721 drive problem

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windy22

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Jun 21, 2007
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My 721 has a problem when driving slow forward it often start to go backwards at the right hand side. Then the directions are mixed up, moving right lever forward will make right side run backward and if I pull the lever backward it will make the right side go forward !? If I go slow again the direction shift to ok again. As long as I pull the lever firmly forward then no problem occurs. Both sides always has god drive power, even when the direction is messed up at the right side. I think hydraulic motor/pump is quite soundy when driving. I have read something about a bronze filter on some models, is it a filter like that on 721 and if it is, where is it located on this model? Maybe a clogged bronze filter is my problem? Any other suggestions?
 

Tazza

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To me it sounds like loose linkages to the hydrostatic pump. I do take it that this model is hydrostatic drive and not belt or clutch?
Start by checking the linkages from the levers all the way to the pump and see if they seem tight.
The bronze filter is only a problem with causing lack of drive, it will cause a lot of noise and little power. It shouldn't cause this issue....
The only other thing i can think of is the valve plate in the motor may be out of time. Has it always had this problem? and have you opened the drive motor? They need to be put together in a set position or dirive direction may be reversed.
The bronze filter if you have one will be located in a square block on the hydraulic pump. There should be 3 hoses on the left, its behind the middle one. Remove the hose and fitting to gain access. This is me assuming it runs a vickers TA1919 pump like most of the early 7 series machines.
 

windy22

New member
Joined
Jun 21, 2007
Messages
2
To me it sounds like loose linkages to the hydrostatic pump. I do take it that this model is hydrostatic drive and not belt or clutch?
Start by checking the linkages from the levers all the way to the pump and see if they seem tight.
The bronze filter is only a problem with causing lack of drive, it will cause a lot of noise and little power. It shouldn't cause this issue....
The only other thing i can think of is the valve plate in the motor may be out of time. Has it always had this problem? and have you opened the drive motor? They need to be put together in a set position or dirive direction may be reversed.
The bronze filter if you have one will be located in a square block on the hydraulic pump. There should be 3 hoses on the left, its behind the middle one. Remove the hose and fitting to gain access. This is me assuming it runs a vickers TA1919 pump like most of the early 7 series machines.
The linkage to hydrostatic pump looks fine without any unusual slack. I was thinking that a clogged filter causing cavitation make the pump or motor going nuts. At the time when motor suddenly changes direction drive get noisier. Is it really possible that the drive motor somtimes get in the right direction och other times in wrong direction if it has been put together in wrong position. I havent yet opened the motor and/or pumps yet, I made post here first to see if anyone had similar problems.
 

Tazza

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16,697
The linkage to hydrostatic pump looks fine without any unusual slack. I was thinking that a clogged filter causing cavitation make the pump or motor going nuts. At the time when motor suddenly changes direction drive get noisier. Is it really possible that the drive motor somtimes get in the right direction och other times in wrong direction if it has been put together in wrong position. I havent yet opened the motor and/or pumps yet, I made post here first to see if anyone had similar problems.
The only way to know if it is the motor for sure is to swap the motors over. I'm not sure if they are bolted into the chain case from the inside though. If you remove the hydro lines and the 4 bolts it *should* slide out. If you can do this and the problem goes to the other side your motor is out of time or you have a problem with the valve plate.
I can't see cavitation causing this problem, it usually causes lack of power and a LOT of heat and noise.
 
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