I have a 1970s 24-ton JCB 808 excavator that gets daily work. It’s a great machine for use around my farm but it has reduced hydraulic power at almost every function - it struggles to turn, the boom and dipper aren’t as strong as they should be, and it struggles to slew on sloping ground. The hydraulic pump is generating good pressure, every relief valve on the machine is activating right on original spec. The turbo Perkins 6.354 is running like a dream and never shows signs of being under powered. The hydraulic oil is new, the tank is full, it’s ISO 68, and the oil temperature stays under 55 degrees celsius. I’d like to improve the hydraulic performance as much as possible and am looking for the best places to start looking. Given pump pressure and engine horsepower are good and relief valves are operating at spec, where are the next likely sources of power loss on a machine of this type and age?
Worn out ram internals is allowing the oil to move past them is my guess. Welcome to the Forum.
Do the cylinders creep at all? Hydraulic pumps could just be getting tired. Might show good pressure in a quick test but under load the pressure and/or flow drops. What shape are the suction hoses and other hoses in? Also have filters and suction strainers (if has them) been replaced? The Perkins 6-354 is a great engine and very fuel efficient.
had a similar issue on my JD 410B after I took the dipper cylinder off to reseal it. The performance on that cylinder was really slow all of a sudden. Thought for sure I did something wrong on the seal work, and ... well it turns out I'd left a bit of that blue oil paper towel in a hydraulic line and it traveled up to the control lever. it was stuck in the valve and barely let the fluid pass. when I took apart the valve, I found more than just the paper towel, there was also some grime. so.. took my time and cleaned and replaced the orings and seals on the valves for the backhoe. it made a nice difference to clean those. of course the paper towel was the worst offense, but the rest of the valves had enough plaque on them to just need a good cleaning. Oh, yeah, I once had the return line collapse on that machine. suction caused it. I replaced the main hydraulic filter and that went away and performance was great then. that seemed to affect one direction much more than others. I know I'm talking about a backhoe, but .. it's from 83, your excavator is from the 70s... maybe it's just a filter or a suction line collapsing?
Thanks, mate. What about the slew and track drives? Will oil pass through parts of those if the internal clearances are too great?
Thanks for your reply, Dave. The boom cylinders creep and are leaking so they'll need resealing, the dipper and bucket rams don't creep and are actually pretty strong. The suction side of the circuit is good - mostly steel with small sections of hose to allow movement. The hose sections are all in good condition. I was wondering if they might be letting air in - how would I test for that? The hydraulic filters are new but I hadn't considered the suction strainer so maybe I'll check that out. I noticed today some oil leaking out of a slew spool - can a few leaky spool seals add up to some significant losses?
Mate, that paper towel trick would have done me in. I can't imagine how much time you must have spent tracking that down. Your tips re cleaning and resealing those valves are appreciated, I'll add that to my list.
Any leaks can contribute to reduced performance whether the leaks are internal or external.
It sure will, they don't last forever. To determine the leakage a simple test is to check the casedrain oil flow volume. To do this, with the bucket on the ground, remove the casedrain line off the slew motor and fit a hose that will reach a pail. then with the engine at full throttle hold the slew lever hard over in one direction and hold it there for1 min and stop. measure the amount of oil in the pail. Anything more than 5 litres is bad. Do this test with the track drive, a lump of hardwood or steel jammed in between the chain and sprocket should stall it.
I am no expert but I fixed lots of issues on my excavator. To me it seems that the pumps would be the problem since you notice weak performance on all functions. The pressure may be up to spec but pump could still be leaking internally. To examine the pumps performance the right approach would be with the flow meter but those are pretty expensive. I had a weak track that was caused by the pump. The pressure readings were okay. Still my gut was telling me pump was the issue cause dipper arm was also a bit weaker. Decided to tear down the pump and sure enough the valve plate was cracked through the kidneys. After putting it back together I did the pressure readings again and they were the same even though the pump has been rebuilt and fixed those weak functions.
That's a great tip, thanks very much. That's my weekend taken care of.
That's good advice, thank you. A six-pack of beer is probably all I need to borrow a flow meter from the local hydraulic shop....
I need to think more like a vascular surgeon and less like some guy with an old excavator....
I’d be looking into pump internal wear also. A pump can produce full pressure even if it’s down on flow. Does it run gear pumps?
A flow meter with a pressure gauge is the go to get a true story of what the pump is doing/not doing.
It does have gear pumps, yes. I don't think there's any way to test gear pumps for internal leaks without stripping them down, is that right?
Flow meter test or tear them down. The problem is once you open a gear pump up you will probably need a seal kit to put it back together. Most of the seals at that age will be brittle and break up as you pull it apart.