when we did our machine. rechroming was 700 bucks just for the chroming then parts and labour for the workshop to rekit the valves and seals. we had them both re-shafted for around 950 bucks for both and that included new seals. now thats aussie dollars. the main problem with ours was the shafts were pitted and scored so it was leaking past the gland seals. of-course without taking them apart you wont know how bad they are internally. its also possible to re-barrel the cylinders too they machine the welds out that hold the flanges to the barrel and weld a new bit of hydraulic tube in place before honing to size.

its a good idea to keep the rams covered when not in use.
what some mine sites would do was make canvas covers to keep em dry as it helped keep the abrasive dust and crap off too thus giving better wiper seal life

TOP wrote:

bluox wrote:

Inspite of all the sage advice you are getting, real troubleshooting would say repair the linkage first.
Bob
 
Already initiated this action starting with getting the service manual.
 

My local used CAT part dealer (NORCAN) was able to find two of the joints that failed. That will remove a lot of slop in the linkage. Next is tear up the floorboards and work inverted to install the thing. HAHA

neil wrote:

... #3 indicates that under certain conditions (e.g. if the rings rotate or just "seat right"), the piston seals will seal effectively. #1 indicates to me that the sealing is more effective when the pressure pushes the seals to the front side of the piston so it's possible that the piston itself might need attention....
 

I got the Serviceman's manual for all CAT hydraulics today and notice another possibility besides rings being inconveniently aligned. There are two relief valves in each  piston. It they are acting up it seem like they could cause a problem too by not seating well in one or the other direction. It also seems like the rings would have to be aligned wrong in both pistons to see what I am seeing. Any thoughts?

neil wrote:

You can get leak-by on just one piston which would enable both rams to leak down, because they're on the same circuit
 

Then the question becomes diagnosing which side. I have never torn down the hydraulic unit so I am not sure how it is plumbed or if there is a way to tell. When I change out the hydraulic fluid I'll look for any kind of junk in the oil or on the magnets. I am not sure that either rings or relief valves would be affected by the small movements of the control lever that can either put it in leak down mode or hold mode.  I am pretty sure that we are dealing with multiple issues on this old a machine with unknown maintenance history.

 

I believe your rams are the same design as the ones on my D6 9u. They are V rings and not O rings or lip seals on the piston. They tend to be more costly to buy than some other types. My rams have the chrome flacking off, but no pits from rust.They don't seem to cut the seals or leak much.

Generally it pays to start by putting new parts in the ram than worrying about pumps and valves leaking. If one ram is warmer than the other it is the one with the most oil passing the piston seals. If one side leaks internally you might as well do the other one as well..

yes do a pair. less chance of introducing contaminants and less expense with oil as your doing the job once. also it eliminates a bit of wear here and there that adds up a lot.

when we did ours we also had new bushes made for the ram eyes too. so its bronze on steel instead of steel on steel better to flog a bushing than the rod eye or pin.

I did an oil change and parked the machine for the winter. Won't get back to it till Spring now so lots of time to think about this and make arrangements.

After the oil change I ran the engine to check for leaks and oil level. I also did some more testing with cold oil. Here is what I found.

First I ran the blade fully up against the stops and then down against the stops. I did this several times to exercise the relief valves in the pistons.
Second I moved the control to the center of the hold position with the blade all the way up. It stayed put for a minute.
Third I repeated this moving the blade down a bit at a time. I could always find a position of the control that would hold the blade with no appreciable movement.
Fourth, with the blade holding at any position if I moved the control away from center so that I got just a little resistance the blade would drop. This happened whether moving the control to DOWN or HOIST. RPMs were near maximum.

Conclusion: Since the blade would hold if the control was centered manually the cylinders by themselves were not causing the blade drop. The primary cause seems to be in the centering of the spool in the valve coupled with less than stellar pump performance and probably less than stellar piston seals.

When the oil gets hot it will get to the point that the blade cannot be raised at all.

The machine is one I just got so history is unknown. What fluids are in the hydraulics is unknown also. When I get back I may drain the system and check the oil for signs of pump failure and see if fresh oil helps. After seeing that the air cleaner likely hadn't been cleaned for a long time it is likely the machine in it's recent history was not well maintained, it was just a runner.

The cylinders could definitely use a rework, but that won't solve the problem of control centering causing drop even when cold. I am not yet familiar enough with the linkage to know whether centering is something that happens inside the unit or externally in the linkage.

I found diagrams for the No. 46 system in the Service Manual. You can see that moving the spool from HOLD to HOIST could possibly dump some pump flow back into the resevoir which would cause drop instead of hoist. That would suggest a weak pump.

I probably won't get back to this thread for a bit as I have some other things that need doing. Thanks for all the ideas.