Some Hydraulics Help Please:

[ACKBill]

This one's for all of you guys that are comfortable working on the hydraulic system of your machines. I have a 3520 with a 300cx loader that I have had for about a month now and I have a problem with the hydraulics for the bucket. I believe that I have air trapped in the bucket cylinders because there's an awful lot of "play" in the bucket. I can rock the bucket at least 3"-4" and its not a result of any mechanical play in the pivots etc, you can see the rods moving in and out of the cylinders. I had hoped that the air would find its way out as I used the loader but with 15 hours on it in the last couple weeks (digging, grading and snow removal), there's been no improvement. So, my question is this... Is there a way to bleed the air out of the cylinders? I had thought about just loosening the hose fittings a little, one at a time and then applying pressure either by rocking the bucket by hand or by cycling the bucket control but I really didn't want to wear a couple of quarts of hydraulic oil or damage any of the o-rings or seals. Someone out there must have had to deal with this before like when changing hoses, any suggestions?

Thanks!
BILL

 

[gator]

Cycle you bucket full curl, full dump a few times, if its air, it will clear.

 

[ACKBill]

Wally:

That was what I tried first, and still no joy. I just don't understand why I can't clear the air unless I'm sucking it in somehow but I'd think that I'd see a leak somewhere if things were loose enough for that to happen,

BILL

 

[MadReferee]

What makes you think you have air in the cylinders? Moving the bucket from full curl to full dump a few times will purge any air. I doubt you are sucking air because if you had a loose fitting then it would be leaking when the cylinder moved in the opposite direction. You may have other internal issues with the cylinders.

 

[ACKBill]

I believe that it's air because it "feels like" air. In other words it's bouncy for lack of a better way to describe it. There's no harsh or hard feeling to it like there might be if it was mechanical. I've gone over all the mechanical connections that I could find and they are all tight and don't have any slop in them. I agree with you, if the fittings were loose enough to draw air through them, then the should be leeaking really badly. I am better than average with a wrench but I don't have a whole lot of experience with hydraulics so I'm hoping that someone here can give me a lead to follow. What kind of internal problems could the cylinders have that might produce this kind of springiness?

Thanks,
BILL

 

[gator]

I think what Mad is talking about is fluid bypass internal in the cylinder.
A few questions:
Has it always been springy?
Does your bucket slowly (or fast) dump itself with a load?
To check for internal cylinder leak, with weight in the bucket, set it to slight dump, disconnect your curl/dump lines quick disconnects on your selective control valve. If your bucket dumps, its internal cylinder leakage, if not it may be control valve leakage. Reconnect the lines and try this again, it it leaks down than it may be your SCV spools leaking internally.

 

[kwyatt]

I have a 3320 with the 300CX on it and to be truthfull I have not had it that long or tried to move my bucket by hand. I am offshore now but when I get back home I will try mine. Only real internal cyl problem that can develop is bypass around the outside of the piston or if the piston head is bolted to the rod bypass from the high pressure side to the low pressure side. You can see that with a pressure gauge but you would have to add them in the system. If it is bad enough you will get leak down under load and the bucket will try to dump itself over time. Another way to locade bypass is to extend or retrack the cyl all the way, open the the line on the return side and see if you get any fluid flow. Problem is you will need to bleed the system but that shouldn't be that hard. As Wally said if you have trapped air cycling the bucket should send it back to the tank. In general air in a system will cause jerkyness and noise during operation

 

[ACKBill]

Wally:

In answer to your questions:
Yes, it's always been springy. Like most I thought that it was air and would work it's way out with use.
Bucket rolls and curls at about equal speeds (fairly quickly) loaded or empty and I haven't noticed any sagging in the bucket when it sits ( I had the forks on today with the snowplow from my P/U on them and it didn't sag at all while sitting.

I'll try the test you gave me tomorrow and see if I get any sagging (leak-down).

Thanks for your suggestions and help.
BILL

 

[ACKBill]

Kwyatt:

That's about what I was thinking as far as cylinder problems go. Realistically speaking, they aren't all that complicated, there's only a limited number of things that can go wrong with them. Anyway, I'll let you guys know the results of the tests that Wally gave me.

Thanks again for your help.
BILL

 

[ACKBill]

Wally:

I tried your test this evening. I cycled the bucket from lock to lock 12 times (trying to cover all the bases) and then I undid the QC's like you described. When I went to reconnect them I had to release the pressure in order to get them to latch and I got a small bubble of air out of them. Not a lot but I wouldn't have expected to get any at all so I re-connected everything, cycled the loader a couple more times and the checked for "bounce". It was way less! Tomorrow I'll do it all again and hopefully that will take care of it. /forums/images/graemlins/grin.gif It's cool that all the members here are so knowledgable and willing to share that experience with the other members.

Thanks to you guys for sending me in the right direction.

Bill