68 JD 400 hydraulics acting up.HELP!

Oldchevyguy · Nov 30, 2025

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 · Nov 30, 2025

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

oldnslo · Nov 30, 2025

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 · Nov 30, 2025

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 · Nov 30, 2025

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.

Tx Jim · Dec 1, 2025

Before even considering replacing any hyd pump one should perform the easiest tasks first. It doesn't get much easier than changing the hyd filters & checking cleaning the hyd oil suction screen.

Next I suggest to perform good hyd diagnostic procedures before entertaining the thought of replacing any hyd pump!!!

Photo below is for an ag not ind tractor but round cannister holds 1 hyd filter & 2nd hyd filter is located near by.

JD 400 ind tractor has closed center 8 piston hyd pump in front of radiator with an internal stroke control valve that controls hyd pressure. If stroke control valve gets some foreign material in stroke control valve seating area it will affect system hyd pressure.

furnone · Dec 1, 2025

Oldchevyguy said:
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.

I had a 1970 JD 400 that had issues with the loader, it would work fairly well, although a little slow, until the oil heated up, then it would hardly lift at all. The backhoe and stabilizers worked like a champ. I tried everything I could think of, re manufactured hydraulic pump, rebuilt the diverter valve etc. I had the JD mechanic out to go over it and he was stumped.

About 2 weeks before I sold it, I read something about the steering valve having priority, taking pressure away from the loader. I removed the steering column and had a guy that worked at JD rebuild it as a side job. After I reinstalled the steering column, the loader worked like new.

This may be your answer too.

Tx Jim · Dec 2, 2025

As you determined replacing hyd components more especially frt hyd pump without performing good hyd diagnostic procedures isn't as good idea.

Several JD utility tractor steering valves have been known to have failed o-rings causing hyd problems. Simple hyd test is disconnect power steering supply line & cap pressure line orifice then check operation of hyd system.

Any large internal hyd leak can cause closed center hyd to not operate correctly.

true temper · Dec 5, 2025

The common problem is charge pressure. You need charge pressure for the transmission and hydraulics to work properly.
You can check the charge pressure on the main hydraulic pump.

Oldchevyguy · Dec 5, 2025

So I finally found time to change the filters and clean the sump screen tonight. I got the backhoe filter and housing off and unscrewed the hose connector so I could access the screen. Had a tough time getting it out had to keep working it back and forth and finally got it far enough out to grab it with some pliers and was able to work it out the rest of the way. It was definitely blocked up with sludge and it was collapsed. Should I be looking for a replacement or just clean it out and push it back into shape with a dowel or something? Does anyone know how available this part is? I have a parts list and will try and look it up tomorrow.

Barry 1 · Dec 6, 2025

My 400 uses a AR26375 and there are plenty available on Ebay and amazon etc, Mine was crushed and needed replaced. I see one on amazon for $24, most are around $32

Tx Jim · Dec 6, 2025

R53169 is a nylon instead of steel version of that AR26375 suction screen but it appears to cost about the same amount as the metal screen.

Oldchevyguy · Dec 6, 2025

Ordered one from EBay today. I’ll update when it gets back together and if it fixes the problem.

Leejohn · Dec 6, 2025

See you found it. I'm sure that well fix your problem, If not it well sure help.

GrandpaSmurf825 · Dec 6, 2025

Is it in good enough shape to put back in? If it's not badly damaged (no holes or crushed) clean it thoroughly and put it back in. The bigger question is what does the sump look like? If it's got a lot of crud in it then it really needs a good cleaning. From my research that has a piston pump. Hopefully it's not trashed it from starving for oil. If it cavitates you can hear it clearly believe me. What does the fluid look like? After the fact and no ever does anything with the fluid until they start having issues and then it may be to late. If it's dark that isn't a good thing. It should be pretty clear and light yellow.

Oldchevyguy · Dec 9, 2025

The filter was all collapsed, new one is due tomorrow. The fluid wasn’t dark or burnt but it wasn’t clear. It looks a little cloudy and kind of green- gray. I’m sure there is a little water in there somewhere. I tried to rake out the bottom of the sump as best as possible but it seems like most of the junk was sucked up to the screen . I bought the machine about 3 years ago and the previous owner said that he had it for about 20 years. Not sure if that screen was even cleaned before.

Oldchevyguy · Dec 11, 2025

So I got the new screen yesterday and installed it and put the filter housing back on to the fitting where the screen came out. Then I changed the transmission filter under the machine and put the filter and the housing back on the filter that goes to the back hoe. There is a rubber o ring that goes around the top of the filter housing on both filters and it seemed like a sloppy fit. In my mind I would have expected to have to stretch it a little bit to get it on. I checked the old ones and they were the same sloppy fit. I put it all back together but didn’t add any fluid until this afternoon and when I started it up it was leaking around both filter housings. I tried to tighten them up but no good. I took the transmission one back off and can see that the ring didn’t seat properly so now I’m at a loss. It’s not rocket science but I don’t see how it’s going to work better if I put it back and the ring is that loose. Has anyone had issues like this before? I changed one of these before and there was no issues not sure what I’m doing wrong.

Tx Jim · Dec 12, 2025

Are you installing quad ring in filter housing then installing filter & cap?

Oldchevyguy · Dec 12, 2025

Well, on the transmission filter I had the gasket on the cap because it was going straight up vertically and it seemed like the the thing to do because it didn’t want to stay up in thereby itself while you fight the spring in the cap to get the bolt started. The whole thing is awkward because the cap is heavy and your laying on your back. On the Backhoe filter I was able to get the ring to stay in the hole because it is in a semi horizontal position and it would not stay in place on the cap which on that one is even heavier and goes in on an angle while working it in around the hydraulic hoses. Both leaked. My inclination was to put them in the opening and stick them with some grease but I was afraid that the grease would affect the hydraulic system. Years ago I worked in a transmission shop and the builder used white lard to stick stuff like that together. Perhaps I could try some of that? How do you assemble it? I’m totally open to suggestions.

Tx Jim · Dec 12, 2025

As you previously mentioned try applying a slight film of grease to quad-ring to help hold quad-ring in housing groove. Many people have used grease to accomplish that same task in the past.