Go BottomBleed power steering
 | Reg
Join Date: Jul 2003 Posts: 3 CT. 
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2002-05-13 38573
Hi all, Could use some help.Just replaced the hydraulic pump on my tractor. It's a stacked pump, one side for tractor hydraulics and the other for power steering. The hydraulics work fine but the power steering is very hard and jerky. Could this be caused by air and should I bleed the power steering system.If so how should I go about it. Thanks in advance. Reg Lamson
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2002-05-14 38579
I'm guessing that what is called a stacked pump is what I'd call a pump and priority valve. The valve and pump are separate components, and the original valve probably was installed on the new pump.
For the most part, PS systems like remote hydraulics are self-purging and don't require bleeding. Air in the system is pushed through to the sump where it bubbles out of the oil. Rarely cycling is used to thoroughly purge air from a cylinder. Cycling is simply moving a cylinder to its limit of travel and holding for a few seconds. The PS also could be cycled. However, I'm not sure from the description if the wheels will turn all the way to their locks. I'm also not sure from the description if turning the wheels produces the sort of squeal many PS systems make in operation and whether the engine load can be heard to change.
If there's no sound or change in engine load, I’d guess that the priority valve is obstructed. Probably something entered the valve during pump installation. Priority valves have spring-loaded plungers that meter flow to the PS. Oil flow to the PS line goes through a small orifice in the centre of the plunger and could be easily plugged. A stuck plunger or broken spring could produce similar results.
A repair manual should give disassembly/inspection procedures for the valve. The only procedures in my manual are to clean and lubricate parts, check the cylinder for scoring and the plunger oriface for obstruction. The procedures are easy to do but probably shouldn't be attempted without a manual and exploded parts diagram. A broken pressure relief valve in the steering sector could produce similar problems, but I'd look at the priority valve first because that was the site of the original work to replace the pump.
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| Reg
Join Date: Jul 2003 Posts: 3 CT.
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2002-05-14 38583
Tom
Thanks for the info. This pump however, is actually two seperate pumps stacked togeather and driven by the same shaft.The power steering has it's own reservoir.
You do have me thinking now though.The only reason I changed the pump was because a leaking seal between the two pumps allowed fluid from the power steering circuit to cross over into the tractor hydraulic side.And guess what? When the reservoir got low the power steering reacted just like it does now. I'm going to check that line from reservoir to pump, maybe I kinked it. thanks again, Reg.
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-05-15 38625
I understand the pump configuration now. Well, the post gave me an excuse to dig out my repair and parts manuals, so it got me to thinking as well. Good results all around. Hope you find the problem. ....
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