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John Deere Tractors Discussion Forum
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John Deere 300 Industrial hydraulic problems

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Richard Harrison

07-10-2008 07:59:46

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I have a 70's John Deere 300 Industrial tractor/loader (similar to a 1020) with a JD9250 backhoe attachment which has served me well for 15 years of occasional use. Recently, it has developed a hydraulic problem. First, after using it for hours, suddenly the loader and backhoe would not operate at all. Engine runs fine, transmission fine, tractor moves fine. No funny noises, just no movement on the loader or backhoe. After about 10 minutes, hydraulic function came back, then came and went intermittently.

The next day, tractor ran fine for about 30 minutes, then the same intermittent loss of hydraulics. Next day, same thing. Oil level is fine.

I thought it might be clogged filters, so I changed both hydraulic filters (the transmission one and the loader return one. I also changed the hyd. fluid. The oil fluid and filters were clean as new. So I started it up, let it idle to self-purge for about 20 minutes, and it operated fine for about 5 minutes then, intermittently began to lose hydraulics, with occasional shuddering and air banging around in the lines. No amount to extending/retracting of the cylinders would clear them out. I have changed fluids on this tractor before and never had this problem. It feels like air is being sucked into the lines somewhere, but hoses and lines look tight.

Sometimes the machine runs normally. It has plenty of hydraulic power, plenty of bucket lift. It can easily lift the tractor with down pressure with either the front loader or backhoe. It can run this way for minutes. When it is running normally, it sounds normal. This makes me think the pump is okay.

Then, suddenly, no pressure. If a bucket happens to be up, it stays up until you put it down. Then nothing. At this point, it still sounds normal, no click-click-click like it is out of oil. If you hold a valve open, no pressure, no funny noises. It can be like this for minutes at a time. RPM doesn't help. Then, sometimes, the cylinder will start to move, slowly as it builds up pressure. Sometimes the whole tractor will shutter loudly as the cylinder ratchets up. You can hear air pinging around in the lines. Sometimes, after shuddering for a few seconds, the pump will "catch" and pressure and operation will be normal for a minute, or so. Then, it goes off-line again.

The problem seems to more related to the loader than the backhoe. In fact, when the loader cylinders are "dead", if you open the backhoe valves and move the backhoe pistons a bit, you can restore pressure to the loader for a while. The tractor itself always has moved forward and back on its own.

It does seem like an air suction problem, but I am not sure. I am not very familiar with hydraulics and would be grateful for a point in the right direction to troubleshoot this problem.

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Mike Gray

09-23-2008 17:42:09

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 Re: John Deere 300 Industrial hydraulic problems in reply to Richard Harrison, 07-10-2008 07:59:46  
You can't just leave us hanging! What was the outcome of the hydraulic problem? Please get back here and post the end of the story.

A Fellow JD 301 guy with the backhoe

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Richard Harrison

09-26-2008 08:18:44

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 Re: John Deere 300 Industrial hydraulic problems in reply to Mike Gray, 09-23-2008 17:42:09  
Thanks for your interest. I have only had a couple of hours to spend on the machine, but in addition to the symptoms described above, I ran the pressure test of the oil going to the front hyd pump--at the oil cooler to resovoir hose. With the machine cold, I could get only a few PSI, which went away as the oil heated up. But i started the engine briefly with the transmission filter off and oil squirted out strongly. So, I think the transmission oil pump is ok.
Basically, it seems that the oil is not getting to the front main pump, especially when warm. I suspect (and hope) something in the reverser is bad.
If you have any suggestions, let me know. Otherwise, I will post the results if I ever figure it out.
Thank you,

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Mike M

07-10-2008 12:38:37

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 Re: John Deere 300 Industrial hydraulic problems in reply to Richard Harrison, 07-10-2008 07:59:46  
Did you also clean the suction screen in the bottom of the tranny ?

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Richard Harrison

08-17-2008 06:37:18

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 Re: John Deere 300 Industrial hydraulic problems in reply to Mike M, 07-10-2008 12:38:37  
I am now just getting back to this tractor problem. 1. I cleaned the suction screen, which was about 20% clogged with black rubbery stuff. Hyd. oil was clean, no water or silver color. Did not fix problem.

2. I checked the transmission bypass valve- was clean

3. I installed pressure gauges on the main pump (which is a serial # tagged 2.4 inch pump)--I believe the right side top port is pump output and the lower port is feed pressure from the transmission. The output pressure immediately jumps up to 2200 psi,even at idle rpm, that's good, but the charge pressure was maybe 5 psi, or less. At high rpm, the output would stay nicely at 2200 psi, and the charge pressure would slowly creep up to 20 psi. When a cylinder was activated, the charge pressure drops to 0. After the cylinder action is stopped, the charge pressure will creep up to 1-5 psi. After about 10 minutes of running, the charge pressure drops to zero and the output pressure becomes erratic, ranging from 2200 to 0.

Before heating up, the machine has plenty of power for digging or loader lifting. After warm-up, it becomes slow, weak and erratic. I noticed the Hydraulic oil reservoir tank is empty after running, and had a slight suction when I opened it (tractor off). No sign of hose kinks or dents anywhere.

4. I felt all the backhoe and loader valves for temperature; all stay cool except the steering column, which gets noticeably hot within a minute or two of running. For years, the steering has always been a little quirky--occasional interactions between loader operation and steering, occasional no power steering with a heavy loader load.

1. How does the pressure control (priority) valve work? Does it shunt transmission charge pump pressure to the steering gear, or does it send main pump pressure preferentially to the steering?

Would a bad pressure control valve cause the main pump charge pressure to be so low?

2. What about the heating of the steering column? Would internal leakage cause the low charge pressure? Does the steering work on transmission pump pressure or main 2200 psi pressure?

3. Is there a way to test the transmission oil pump independent of the steering, or to plug off the steering for testing?

I got a new stroke control valve and plan to change it, but that does not seem like it will cure the problem. Any other suggestions/

Many thanks, Richard

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Richard Harrison

07-10-2008 16:49:17

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 Re: John Deere 300 Industrial hydraulic problems in reply to Mike M, 07-10-2008 12:38:37  

Good question! The symptoms sound like a plugged intake.

I looked for the suction screen to clean it and could not find it. My manual shows it as a square-headed finger screen on the right side of the tractor next to the upright transmission-hydraulic system oil filter housing. But there are 3 or 4 large hydraulic hoses connected to a casting in this area. I think these are associated with the backhoe. Is the suction screen located under the small casting that these hoses connect to or somewhere else?<

p>By the way, my machine is a diesel with a reverser and hi/lo.

Many thanks for your help!

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Mike M

07-11-2008 04:59:53

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 Re: John Deere 300 Industrial hydraulic problems in reply to Richard Harrison, 07-10-2008 16:49:17  
For sure clean that suction screen ! You will also have to redrain your oil. Get some clean buckets and save it. Do you have a large plug appox. 2" OD ? on the Left hand side ? sometimes these have a sq. 1/2" drive built in the end others have the sq. sticking out ? Even if your old oil looked clean you could have brake facings or just jelled oil that looks like vaseline on the screen.

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07-11-2008 04:17:24

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 Re: John Deere 300 Industrial hydraulic problems in reply to Richard Harrison, 07-10-2008 16:49:17  
should be a short hose between filters and tractor, the screen is behind that hose.. has hex hose fitting..


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Richard Harrison

07-13-2008 05:50:28

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 Re: John Deere 300 Industrial hydraulic problems in reply to cannonball, 07-11-2008 04:17:24  
Many thanks for your reply. When you say the suction screen is "behind" the hose fitting, do you mean it inside the hose fitting--you have to remove the hose and the hex hose fitting from the transmission housing and the intake screen is inside where the fitting came out of?

Sorry to ask such a dumb question!

My tractor (JD300 loader/backhoe w/reverser, hi/lo diesel) has a loader return filter (the horizontal one) on the right side of the tractor with a short 3 or 4 inch hose (probably 3/4") from the filter housing back to a hex-headed hose nipple on the transmission case. My manual does not show this hose, only a square-headed intake screen cover plug in this area. I pretty much looked everywhere else for the intake suction screen.

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Richard Harrison

07-11-2008 05:34:47

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 Re: John Deere 300 Industrial hydraulic problems in reply to cannonball, 07-11-2008 04:17:24  
Many thanks, will check it out tomorrow!


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