Oliver 77 hydraulics at my wits end

popcornob

New User
Good day.

I had posted a couple months back. Centerplate helped me out quite a bit heres a quick synopsis: replaced centerplate valve seat for poppit and had a new poppit machined for me. Put it all together and started getting 400 psi which was way better than 100psi.

I put a tee in the main bucket lift line and ran it to an on dash psi gauge so I could troubleshoot. When I raise the bucket and top out the tams it will go to 400 and start settling backwards toward 300. There are no fittings leaking that I can see.

One night without me pulling the lever I had it running and it slowly climbed to 850psi then some fittings were leaking so I shut it off and tightened the fittings but haven't got it past 400 psi since.

This tells me the pump is making enough pressure and the poppit atleast seats sometimes. I just wanna give up at this point, any help would be great, thanks.
 
I'm not familiar with 77s but any hydraulic system will only develop enough pressure to overcome the load. Does the pressure increase when the cylinders hit the end of the stroke and it goes on relief? Could be the pump or a worn valve leaking internally.
 
I'm not familiar with this one either. So some general and common things though. Is this a loader with single or double acting lift cylinders? Trip bucket or hydraulic bucket? If it is double acting with a hydraulic bucket you can swap the lift and bucket hoses on the valve to see if the problem moves with the hoses. Or try unhooking the lift hose from the valve body and install the gauge in place of the hose (removing the cylinders from operation), dead heading that circuit and see what you have for pressure when you operate the control valve. That will eliminate the cylinder packings which could be leaking by. If you still have low pressure the problem is either in the control valve or pump. The main relief valve in the control valve could be bad.
 
I've owned several of those,but like everybody else who's replied,I never worked on one. Best bet for an answer would be to repost on the Oliver Forum. Sounds to me like a lot of wear in the pump or a bad relief valve,but I can't tell you how to diagnose it.
 
The loader is entirely double acting. The relief valve is the poppit and seat i replaced. The pump wasnt to warn, the word i heard on that is as long as its not worn in enough to cut you, I am no expert so THIS could still be the case-- problem is I have ripped it all out of there so many times I dont wanna do it again just to see what I have seen already.

I attached a picture that explains the basics of this system.

Also I had the gauge dead headed on the port and got similar readings as I do with the T and the gauge cluster mounted one. I just dead head it to the top of the rams stroke to see pressure.
mvphoto45428.jpg

[/img]
 
Double acting cylinders,at this point I'd be looking at those. Have you tried plugging a gauge in to a remote and seeing what kind of pressure you have there?

The Du-Al loader on my 1600 had a leak inside a cylinder and would barely lift,sometimes not at all and that one had a cylinder blown on the inside. Somebody on the Oliver forum was at wits end with the same problem and that one turned out to be in internal problem with a cylinder too. They wouldn't leak down because there was no place for the oil to go once it had bypassed the leaking internal seal. The pressure just equalized so they stayed right where they were. On those Oliver systems,that oil won't re enter the system from the top end of the cylinder until you move a lever with the engine running to open the valve and let it pass.
 
The reason for installing a gauge as a dead head (connection to the cylinders are removed and the gauge blocks that port off completely, oil only goes as far as the gauge) is that when the cylinder deadheads at one end or the other; an internal leak in a double acting cylinder can go by the cylinder piston packing and exit the other side of the cylinder, which is open to return to the reservoir. If you had it completely deadheaded (cylinders disconnected from the valve) and still had low pressure, I would believe it is either a relief valve or pump problem. Is the power on the bucket better than the lift? Checking pressure at a remote as rrlund suggested only takes a few minutes and is a good check.

Any appreciable wear in the pump gears and plates can let oil escape and lower pressure the pump can build and maintain.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top