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1995 Lull 644TT

Douglashd16b ยท 2025-10-19 21:58

Good Afternoon everyone, I bought a1995 Lull 644 last year to use on the farm and it has a hydraulic issue I cannot seem to figure it out, I know alot good mechanics are on here. My problem is one of my stages on the dual pump is constantly loading the pump up and if I use it for any period of time the oil will heat up so bad that you can't touch the tank.when it does this I have no pilot pressure so the machine is dead until It cools off. This is a control manifold hydraulic machine. Any help is greatly appreciated

Replies15
  1. #1Vetech632025-10-20 09:03

    Some pics of your pump and control valve system would help.

  2. #2tractormech2025-10-20 18:42

    Whats the model and serial number. You have a somethong bypassing causin the oil to heat up

  3. #3Douglashd16b2025-10-20 23:23
  4. #4Douglashd16b2025-10-20 23:24

    1995 644TT-34

  5. #5Douglashd16b2025-10-29 10:23
  6. #6Douglashd16b2025-10-29 10:24

    This is where the hissing is coming from and I can feel it getting hot there

  7. #7Vetech632025-10-29 10:25

    That looks similar to a thermal bypass valve but I can't see where the lines are running.

  8. #8tractormech2025-10-29 11:03

    Is that the foot brake valve?

  9. #9Douglashd16b2025-10-29 12:44

    That is the pump unloader valve, I just took it all apart and all seems fine

  10. #10Douglashd16b2025-10-29 13:27

    I'm sorry,I was wrong, this is the Accumulator charge valve. I need one,anyone know where I can get one. PN. P28728. Thanks in Advance

  11. #11B&B2025-10-30 00:22

    Web equipment out of virginia should be able to help. I was recharging an accumulator on a lull and had questions on the pressures and they were more than happy to walk me through how they do it and gave me any info I could need.

  12. #12Douglashd16b2025-10-30 05:16

    Already tried Web, they don't have one

  13. #13Douglashd16b2025-12-03 19:42

    Guys, I found a used valve by chance, put it on and have the same problem. Boy I thought I had it. I have a question for those that are familiar with these machines, Am I suppose to have pressure with the engine running and no functions activated. I ask because one section of the the dual pump only has pressure when I turn the steering wheel, the other section which is the one that I am having problems with will build to 1900 psi and kick out then immediately load up and start again and yes I have 450 accumulator charge. Any help would be much appreciated

  14. #14Douglashd16b2026-01-04 23:28
  15. #15Douglashd16b2026-01-04 23:30

    Update, I changed this valve [ called brake port block] and it fixed my problem