John Deere 300C Backhoe Loader Hydraulic Pump Leak

MD500 · Jun 27, 2014

I have a 86 JD 310 Backhoe Loader and the hydraulic pump has a leak that no matter what I replace just keeps leaking oil. There is hex head I believe a pressure relief valve that screws into the front of the pump that has a O ring seal at its base and small shaft that has a O ring seal and a nylon bushing. I have replaced the outer o ring with every type of o ring and it just keep leaking. Everything works fine on the thing except for the puddles of fluid it leaves everywhere. I have taken the vale to several hydraulic shops and they have put numerous o rings on it but no seal. I have inspected the valve and the base of the pump and there are no pits or corrosion just flat surfaces. I am going to try to attach a pic of it and would appreciate any suggestions or comments !!!!!!

Tx Jim · Jun 28, 2014

Have you checked for a crack in the valve housing?

J_J · Jun 28, 2014

You can replace all the seals you want, but if the pump shaft has a groove worn in it , it will leak.

How can a hyd shop give you back a pump that leaks if you ask them to fix it.

Do they not test anything they fix?

MD500 · Jun 29, 2014

Tx Jim said:
Have you checked for a crack in the valve housing?

I should have caught this but it is so small it took a magnifying glass and the relief valve had to be tightened before you could see it. Where the relief valve screws into the housing there is small micro crack in the housing that is allowing the fluid to seep out. When the relief valve is not tightened up the crack is not noticeable.

Anybody know where you can get a valve body without spending a grand for new pump ???

Gale Hawkins · Jun 29, 2014

I would check with a good welder and not over tighten the valve but not sure if that would be a solution but would give it a try on our 1983 310B. It came with a light green pump so I expect years ago it was replaced.