68 JD 400 hydraulics acting up.HELP!

[Oldchevyguy]

I have a 1968 JD400 backhoe and it’s been a great machine. Recently I was noticing a slight delay in engagement letting the clutch out before it got rolling and every now and then the loader would act a little jerky. It has a few minor leaks so I figured it was probably just a little low on fluid. Last weekend I started it up and it didn’t want to drive at all. I checked the fluid and it was on the add mark. I dumped some in and it was still a little low so I put in more and it was up to the mark. Now it wanted to move but was still a little sluggish on the take off. I shut it off and when I came back about an hour later it seemed normal. I chalked it up to need air to work out or something. Yesterday I drove it to my brothers house about a mile away all told and on the way the power steering didn’t work. Then after I got there it started working and but the loader was not working right, going slow and didn’t want to pick up. At one point that got better but then the backhoe inplaments started acting up and didn’t want to work but then the backhoe loader was good and the machine wanted to move forward and backwards. Now I’m really scratching my head. Today the drive engage was super slow and the loader and the power steering were taking turns throwing fits. I’m at a loss. Has anyone had this experience? I’m wondering if it could be the filter? I don’t get why it is playing musical chairs with the different functions. If nothing works I would believe a plugged up filter or a bad pump but you would expect it to be all or nothing not taking turns between the different functions.

 

[Leejohn]

Try a new filter also clean the sump screen if it has one.

 

[oldnslo]

I believe that model loader backhoe had the variable volume piston pump with load sense or pilot control. It could be that the pilot control is randomly getting a pressure signal or some crud is stuck in it.

Do you have equipment to take any pressure readings for diagnostic purposes?

 

[Oldchevyguy]

I do not . I have a lot of friends who are diesel mechanics and regular mechanics and I know a transmission guy, so it’s possible that I could get my hands on something. Where and how would I connect a gauge to get a pressure reading? Where would the pilot control be? Does that seem more likely than clogged filters or sump screen?

 

[Oldchevyguy]

A quick search on the internet and AI says that is not the type of pump that machine has. It does show replacement pumps and they are not described as variable volume. I have a parts machine with a new pump if the pump was the issue. When the implements are working there is no lack of power. They just take turns not working.