JD790/419 Loader drifting down

[BGL990]

It's not necessarily an old wives tale. Depends on the design of the seals I think. Many seals have backup O-rings or actual springs coiled around the inside lip to help press them against the shaft. Many don't. Seals that don't may rely on fluid pressure behind them to force them against the shaft. If there is no pressure at all behind them, it is possible for them to seep a bit. I think it was somewhere here on TBN that I read about this happening with a forklift. Someone noticed a seepage in the lift cylinder of a forklift. Replacing the seals didn't help. The problem turned out to be that an employee was dropping the forks to the ground at night, relieving all hydraulic pressure in the cylinder and letting the seals seep. A rep. for the forklift company told them to keep it lifted up a couple inches when not in use and that solved the problem.

I have an old post pounder that blew a seal. The only replacement I could find came with an O-ring backup fitted in side it but that made it too stiff to insert into the cylinder cap. The company I bought the new seal from said to just remove the O-ring and it would still be OK because the hydraulic pressure would keep it tight when in use.

I think many quick connects use a similar mechanism - pressure behind the rubber seal in one connector forces it against the metal of the mating connector. The more pressure, the tighter the seal.

Edit: I added a crude drawing of what I'm talking about. If there is an O-ring or spring backup, it would be inside the seal lip where the arrow is pointing, but often fluid pressure and the rubber stiffness itself is all that presses the seal to the shaft.

 

[N9PDL]

I have posted about this very subject here before. My 790/419 loader leak down at an unacceptable rate. The dealer has replaced every hydraulic component under warranty (all cylinders and SCV valve) and it still leaks down very fast. When driving around with the loader on the front, I constantly have to "tweak" it up. With a load in the bucket, you can actually see it going down! JD's response is that this is normal. It is not normal to leak that fast and in fact it is a safety issue! My only thought is that the SCV was built with sloppy tolerances or something. The dealer doesn't know what else to do. I'm considering trying to get a new loader and/or tractor out of the deal.

 

[timb]

Can't say if the 790 should be that fast, but there are definitely better and worse quality components out there. If you look at just the simple chart posted earlier it's obvious that the more expensive models have tighter tolerances and/or more sophisticated designs. That trend continues upward in the Deere line - the 5000's have tighter tolerances yet (and lower 'acceptable' leak down rates).

Question - whether leaving a little pressure on a hydraulic component when parked is actually beneficial or not - is there any harm in doing so (other than the safety factor of a sudden drop?) I could park mine in the bay with the loader bucket a few inches off the ground with virtually zero risk. If it coudn't hurt, and *might* just help - then I may try to remember to park things that way.

 

[creeper]

I have read your earlier post, Im sorry to hear your goin thru all of that,let us know if your dealer does the right thing.Good Luck.

 

[JerryG]

The way seals are made they should be self sealing when the system is not pressurized. As the pressure is increased, sure the seal is made to increase pressure against the rod. If it didn't it wouldn't be able to handle the pressure.

 

[BGL990]

Agreed - seals *should* always be self sealing, there just seems to be some evidence that it isn't always the case, even with new seals. Whether it's microscopic scratches or roughness on the shaft, seals stiffening up in the cold, wearing the wrong color socks, or whatever, it seems that sometimes they seep a bit and a little pressure behind them might help. I don't mean that leaving an implement in the air is a cure for bad leaks. Obviously if it's anything more than a bit of sweating, there is a problem.

Personally I don't have any problems with leaving my loader or 3pt lifted a couple inches off the ground. I wouldn't leave them up high unattended, though.

 

[BGL990]

Sounds frustrating. I would concentrate my attention on the SCV, as it sounds like you are. If you think about it, aside from external fluid leaks, the SCV being sloppy is about the only thing that would let the loader drop all the way down. Even if the internal seals in a cylinders were totally gone, if the hoses to that cylinder are completely sealed off, the rod cannot move much. Extending or retracting the rod changes the total volume of oil in the cylinder and that oil has to go somewhere or come from somewhere. Even if you took the internal seals out of the cylinder and connected it's two ports together you won't be able to move the rod very much unless there is a bunch of air inside.

Some might cringe at my next suggestion, but I'd do it ... /forums/images/graemlins/tongue.gif

Have you tried lifting the loader a foot or two and unplugging the hoses? (Of course be careful, lower the loader onto blocks to relieve pressure while unplugging and then knock the blocks away. Use a jack to relieve pressure again when you re-connect). If your quick connects seal OK, the loader should only drop a bit due to whatever air might be present and from hose expansion, but it shouldn't continue to drop past that. If this is the case then it further points to the SCV.

ps. The loader on my 990 has also always leaked down, even when new. Just not as fast as yours. Maybe a foot or so overnight. I also have an old Ford 9N with homemade loader that will drop from full height to the ground in less than 10 minutes, so I know how annoying it is to have to keep bumping it up as you drive.

 

[glalonde]

What I do not understand is the internal differences between the loader hydraulics and the 3pth hydraulics. I can leave a 600 lbs ballast box on the 3pth off the gound for weeks, without it going down.

 

[Maine_Polack]

On the same rig you have, I had to have the SCV valve replaced under warranty.
Riding for 10 minutes the curl on the bucket would have to be lifted at least 3 - 4 time, to keep from dumping stuff out. Now I still have to do it usually once. Apparently this is in step with JD specs. What you are experiencing is certainly extreme. I would also like to know how it turns out. Too bad you have to fight so hard to just get what you paid for.

 

[Jim_Fisher]

N9PDL,

</font><font color="blue" class="small">( With a load in the bucket, you can actually see it going down! JD's response is that this is normal. )</font>

Did JD provide you with the allowable leakdown specs for the 419 loader?

Deere has a page on their site which lists the allowable leakdown rates for 410/420/430/440/460 loaders. Instructions on how to diagnose the source of the problem are included. The diagnostic instructions are quite generic and would probably work with most simple valve and cylinder applications.


Loader and backhoe boom/bucket lower slowly while parked

I had a similar problem develop on the curl circuit of my 430 loader when it was less than three years old. I traced it to an internal cylinder leak. I rebuilt the bucket cylinders and the problem went away. Shortly after, the boom cylinders started to do the same thing. Same problem cured by the same solution.