7308 loader won't hold curl

[john_bud]

If the cylinder packings are at fault, there will be hydraulic fluid dripping on the ground where they are leaking. The rod displacement needs to go somewhere. If it can't get back to tank, the bucket is not going to droop.
If there is no external leakage, the leakage must be internal, and MUST return to tank to allow bucket droop. Fluid just passing the cylinder piston won't do it.
Very easy diagnosis.

It is possible that the spool valve leaks between bucket and lift arm cylinders, with the bucket drooping as the arms lift. But the fix is the same. The DCV needs attention.

Your point is incorrect. Actually, the majority of cylinder leaks are internal where the cylinder packing leaks allowing the fluid to go AROUND the piston. Then the piston moves and the bucket (or boom) will droop.


No external leak and no return to the tank needed.



For the OP, the packing is both inexpensive and relatively easy to replace. But it does take large tools and high torque force.

 

[CalG]

Your point is incorrect. Actually, the majority of cylinder leaks are internal where the cylinder packing leaks allowing the fluid to go AROUND the piston. Then the piston moves and the bucket (or boom) will droop.


No external leak and no return to the tank needed.

John

In the case of your description, What happens to the fluid displaced by the advancing rod?

In normal operation, that volume/area is enough to operate the bucket action to full capacity. In fact, the filling fluid must PUSH the fluid out from the far side of the piston in order to do any useful work.

Seems odd that all the sudden, "leaking" around the piston will work counter to a good design.

Could you clarify this point? "The case of the missing volume".....

Perhaps it is only the expansion of some soft flex lines that allow things to "settle"....but I don't believe so.

The math has been done on this topic. I suggest you search the forum.

 

[Tx Jim]

If the cylinder packings are at fault, there will be hydraulic fluid dripping on the ground where they are leaking. The rod displacement needs to go somewhere.

Piston packing can leak internally allowing cyl rod & piston to move without one drop of oil leaking externally.

 

[Tx Jim]

JohnIn the case of your description, What happens to the fluid displaced by the advancing rod?

CalG
On most loader bucket cylinders I've seen the rod must come out of the cylinder for bucket to curl therefore there's no extra fluid that requires displacing IE there's less fluid on rod side of piston.

 

[brain55]

CalG
On most loader bucket cylinders I've seen the rod must come out of the cylinder for bucket to curl therefore there's no extra fluid that requires displacing IE there's less fluid on rod side of piston.

Exactly

 

[larpai]

Thanks for the help.
From what I read either the DCV or the cylinders can be at fault. The DCV in neutral should isolate the fluid in both sides of the cylinder thus locking the piston firmly. This would take several seals in the DCV leaking to cause drift, but one leaking piston seal in either cylinder would cause drift. I think I'll go with rebuilding the cylinders first.

 

[Tx Jim]

larpai
If valve is at fault the only thing that will allow a hyd cylinder to creep on a spool valve is excessive clearance between spool & housing which requires complete valve replacement IE no type of seal replacement will correct the problem.

 

[larpai]

Would switching the curl and lift lines be a way of isolating the issue?? I don't want to open up 2 good cylinders then replace the DCV. I'd like to get it right the first time.

 

[brain55]

This is how I would check the bucket cylinders. I would curl the bucket back while it is on the ground. Block the front edge of the bucket up so it doesn't uncurl when you disconnect the hoses from the base side of th he cylinders. I then plug the hoses and leave the base ports on the cylinders open. Then with the machine running I move the control to curl. If fluid comes out of either of the cylinder base ports then you know the piston seal is bad in that cylinder.

Brian

 

[CalG]

Try it the other way and see if the bucket settles "UP". For sure if the ram volume is to be considered, It will show there.

You should be able to use the tractor as it's own weight by lifting the front wheels with the bucket extension.

Best would be if you could monitor pressure on the lines. But equipment gets pricey.

True, that if Wear is the issue in a DCV, replacement is the best (only) solution. but if there is a positioning hang up, that can be rectified.

Here is an informative piece
The Root Cause of Hydraulic Cylinder Drift