Go BottomCylinder Drift on Bradco Backhoes
 | marty1
Join Date: Oct 2003 Posts: 4 
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2003-11-18 69059
Hello all, here is my story...
I have a 2003 B7800 with a Kubota FEL and Bradco 3375 Backhoe (7' reach). Dealer said this backhoe was a little more powerful than the comparable Kubota model, and used a subframe for added support and strength. Fine, I'm using it to put in 2000' of retaining wall on a fairly steep hill. I just turned 100 hrs on the tractor with about 40-50 of that using the backhoe. All fluid changes etc. followed religiously. Love the backhoe it's a real monster, and for a while things were great. However after about 20 hrs, on it I noticed that if I did not pin it up at night, by morning the bucket would be on the ground. Took it back to the dealer who said that some drift is normal but not that much, so he replaced the cylinder. He also said that the new Bradcoe cylinders use a different seal structure (not the leather type) that is supposed to be more efficient and some drift is to be expected. When I got it home and tried it out again I found the probem was better than when I took it in, but still there. If I drive I drifve around for 10-15 minutes, The backhoe will drop an inch or two. In fact, I've also noticed now if I park it on a hill at night, by morning the bucket will be swung almost completely to one side. Is this common in backhoes (bradcoes especially), and would I see this had I bought the Kubota backhoe instead? Also, does drift impact the overall performance of a cylinder while under load? (PS, I have 60 hours of hard work on the bucket, and it does not sag at all...)
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 | DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada 
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2003-11-18 69064
I have only a few hours on my new deere 46 B/H and it does pretty much the same thing, even when it is not connected to the tractor.
The FEL drifts too..............
Unless.....
It is cold outside, as in 40 degrees or less, then it stays put for days instead of hours.
I think the name of the game is oil viscosity.
....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-11-19 69073
Leak-down isn't much of an issue unless it's enough to be irritating when using the hoe. It won't affect the hoe's power as long as the relief valve can be opened when a cylinder is on its stops. Leaks might slow it down slightly. ....
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| lamarbur
Join Date: Jul 2003 Posts: 93 Ma/Ct state area
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2003-11-19 69080
I have a Bradco 511, the bucket will curl after a few days and if I forget to pin the hoe back, it too, will dropp down to the ground in a few days. You have to remeber that these are not commercial hoes like the JD 710 I run on occasion now where they lock in place ....
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| marty1
Join Date: Oct 2003 Posts: 4
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2003-11-19 69111
Good, I know some drift is inevitable through usage, but wanted to make sure what I was seeing was not necessarily out of the ordinary. Still curious if anyone has Kubota Backhoe and what their experience has been with this....
....
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| imtools
Join Date: Nov 2003 Posts: 34 Ridge, NY
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2003-11-20 69152
I don't have any experience with a backhoe but as a mechanical engineer and somewhat familiar with hydraulics, I can say that the movement can be caused by fluid bypassing the piston seal in the cylinder OR bypassing the port in the valve. Most (if not all) of the valves used are spool type and there aren't ANY seals between port-just a very close fit. Seepage under pressure is inevitable.
By the way, if the leakage is across the cylinder and the rod is retracting, it almost certainly valve leakage. The reason I say this is because as the piston moves in, it displaces more volume on the non-rod side than on the rod side. If it leaks past the piston from the non-rod side to the rod side, it is fighting increased pressure. I hope I expalained this without confusion.
Paul ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-11-20 69164
Always good to have more ME perspective around here. Confusion is my friend because confusion always precedes learning.
I'm thinking about your aside. The way I'd think of it is that at rest the spooling valves block the work ports and most leakage there would go through the valve assembly to the return line, although I suppose it's possible to get from work port to work port across the valve assembly.
The cylinder o-rings block oil going from one side of the cylinder to the other. If the cylinder retracts, then the load is on the piston side, which is a larger area than the shaft side and would produce lower PSI than if the load were on the shaft side. Lower PSI should mean less leakage than if the load were on the shaft side and appreciable leakage would be more apt to be through the spooling valve. Something like that. Confusing eh and probably means I'm about to learn something. A decent test although not the best is to disconnect the cylinder lines, which takes the valve out of the system.
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2003-11-20 69169
Of course any time you disconnect lines you run the chance of introducing air into the system, and since air is compressible it might skew your results, you wouldn't know if it was seepage or air compression allowing the motion.
Best of luck. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-11-21 69223
Missed that one. Yes, the quick disconnects wouldn't seal immediately which may put some air in the lines particularly if all the load wasn't off a cylinder. I imagine that most times any air would collect at a high spot in the lines and any compression would be immediate but it's one of those fine issues that I find interesting.
I think I got the other half of the idea Paul mentioned after posting yesterday. The way I'd say it is that movement of a piston displaces more oil from the piston side than from the shaft side. For a given movement of a piston a greater volume would have to leak passed the o-rings into the shaft side than into the piston side. Seems like that would tend to pressurize the shaft side and greatly slow any leak-down. Think I've got that right and it's my confusion precedes learning bit for the day. ....
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2003-11-21 69225
It normally is the valve that leaks as stated. The amounts of settling here doesn't seem to be out of line. I am amazed that Bradco is just moving away from leather seals at this time. I didn't know they were still using them. ....
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