Hey ya'll first post here:
I'm fixing a JD 4100 compact tractor for a friend that has a 410 loader. The loader was not lifting properly so I did the obvious and cleaned the suction screen, changed the filter and put new JD hydraulic oil in it. It seemed to work great...for a minute. Even before then I did the test where I switched D&C to A&B to see if it worked and it sort of did work better. Then I put it all back and disconnected D and it would go up and down. I disconnected D and connected C and it went up and down. It seems to work like this but it does not have much power.
Based on my research there are two possibilities: 1. one or both of the End Lift cylinders have an internal bypass which would suck. OR, there is a clogged relief valve in the control unit or busted o-ring causing pressure to bypass so the thing won't lift cause it has pressure on both sides of piston.
How the heck to I figure out if it is one or the other? My first idea was the remove C and then take the quick connect off so it was open. Then I started the tractor and tried to lift and fluid came out. So that makes me think it's bypassing. Or it could have just been, you know, emptying that side of the cylinder and displacing fluid but I don't think so.
I'm trying to be methodical about this but for real the JD parts site isn't working so I can't examine what the inside of the control valve looks like so I wouldn't know what or where the relief valve is or how to test it. Maybe I need the technical manual or just a good common sense injection.
(the bucket seems to dump and come back just fine.)