I'm looking a t buying JD 490E It has a Hydraulic problem, the boom and stick are jerky " not smooth". and when you put the boom down slowly it seem to fall to fast. Not sure what that might be, any ideas? The owner say the main control valve is bad, that's $13k part, it sits behind the boom. The only reason i'm considering the it's in great shape other wise, 5,000hrs. strait, good under carriage wide pads. for only $8,000, price is right. Any ideas. thanks
Sounds like the price is right. Diagnostics at a distance with no schematic is more of a WAG than anything else. Jerky operation as well as the boom lowering rapidly could be nothing more than air in the circuits. It probably would be wise on your part to spend the money for a professional to help you get this worked out, provided you buy the machine. Good luck, Maytag
Yes I thought about air in the system. My father inlaw is a heavy equipment mechanic for over 30 years. so he's my help. Just whated to see if anyone else ever ran in to the same problem with a JD or Hitachi. thanks
If you have the opportunity disconnect and put a pressure gauge in the boom down pilot line at the control valve .Do not reconnect line to the control valve. observe the pressure gauge while working the boom lower pilot lever. You should be able to control the pressure very smoothly between about 140 PSI and 400 PSI. If it is not controllable your problem is pilot pressure related. Try the same procedure on a function that seems to be very smooth to control and compare the results.