Cockshutt/Oliver 1655 Hydraulics- Flow But No Pressure

Hey Guys,

I have a Cockshutt 1655 with a brand new hydraulic pump. There is lots of flow out of the pump everywhere a line can be cracked to check, but absolutely no pressure. There's no pressure to steer, no pressure at the outlets. The tractor seems to have pressure for a couple of seconds at start up, but besides that NOTHING.

Hydraulic valves have been removed, cleaned, and rebuilt with new O-rings and new springs. New filters and breather installed when pump was installed. Any ideas what could be causing this? Is there some way that pressure can be turned up or adjusted on this pump? Hydraulic pump is internal so I'd like to figure this out before it has to be torn into again. Thanks for any help!
 
a pump with no pressure. If it seems to build and drop I'd say it's in the pump. I've used and retired several hydraulic
jacks, when they fail they do the same. I'd start at the coupler and work back, but it sounds like the pump to me unless
it's just not installed right and bleeding right back in the the case.
 
Initial thought is that flow and no pressure would mean that you have a relief valve set way too low or open all of the time. This would not
allow the system to build up working pressure. I don't have my I&T manual in front of me right now to see if they have a schematic but will
look tonight. Others may have more info before then, hopefully.
 
Relief valve was my initial thought but that doesn't appear to be the issue, I have fiddled with the valve block to no end, installed new springs, new o-rings, etc. and no results. Is there any way to set pressure on the pump? I don't recall adjusting anything on the pump when I installed it, and of course it is internal way down in the rear end so everything has to be taken apart to get at it. A pretty poor set up in my opinion.
 
If you have an I & T manual and could post a or send me a schematic that would be great, I have a technical service manual that the cover says for a 1655 but the schematics on the inside look like a different hydraulic system. Maybe 1650???
 
The I&T manual has only a schematic for a 1600, so it would be similar to what you already have for reference. Manual says that only difference between what they show for 1600 and later series is position of
oil filter in system. There is no adjustment shown for the pump, but there is another relief valve shown in the flow divider valve for the power steering system. Flow divider valve is on the left side of lift
housing for 1655. Have you checked to make sure that spring is OK? Have you put a gauge in the system to see if there is any pressure build up? Just wondering. Hope this helps.
 
I wonder if what causes the pump to operate is slipping. Here's a silly question and I only ask it because I have
equipment that it really matters, Do you put the right kind of fluid in?
 
I had a 2-70 do that a few years ago. Same thing as a 1655 The relief valve works on the principal of differential pressure. If the orfice in the plunger of the relief gets plugged with a spec of dirt, you only have about 150-250 psi of hydraulic pressure if my memory is correct. I got the hole cleaned out and life was good.
 
I have removed the hydraulic valves, cleaned them all out, replaced the springs and o-rings. Didn't seem to make any difference.
 
I'm sure you've checked this already, but if your pump is good, and your flow is good but you have no pressure, then your safety relief valve (p/n 107129AS) is probably broken off and laying in the bottom of your hydraulic housing. The pipe fitting elbows used to hold it on break, and/or get knocked off inadvertently when re-installing the hydraulic housing if you're not careful (I know, I've done it).
 
I uploaded a schematic and you can see the relief is before everything else directly after the hydraulic pump. There are 2 styles of relief valves. The earlier one was just a spring reacting on a poppet. The newer one is a spool that moves in a cartridge. Part #92 in the first picture is where I had my issue. If you remove the cartridge and spool together you can use shop air and the valve easily moved. However there is an orifice in that spool that allows a very small amount of oil to reach the other side. If that hole gets plugged like mine did, you only have as much hydraulic pressure as the spring can handle. Most likely less than 120 psi. If the hole is open and oil can reach the other side, it creates differential pressure to help hold the relief shut with little spring pressure needed. I think I had to disassemble the spool somehow to see the small hole that was plugged. I used a torch tip cleaner drill to get the orifice cleaned out. It had some metal in the orifice from the hydraulic pump that was starting to come apart with less than 250 hours of use. There was also a screen before that cartridge that would have prevented that issue but was damaged. Part #88. I'm not sure if this is your case or not, but I got lucky on this one. I would have installed a new pump and had no pressure. The lift cylinder safety valve should only cause 3 point issues.
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Thanks for the help guys. No luck yet. I was hoping to avoid taking the hydraulic housing off again but maybe I will have to go ahead and dig a little further in to it.
 
mkuhns any way you could email that picture directly to me so I can blow it up? Kind of hard to see on my laptop screen. Don't think I've seen that picture or schematic anywhere in my books.
 
First of all there were 2 different hydraulic system available> Does your tractor have a 3-point hitch. Remember pressure is called by restriction to flow.
 
You have to type in your email below your name before posting for me to send it to you directly. You can hit control + or control - at the same time to make the picture bigger or smaller on your screen.
 
Thanks again for the diagram, I got it blown up. I will get back at the tractor this weekend and it will help.

Yes the tractor has 3PTH.
 

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