JD 4300 Hydraulic Problem

reasley · Sep 27, 2008

Good evening, I have a JD 4300 that has a hydraulic problem. I used the tractor all day today to shred and, late this afternoon, the steering started getting "tight," and the bucket wouldn't go up after going down. I was about 400 yards from my shop so I drove it there and parked it for a while. When I came back to start looking at it, I noticed hydraulic fluid leaking apparently behind the hydraulic pump. There were several hose clamps that connect the suction lines to the pump, so I tightened each of these (they all benefitted from tightening them), but the leak is still there.

Here's how the tractor's hydraulics are functioning:

1) low engine speed = no power steering, no bucket lift or curl
2) high engine speed = good power steering, slow bucket lift and curl, but unable to pick up much weight.

Right before I stopped for the evening, I looked at the hydraulic section of the factory workshop manual but haven't studied it closely yet.

Apparently the pump is a tandem pump, with the front pressure for the power steering and HST and the back pressure for everything else.

I have some ideas about what is wrong, but I don't want those to influence any on-line diagnoses from others. One thing that I will add is that I am guessing that my use of the extra SCV ports on the factory SCV to install two connections for my post driver at the rear (or log splitter, etc.) may be related. I am thinking that I may have hit the actuating lever for these extra SCV posts and they got locked in one direction for at least a period of time under load and I didn't realize it because of the intensity of the work and the noise. Note that this is merely a guess and is not based on finding the lever locked in one direction or the other.

Any help would be appreciated!

Richard Easley
Waco, Texas

kennyd · Sep 27, 2008

Sorry to hear of your troubles Richard

Just to clarify one thing...

Apparently the pump is a tandem pump, with the front pressure for the power steering and HST and the back pressure for everything else.

There are two pumps, one for just the steering, and the other is just for implements (3PH, FEL Rear Remotes ect.) The pump for the hydrostatic transmission is driven directly from the crankshaft at the rear of the engine.

If I had to guess (which I do since I can't be there) I would bet that a return line is leaking somewhere causing air in the system. Possibly a line got snagged while you where out shredding. I think if one of the levers was left ON you would have noticed the sound of the system in relief.

reasley · Sep 27, 2008

Good afternoon, Kenny --

Thanks so much for the response!

I just came in for lunch and saw that I had received your response.

You nailed it -- it is a leak in the system. Specifically, there is a suction hose (see #2 below) that takes in the large cooling-system-sized flow of oil from the sump and distributes it to both of the pumps -- it had about an inch crack (which followed the hose mold as seen in the picture) on the back side of it. That explained the "drip-drip-drip" leak of oil which led me to the problem -- the crack was probably also sucking vast quantities of air (in a hydraulic sense), causing the impaired flow to both pumps -- which initially led me to conclude that the problem was common to both pumps -- meaning that it was probably not a relief valve issue.

My local dealer doesn't have the hose (item #2 below; part number M136804), so I will expedite order it on Monday. Actually, I'm going to order two of them -- they are just $14.50 each -- and this is a part that can definitely lock you down wherever you are with your tractor, so the extra one is cheap insurance.