656 Hydro won't move update

Bill in IL

Well-known Member
I was able to get into the hydro this evening. Both the high pressure lines look fine and the check valves were both closed and seemed to my untrained eye to be ok. I could compress the valves with a screwdriver and they sprung back into place effortlessly. The only noteworthy thing is the forward check valve was torqued very tight.

I have not put oil back in it yet but assuming there will be no change. Anyone have anymore good ideas?
 
this maybe a dum question but are you sure the range lever is moveing gears? is it a possibility that a roll pin is broke somewere? maybe the shift fork? just a thought
 
First off, is the "clutch disc" or "driver plate" attached to the flywheel intact and actually driving the hydro pump?
 
(quoted from post at 21:08:23 07/28/14) First off, is the "clutch disc" or "driver plate" attached to the flywheel intact and actually driving the hydro pump?

In the original post Bill stated the tractor had control pressure, steering, PTO and other hydraulic functions.

Bill, have you checked the shuttle valve to make sure it is not sticking?
 
I have thought that myself. When I move the lever it does have resistance so I am assuming that yes it is going in gear.
 
One possibility is that one of the relief valves was stuck open and when loosening it it became free and closed. The manual recommends that you stick a small wire in through the fitting after removing the pipe to measure the distance to the piston and then compare that dimension after the valve is removed.

The most common failure of one of the jumper tubes attached to the relief valves is for them to crack on the end under the sleeve. That is not going to be your problem since a cracked line will not keep the tractor from moving at all but instead will cause the hydro to slip at too low a pressure.

One way to check if there is any movement of the hydro motor is to engage the hydro with the range transmission in neutral and the shift to either high or low range and see if there is any gear clash.

Capping the two lines as the exit the hydro housing if the best way to determine if the problem is inside the hydro housing or an external control problem.
 
I even checked again this morning I can hear it going into gear when changing the gear shif lever.

Yes this tractor does have functional hydraulics, PTO and steering.

I was reading in the archives and a test that was suggested was capping the 2 high pressure lines going into the transmission on the left side of the transmission. It was suppose to isolate the control valve from the internals of the transmission. I did that and it still did nothing.

Now after removing the relief valves I question if that is a valid test. Those 2 small lines are suppose to provide pressure to the relief valves via the control valve right? How does the high pressure get up to the control valve?

I would like to try and figure out from the foldouts but the manual i have is a reprint and they butchered the foldouts to standard size paper... very frustrating to look at.
 
The two lines are internally connected to the forward and reverse high pressure relief valves. The relief valves are pilot operated. That means the pressure setting is controlled by the Foot-N-Inch (clutch) valve and not the valves themselves. That is why you can easily move the valve piston when your finger. There is a small hole in the end of the piston in the valve. That allows the hydrostatic pressure to be equal on both sides of the piston so that the spring in the valve can keep it closed. The oil that passes through the hole in the valve is connected by the tubes to the Foot-N-Inch where there is a valve connected to the pedal. That valve is set to open at about 5000 psi. When the Foot-N-Inch valve opens it dumps the oil that passes through the relief valves and causes an imbalance in the relief valves which causes the pistons to move and dump the hydro oil from the hydro motor. Since both valves are connected together at the Foot-N-Inch valve, if either valve is stuck open the tractor will not move in either direction. Capping the lines coming out of the housing will cause the relief valve to not open since they will have pressure on both sides of the piston.
 
Thanks for the great description of how the relif valves work. Later I will take apart my book and lay out the diagrams so I can look at the whole picture of what you are talking about.

Yes I see in the manual where it says to put a wire in the valve. It was a case of I had no idea what I was looking at or for till I had it out and in my hand. I was wondering since it stresses in the manual to not overtorque the valves if that was the problem. I am assuming though that once the vales are overtorqued they are ruined and will always cause problems?

When you cap the lines at the housing should that be done one at a time or both at the same time. When I did it it was both at the same time.

Looks like my next step is to put it back together and refill the oil and try it again since it may have been the forward relief valve being overtorqued.
 
I have a 656 hydro and think they are a great tractor. With charge and servo pressure being good I would look at the range shifter. On mine there is a definite "clunk" at each end of the stroke. My range shifter was seized when I bought it and took a fair bit of work to free it. The linkage comes down just in front of the steering pedistal and then rearward under the battery to the case. You can see if it is moving by removing the battery plate or the platform.
 
Since you said you had charge pressure here is some things more to consider. This assumes that the problem is internal which can be verified by capping the external lines.

Along with the two high pressure relief valves the center section on the hydro unit also contains a forward check valve, a reverse check valve, and a shuttle valve. When the hydro control lever is moved and the motor starts to develop pressure the check valve for the direction the tractor is set to go in closes and the shuttle valve moves to allow make up charge oil to enter the hydro loop through the other check valve. Failure of either check valve can also cause the tractor not to move. The shuttle valve is know to have problems with the snap ring on the left end coming off. When that happens the spring will no longer center the valve. That problem also will cause the tractor to have no forward movement after using the Foot-N-Inch valve or if the hydro has slowed the tractor while moving forward. Reverse will still work and the tractor will again move forward if you first go into reverse and then go forward without using the Foot-N-inch pedal.

Another thing that can happen is a failure of the servo control cylinders. I have seen broken lower pivot holes. Also make sure the control rod coming from the speed control handle is still connected inside and is actually moving the cam.
 

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