720 drive issues

[sonnyyar]

Any suggestions would be appreciated. Both sides of the drive system are extremely loud with little movement in forward/rev. The lift hydraulics are working fine. After a few minutes of running, the hydraulic oil becomes foamy. I've replaced the fluids and both filters, but it didn't help. To reduce the possibility of leaks on the suction side, I temporarily piped the suction side of the hydraulic pump straight from the tank, but it didn't help. I've installed a gauge on the hydrostatic filter and read approx. 20 psi until I attempt to move for/rev. and the gauge goes to 0-5 psi. I'm obviously "starving the hydrostatic part of the system, but not sure where or why. Thought of changing relief valves and bypass valves but didn't want to just blindly throw money at the problem Thanks in advance for help. I may be a few days before I can get back on the problem.

 

[Tazza]

You mention BOTH filters, you replaced the bronze one on the inlet side of the pump? I'm assuming you have a vickers TA1919 pump. If so, there will be a square block on the top of the hydraulic pump. Left hand side, middle hose. Remove the hose and the fitting that screws into the block, there is a hidden filter here that causes the EXACT problems you describe.
I hope thats it, it was the problem i had on my 731.

 

[sonnyyar]

You mention BOTH filters, you replaced the bronze one on the inlet side of the pump? I'm assuming you have a vickers TA1919 pump. If so, there will be a square block on the top of the hydraulic pump. Left hand side, middle hose. Remove the hose and the fitting that screws into the block, there is a hidden filter here that causes the EXACT problems you describe.
I hope thats it, it was the problem i had on my 731.

Thanks for th quick reply. I'll check that out. I have the service manual for the 720 and 731 and see the bronze filter on the 731 that you're talking about. I think the 720 only has 2 external filters. One lager filter after the oil cooler before it dumps back into the tank and 1 small (the size of a typical car oil filter) at the entrance of the hydrostatic pump. Again, I appreciate your help and will check it out..

 

[sterlclan]

Thanks for th quick reply. I'll check that out. I have the service manual for the 720 and 731 and see the bronze filter on the 731 that you're talking about. I think the 720 only has 2 external filters. One lager filter after the oil cooler before it dumps back into the tank and 1 small (the size of a typical car oil filter) at the entrance of the hydrostatic pump. Again, I appreciate your help and will check it out..

It kind of sounds like my machine acted(same pumps).....the wear plates in the pump could be getting worn not too tough to repair or replace it was worse getting the pump out...Tazza has some good pics of the inside of a pump and all the info is readily available online good luck......Jeff