Cat Lift Trucks (& Caterpillar) DP40KL:
slow hydraulics

i am working on a Cat DP40KL the truck has had slow/weak hydraulics it happened about 6 month ago good pressure input to the spool valve assembly. replaced main pressure relief valve and issues were resolved. about a month ago the truck lost full hydraulics pump seals were blown pump was replaced and hydraulic service was done. about a week ago the truck started to have slow and weak lift again adjusted main relief valve no change swapped out valve still have issues swapped out spool valves and still have the issues. all mast functions are effected steering is good but to use lift,tilt or side shift you have to floor it and still moves slow truck is a 9000lb capacity and will barley lift 4000lb right now. any ideas of where to go would be great help.
  • Posted 22 May 2016 16:34
  • Discussion started by kacey_t
  • Colorado, United States
Showing items 1 - 7 of 7 results.
that valve on the front that feeds the two main cylinders is the flow regulator valve. All this valve does is regulate the lowering rate of the mast lift cylinder(s).

After doing some more reading in the service material all the flow priority is handled in the 'inlet' section of the main control valve. It contains the 'flow priority valve spool', main relief valve, and steering relief valve.
The flow priority valve is part of the inlet cover itself, the cartridge is under a big hex plug/cap on the front of it that you remove and the spool and springs are inside that cavity. Then of course the main pressure relief valve is the one on the top side of the inlet cover and the steering relief valve is the one on the under side.

that flow priority valve should move freely and any springs should be intact.
  • Posted 24 May 2016 10:48
  • Reply by swoop223
  • North Carolina, United States
You've been swooped!
Thank you for the help I am going to check the systems pressures today. One thing I was wondering mounted on the front of the truck there is a large valve body that feeds the two main lift cylinders what is that?
  • Posted 23 May 2016 22:20
  • Reply by kacey_t
  • Colorado, United States
come to think of it kacey that is correct, i was thinking of another system that has the (flow divider), steering priority valve separate. On this truck the system handles that differently, all contained in the control valve itself.

now after looking in the troubleshooting guide for slow lift and tilt it does say to check and/or change the relief valve which you have done, but it also says that there could be the relief valve setting set too low, it should be set to relief at 2750psi. Also says there could be a faulty oring on relief valve body.
And last it says to check the control lever adjustment on the spool stroke, make sure you are getting a full stroke when pulling the lever.

also i would check the tank strainer (inside the tank), another section mentions this as a possibility if lifting speed is too slow.
  • Posted 23 May 2016 20:48
  • Modified 23 May 2016 20:50 by poster
  • Reply by swoop223
  • North Carolina, United States
You've been swooped!
the flow divider valve is located in the valve body next to the lift spool valve correct?
  • Posted 23 May 2016 15:10
  • Reply by kacey_t
  • Colorado, United States
check the safety valve in the main cylinder inlet fitting
you also may want to check the flow divider valve
  • Posted 23 May 2016 14:34
  • Reply by swoop223
  • North Carolina, United States
You've been swooped!
From the local cat dealer OEM replacement.
  • Posted 23 May 2016 09:07
  • Reply by kacey_t
  • Colorado, United States
were did u get the new pump ?
  • Posted 22 May 2016 21:10
  • Reply by DAMO
  • DUBLIN, Ireland

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