i need a hydraulic pro diagnosis, 334D

   / i need a hydraulic pro diagnosis, 334D #1  

outfront

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Dec 24, 2020
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Tractor
bobcat 334d
Im new here is this where i would post a difficult hydraulic question about my 334D?
 
   / i need a hydraulic pro diagnosis, 334D #2  
Right here I sure somebody will help....So what's the problem?...
 
   / i need a hydraulic pro diagnosis, 334D
  • Thread Starter
#3  
2004 334D owned for 8 years flawless,

one day worked great the next morning almost no travel from both sides, swing boom poor and main boom down all super weak. however if you load the system like topping up the backfill blade pressure goes up to 3000psi and the travel, swing boom and main boom down work at about 50-60% on the control valve assembly it is the first four valves that are affected. fluid is clean, and i have now used it for 2 months for digging with no issues so far.

(left travel, swing boom, main boom and right travel). the main boom up seems not affected because i think there is a booster valve that helps this function. i got a schematic but there are so many possibilities. the pump is an internally regulated 3 port (one gear and 2 piston pumps) the gear section does the main hydraulics, the piston pumps do the travel and swing boom and main boom operations. there are three main by-passes on the unit and they are set at approx the same setting so i removed all three and tried them in different positions to see if problem moved--it did not and i returned them to their respective spots. i dont know if that is a good or productive test. if one was bad would the results be the same in any position?

i am a mechanic by trade, an automotive shop owner so i know wrenching but this is a little over my head. there are some port relief tests i can do where i manually pump fluid into the valve blocks to see when valve opens but not sure these test would whelp in this diagnostic

i did do a n aux test with a pressure/flow meter and got 14gpm @ 900 psi at high idle and 12gpm @ 800psi at med rpm and 10 gpm @ 600 psi near idle if this helps but per the diagram the aux is probably mostly driven off the gear section of the pump. my flow meter is have does not have a restricting valve to load the pump like the manual asks for
 
   / i need a hydraulic pro diagnosis, 334D #4  
I suspect the Load Sense signal (line from control valve to piston pump) is not getting to the pump to bring it on stroke completely. On the side of the piston pump is a small valve block with 2 small lines connected 1 is the hose from the main control valve the other is case drain line back to tank. Inside that valve is a spool that moves with pressure to bring the piston pump on stroke or destroke as needed, that spool has a small orifice and if blocked or partially blocked pump will not stroke correctly.
 
 
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