Go BottomHydraulics question
 | Bryan Hockensmith
Join Date: Posts: 1 
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2000-11-11 21394
What is the proper procedure for adding a new hydraulic cylinder to a system? I've got an '87 JD 650 and I'm adding a hydraulic toplink to the 3-point hitch. The hydraulic toplink is a new cylinder and hoses, so it occured to me if I just connect the hoses and use it, it will introduce alot of air into the hydraulic system. Is this a bad thing? I would assume the hydraulic system is just like a brake system...air in the system needs to be bled out. How do you do this with the hydraulic system on a tractor?Thanks,Bryan
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| Roger L.
Join Date: Jun 1999 Posts: 0
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2000-11-11 21395
Howdy Bryan. Those hydraulic toplinks are really nifty devices. It surprises me that all tractors don't come with them. We will need a bit more information to hook it up properly.
Does the hydraulic top link have its own actuating valve? If not, how is it controlled?
Do you have a loader or any other type of hydraulically operated implement on the tractor other than the 3pt itself?
How about the remote power steering that JD offers for the 650? Does it have that? If so, does the PS get its fluid from an add-on hydraulic diverter box about 1x4x5 inches mounted down by your feet?
What does the hydraulic top link kit have to say in the directions? Anything special required?
Roger L.
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York 
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2000-11-11 21397
I trust you have the valve to work from. The air will bleed out into the tractor with out any trouble. By the time you cycle the cylinder a few times the air will be gone. ....
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2000-11-11 21401
Bryan, don't forget to 'top up' the hydraulic system on your tractor. When you add any new hydraulic 'parts' to a system for the first time you will (as you already know) purge the air out of the new parts of the system, the oil level in the entire system will then be lower by the same volume as the air you replaced with hydraulic fluid. Likewise, be sure to always detach your hydraulic implements (especially your loader, if your tractor is so equipped) with all cylinders in the same position (preferably with all of them as 'closed' as possible) so that the transmission & hydraulic sytem (and normally brakes) are operating in, and with, the proper amount of fluid. Best of luck. ....
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| MikeC
Join Date: Posts: 1
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2000-11-11 21411
Speaking of the "proper amount of hydraulic fuild", how important is that on a hydro drive tractor? My JD855 is a bit over-filled at the moment. Will that cause problems or reduce performance? Thanks. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2000-11-12 21419
Filling to correct levels is a good idea. However, there probably is a margin for error with overfilling. Maybe somebody who knows your particular tractor will respond.
I'm commenting, because I'm not sure you got a direct answer to your question about brakes and tractor hydraulic systems. No. They are not the same. Vehicle hydraulic brakes are closed systems, while tractor hydraulics are open systems. In properly working tractor systems, any air present tends to be expelled into the return line and bubbles out of the oil in the reservoir before returning to the pump. Abnormal conditions like a cracked or blocked suction line (from the reservoir to filter and pump) can put more air into the oil than bubbles out. However, in such cases, the hydraulics operate poorly and froth can be seen on the dip stick. Prolonged operation can damage the pump.
One thing to get used with tractor hydraulics is that (with open centred systems) oil is pumped continuously through the system. When a hydraulic device is operated, the 'open centre' is closed, which diverts oil to a particular cylinder. Oil is pumped into the cylinder until the centre is re-opened, or until the system pressure is exceeded. System pressure is exceeded when the cylinder reaches the limit of its travel, or when attempting to lift a weight beyond the cylinder's capacity. A pressure relief valve opens when system pressure is exceeded, which diverts oil back to the reservoir through the relief valve. You will hear a howl or whine when the relief valve opens. A tractor shouldn't be operated for long periods with the relief valve open. The valve is smaller in diameter than the regular lines, and the oil can over-heat. Another whine you'll hear is the power steering. The power steering sound is normal, but the relief valve sound (for longer than a few seconds) isn't. It's good to know the difference between the two sounds.
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| Roger L.
Join Date: Jun 1999 Posts: 0
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2000-11-12 21422
OOPS! Bryan, I mistakenly thought that you were looking for info on how to hook up the hydraulic third point....I got it confused with another conversation. Glad its not the case, because your question on the air is easier! Exactly as Tom says: In an open system the bubbles just rise to the surface of the reservoir and are vented out. You don't have to bleed anything; the hydraulic system purges itself. The only exception to this is when you have entrained bubbles within the oil itself - think of it as frothing. You will get this with some systems and some oils. But you can't do a thing about the entrained air other than to use a combination transmission/hydraulic fluid which resists frothing in your tractor. One of JD's combo trans/hydraulic fluids is called JD303. I believe that it is what is recommended for your tractor, but you might want to check it out. On a general note, if your system seems to be real sluggish in cool weather and prone to frothing, remember that JD303 is more expensive than regular lubricating oil (which does work) and it is not unknown for used tractors to have regular oil rather than trans/hydraulic in them. ....
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| Bryan Hockensmith
Join Date: Posts: 1
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2000-11-12 21444
All,
Thanks so much for the quick education on tractor hydraulics. I finished welding the hydraulic toplink and installed it today. It works like a charm. I topped off my fluid levels after extending the cylinder all the way and everything looks good. Amazing how much easier the hydraulic toplink makes switching implements.
You guys were much more help than my dealer (considering he closed at 12:00 on Saturday!).
Thanks again, happy tractoring.
-Bryan ....
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