1974 Satoh Bison weak hydraulics

Chemgeek · May 5, 2015

I have a 1974 Satoh Bison 650G. The engine runs great. The problem is the hydraulics.

The hydraulics worked fine. Then, I replaced two leaking hoses to a front end loader and lost power. I can lift the bucket to a certain point and then it stops. The lift arms go up without a load, but if I stand on them, the arms don't move.

I've checked all of the obvious issues based on conversations I've had on and offline (BTW, I'm a hydraulic novice). There's plenty of fluid. The pump is pumping the fluid. I cleaned the filter screen (which wasn't dirty). I've fiddled with everything.

Here's where I'm at:
I disconnected the FEL and isolated the fluid reservoir and lift arms. I took the cover off of the reservoir and saw the fluid is pumping into the reservoir from the pump. When I pull back the lift arm controller, fluid is diverted to the lift arms as it should be. But the arms (when weighted down with a pair of cinder blocks) don't move more than an inch.

Here's the interesting part. When the tractor is cold and I first start it, the hydraulics work just like they should for about a minute. After that minute the lifting power fades away. I did that tonight and tried 2 hours later and same thing happened.

So, I'm stumped and that's why I'm here. Any ideas?

J_J · May 5, 2015

Hydraulic System: 650G

Type:

One Cylinder
Pressure of Relief Valve Setting:

1365 +/- 71.10 lb/in^2 (115 +/- 5 kg/cm^2)
Maximum Lift Power at Lower Link:

1,102.5 lb (500kg)
Diameter of Ram Piston:

2.76 in (70mm)
Stroke of Ram Piston:

3.15 in (80mm)
Material of Ram Piston:

Cast Iron FC-25
Type of Hydraulic Pump:

Pressure Loading Type
Name and Model of Hydraulic Pump:

KAYABA-DOWTY, GP-1
Output of Hydraulic Pump:

4.1 gal/min (17 ltr/min) @2800 engine rpm
Control Valve (Height Control):

Spool Valve, Pilot Type
Lock Valve:

In-line Non-return Valve (Automatic Flow Control)
Control Valve (Sub-Control):

Spoool Valve, 3-way Flow Change Type
Strainer Mesh:

100 meshes
Hydraulic Oil:

Turbine Oil No 120 (Capacity .92 gal - 3.5 lit)

Can you install a pressure gauge in the hyd circuit and check the pressure when you raise the lever?

Your 3pt relief pressure is 1365 psi.

When you have the FEL installed, the FEL will set the relief for the system.

The cyl should be filling when you raise the lever, and when full will dump pump flow through the relief valve. .

Is the fluid dumping into the reservoir when you raise the lever?

Chemgeek · May 5, 2015

JJ,

I don't have a pressure gauge. So I can't get that data.

The FEL is completely disconnected right now as I troubleshoot. I can physically push the lift arms get to the up position. When they are completely up, fluid is diverted back to the reservoir, which I assume is how it should be. But, the hydraulics on their own can't lift them (except during the first 30 seconds after a cold start).

J_J · May 5, 2015

Then, what you need is a flow and pressure test at the dealer to test the pump.

When the FEL was installed, did the FEL have good hyd.

KGauger · May 7, 2015

I am having the same problem with my Bison. One of the original hoses busted spraying fluid everywhere, no FEL. I shut off the tractor. I had to go to several hydraulic shops to find the correct ends and get a replacement hose. Replaced the hose and added fluid to the reservoir under the seat. Since then, the back lift has not worked properly. As you started, the lift will work some when you first start the tractor but will not work after I lower the rotary cutter and try to raise the rotary cutter again. And the hydraulic pump has made a noise at times. Does the pump need to be bleed? I am a complete novice in this case.