay. I know I don't post a lot, but I do get a lot of good insight, opinions and advice that I can apply to my tractor. Hopefully, occasionally I can add something of value to the forum. I appreciate all of the "regular" contributors and respect their views. When I offer an opinion that is against the grain I will try and back it up with reliable data, info or from a looooong time in the heavy diesel trucking industry

Ditech

I enjoyed that well done presentation on debunking the myth of creeping hydraulic cylinders (cool software). Maybe I missed it but I didn't observe his mention of of a couple of tons of static force being applied to the cylinder while it was in "locked" state, which is the back hoe scenario. I'll view it two more times.

 

[Bob Rooks]

There is one thing I should have added. When the backhoe was first installed, it had a problem. When the fluid would heat up, the hoe lost all of its ability to do work.
What were you using for hydraulic oil in the beginning?

The boom would barely lift, etc. So I increased the viscosity of the hydraulic fluid and that solved the problem. The boom didn't sag and there were no other apparent problems.
What did you do to "increase the viscosity?

Then about a year or so later the boom began to sag.
Yes.

There is one behavior/symptom which I'm not sure is normal or not.
When the bucket is in contact with the ground digging and I apply downward boom force, there is a one or two second delay between giving the control command and the boom actually applying the downward force.

I push the down control lever the boom will move down and makes contact with the earth, wait one, two.. then the boom pushes down and the rear of the tractor lifts slightly. I'm not sure if this is normal or not.
It may be that the return oil from the cylinder is slightly restricted, and that must be overcome before the cylinder will move (how is the return line filter?), or as JJ said, there could be air in the system.

12345

 

[TruChaos]

12345

I changed the hydraulic fluid from ISO 32 to ISO 68. When I switched from 32 to 68 the filter was clear with no debris. I haven't checked the filter since.


By the way, I've often wondered, what's the major difference between hydraulic oil and engine oil. Obviously the engine oil has more additives, but can it be used in place of hydraulic fluid? Hydraulic oils can be hard to find and aren't that much less expensive than engine oil when bought by the bucket.

 

[Bob Rooks]

I changed the hydraulic fluid from ISO 32 to ISO 68. When I switched from 32 to 68 the filter was clear with no debris. I haven't checked the filter since.
Are you in the tropics or down by the equator? Does the oil say "ISO AW 68 Hydraulic Oil or something else?

By the way, I've often wondered, what's the major difference between hydraulic oil and engine oil.
A lot!

Obviously the engine oil has more additives,
Actually hydraulic oil has more additives than you think. Most are blended from paraffinic base stocks and will have additive packages that include anti-foaming and ant-wear agents, and moisture dispersants not found in engine oils. And conversely, engine oils contain additives that are undesirable in hydraulic service. People make entire careers from lubrication so I'm not going to go into any depth on the subject. But just common sense will tell you: engine oil for engines and hydraulic oil for hydraulics.

but can it be used in place of hydraulic fluid?
Yes, in special applications where it is indicated. Otherwise no, not by knowledgeable people.

Hydraulic oils can be hard to find and aren't that much less expensive than engine oil when bought by the bucket.
It is as close as the nearest auto parts store, NAPA dealer, or petroleum distributor.

12345

 

[TruChaos]

Actually the bucket said AW68 not ISO, yes it said hydraulic fluid. No I don't live near the equator. I started with AW 32 and the backhoe had no power, barely enough to lift the boom up into the upright position. Several other owners stated they had solved the same problem by going to a more heavy weight fluid. AW68 fixed that problem.

HOWEVER, today the original problem is now back. Last time I used the backhoe it worked fine but after a while the boom would lower on it's own. Now none of the backhoe hydraulics have enough power to do anything including lifting the rear of the tractor with the outriggers.

I checked the fluid level and it's normal. I unscrewed the filler cap and the cap was covered in water. It was dripping.

Awhile back I bought a spare unused hydraulic pump at a good price so I'm going to swap it out to see if that improves things. Before I do that I'm also going to drain the fluid and check the in tank strainer.

When I move the control lever the outrigger will suddenly move normally for a fraction of a second then move very slowly with no power. Almost like there is an obstruction.

 

[Bob Rooks]

Well now it sounds like you have debris in your relief valve, notwithstanding a possible blown pump. Is the new pump rated about 7 gpm? It's entirely possible that you have multiple issues, one masking the other.