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Cat 235 swing motor

rush ยท 2011-12-30 12:30

I am hoping there is someone out there who knows something about the old style piston type drive and swing motors for the old CAT 235 excavator. The swing motor on my old machine is very weak and whole machine swings down hill on its own unless the manual swing brake is engages. I am wondering if the problem is with the swing motor, hyd pump, or maybe even a worn out or stuck relief valve. I have the parts manual which is basically useless and is very confusing. Any help would be appreciated. Thanks Rush

Replies6
  1. #1DIRTROAD2011-12-30 13:37

    You could try calling this guy: http://www.upstatehydraulicdesign.com/ He is pretty knowledgable and easy to talk to.

  2. #2garp2011-12-31 00:21

    find your swing relief and combiner valve. follow your lines off the motor to the valve, should be right ahead of the motor towards the boom. could be a worn seat or bad springs. relief is 2350 psi. springs should measure around 3.25 in.

  3. #3rush2011-12-31 20:25

    Thanks for the input. i will check the relief first. Is the relief valve located in the combiner valve body? BTW, do you happen to know what the purpose of the combiner valve is? Thanks Rush

  4. #4garp2011-12-31 22:30

    Yes, the relief is located in this valve body. The combiner valve acts so that one relief can control both sides of that circuit.

  5. #5rush2012-01-01 21:13

    Garp Thanks for the info. I took the PR valve off today and found that the first stage plunger with all the holes drilled in it was stuck open. I took it all apart, cleaned it out, and used some penetrating oil to lube all the parts up so that everything worked nice and smooth. I haven't had a chance to check out how the swing motor works now, but I am thinking that was at least part of the problem. I will let you know how it works once I get all the hyd oil put back in. I had to drain out all the hyd oil because it was all milky because of water in the oil - such a pain in the neck. I am sure that what caused the PR valve plunger getting stuck open. Not sure I will ever be able to get it all cleaned up. It turns out that if you heat up the milky oil and boil off the water the hyd oil turns back into the honey colored clean hyd oil it used to be. I will take a few batches of heating the oil up, but is better than buying 190 gallons of new hyd oil at $10/gal. Thanks for the help

  6. #6garp2012-01-02 01:10

    Sounds like you are on the right track.