743B forward drive on right side quits working, Ideas??

[crash66749_in_sek]

I am working on a friends 743B. The controls are jerky but I somwhat expect that on an older machine. The forward drive on the right side works for the first minute or so then begins to quit working on it, every now and then it will lung if you hold the right handle forward but that is it. Rear drive on the right side works great as well as the left side drive forward/back work great. I can't believe it is the hydraulic pump, it seems like it is in the controls. Any ideas are welcomed. Thanks.

 

[Tazza]

There is no reason for the controls to jerk around, I'd start by checking the linkages at the steering levers and the pump. They run rubber bonded to steel and the rubber does break down. If you have good power on both sides in one direction I'd agree the pump seems to be ok as the same rotating group generates pressure for forward and reverse. The only causes i can see is the high pressure relief valves or seals in the motors.
The motors also have shuttle valves, yours could be a little sticky causing problems.

 

[crash66749_in_sek]

There is no reason for the controls to jerk around, I'd start by checking the linkages at the steering levers and the pump. They run rubber bonded to steel and the rubber does break down. If you have good power on both sides in one direction I'd agree the pump seems to be ok as the same rotating group generates pressure for forward and reverse. The only causes i can see is the high pressure relief valves or seals in the motors.
The motors also have shuttle valves, yours could be a little sticky causing problems.

The service manual I have lists the high pressure replenishing valves as a possible culprit (I would guess they are the relief valves you speak of) The picture is so vague in the manual. I unscrewed the two caps on the right side of the block above hte hydrualic pump and took the valves and springs out of the bores and inspected them. They had some pitting which if they are running up to 3000psi they wouldn't be totally seal off. Were these the relief valves you are talking about? They looked different from each other. If it is a shuttle valve in the motor, should I buy a new motor or have it rebuilt to fix something like that?

 

[Tazza]

The service manual I have lists the high pressure replenishing valves as a possible culprit (I would guess they are the relief valves you speak of) The picture is so vague in the manual. I unscrewed the two caps on the right side of the block above hte hydrualic pump and took the valves and springs out of the bores and inspected them. They had some pitting which if they are running up to 3000psi they wouldn't be totally seal off. Were these the relief valves you are talking about? They looked different from each other. If it is a shuttle valve in the motor, should I buy a new motor or have it rebuilt to fix something like that?

The relief and replenishing valves are different i believe, the replenishing valve allows fresh oil in but holds high pressure oil in the system when you are driving. Minor pitting shouldn't be a problem. There are more than 2 valves, there should be 2 on either side, naturally there are 2 behind the bar thats used to centre the pump!
The motors you can re-kit your self, much cheaper than a new one!

 

[OldMachinist]

The relief and replenishing valves are different i believe, the replenishing valve allows fresh oil in but holds high pressure oil in the system when you are driving. Minor pitting shouldn't be a problem. There are more than 2 valves, there should be 2 on either side, naturally there are 2 behind the bar thats used to centre the pump!
The motors you can re-kit your self, much cheaper than a new one!

If I read your first post correctly your saying that on the right side the front wheel is working different than the back wheel? If thats correct then it sounds like a drive chain problem as they both work off the same motor.

 

[Wolf88]

Check the drive case under the park brake lever. You will need to remove the cover just under the pump its a bit tricky but it can be done. Look to see if the chain drive sproket is loose. The axle that the two chains front and rear are looped over . See if there is any movement up and down . Compare it to the left side. Mine just died, the bearings collapsed and went thru the drive and damaged the chains and crunched the drive shaft. Did some damage to the drive motor also (Hydraulic) costing me heaps to fix and could have been avoided had I had a clue like yours. Mine just stopped on the left side, right side works ok. Will try and post some pics later if I can. cheers Wolf 88 from Australia

 

[bobcatbros]

We had a similar problem with an M700. Turned out the yoke was worn out where one of the shafts go in the hydro motor.