631 Drive power

[travis ledger]

Hi All, I have an old 631 with a drive problem. It is fine when the machine is cold but after about 20min of use it start's to lose power when driving so much so it will not even skid steer on grass or soft dirt. I have replaced the main hyd filter, checked and cleaned the sintered bronze filter (middle hose left side of the block) is this the only filter I should check/clean? could it be a relief valve problem?, on what part of the system would I check the hyd pressure and what should it be? The lifting hyd still work fine. Thanks for any help

 

[antfarmer2]

What kind of fluid?............does it have drain case filters?............is the oil cooler and radiator pluged with crap?..........how long has it been doing this and did it come on fast or slowly

 

[Tazza]

What kind of fluid?............does it have drain case filters?............is the oil cooler and radiator pluged with crap?..........how long has it been doing this and did it come on fast or slowly

No case drain on this machine, goad you got the hidden filter, how well did you clean it? i found taht i cleaned mine and it still wasn't quite rite, second more thorough clean and it was good to go. Even try running it without the filter and see if the problem still exists. It sounds a LOT like a suction line blockage.
You still have your main hydraulic filter, but that is easily seen.
It could be the fluid, but depending on how bad it gets, it could be pump/motor wear.
After it has stopped working, check the oil, is it foamy?