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1986 c30 roll back tow truck blowing the seals out the hydraulic

Discussion in 'Trucks' started by Tomcat955, Jun 9, 2022.

  1. Tomcat955

    Tomcat955 Member

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    Sep 12, 2021
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    Location:
    Illinois
    Hey I’ve got a old c30 roll back tow truck. Seems like whenever the bed bottoms out it blows the seal clean out the rear of the hydraulic. We tried repacking it twice and every-time it over pressurized and boom goes the seal and bushing right out the back. Any idea what could be causing this? View attachment 261374 View attachment 261375
     
  2. Coaldust

    Coaldust Senior Member

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    Cargo Tanks, ULSD, RUG, Methanol, LPG
    Location:
    North of the 60
    Welcome.

    I’d be inclined to check the main relief valve pressure.
     
  3. Tomcat955

    Tomcat955 Member

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    Thanks Coaldust. Do you know where these would generally be found or what they look like? I’d imagine ited be a valve to dump back into the tank before the valve body. The main valve body had a couple of what looked like relief valves we took apart and cleaned no dice still blew it apart. Is there a set of gauges I can buy and plumb into the system to check pressure? I’m not new to mechanics but This is my first time doing serious diagnosis work on hydraulic systems I appreciate the help.
     
  4. Coaldust

    Coaldust Senior Member

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    No problem. Couple things you could do.
    Does the pump have a tag on it? You could go to either the Chelsea or Muncie website to look at the manual for it. But, the main relief will be on the pump. It may or may not be adjustable.

    To check the pressure, you could attach a 3000 psi gauge to the hose that goes to the head end of the cylinder that keeps blowing. Report back.

    What’s the pressure supposed to be? IDK.
    Probably in the 1250-1500psi range.
     
    Jonas302 likes this.
  5. Tomcat955

    Tomcat955 Member

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    So I pulled apart the truck again today am I missing a lock ring or circlip? I couldent find a pressure gauge to check the pressure but it really seems like there’s nothing there stopping it from shooting out the bushing other then the press fit seal. Maybe the last owner lost the lock ring and just peened the brass edge over

     

    Attached Files:

  6. heymccall

    heymccall Senior Member

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    Show picture of whole pump.
    Is it shaft driven or on pto?
    What color is it?
    Any tags or ID anywhere on it?
     
  7. Coaldust

    Coaldust Senior Member

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    The lock ring is missing. Doesn’t look like there is enough groove left to hold a lock ring. IDK? Might be able to purchase a new head for it. Or, machine and install a dowel pin through the head and bushing. Install a quality wiper seal.
     
  8. Tomcat955

    Tomcat955 Member

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    The pump is mounted on the side of a sm465 I think there needs to be a lock ring of some sorts I may use a lathe and cut a groove and stick a pin or something in there to keep the bushing in place.
     

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  9. RoanokeMassey

    RoanokeMassey Member

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    Indiana
    You need a way to lock it in.
    However is this a one way or 2 way plumbed cylinder? If it's just getting oil on one end, then the other end needs a vent. There are vents that have wire mesh in them to stop thing entering the plug hole or some installers make their own vents by drilling a small hole in the plug. Like grain trucks end dump trailers they only have one way plumbed cylinders. But if the cylinder leaks internal then oil gets on the other side of the cylinder and it must vent somewhere or blow the seal. I have seen guys replace a vent plug with a sealed plug and have problems. My first guess is you are missing a locking clip. New cylinders are not that pricy, if you avoid someone from getting burnt by oil or some one trusting the cylinder and having the bed come down on someone.
    If it can not be fixed correctly, I would buy a new one.
    Since you are new to hydraulics.
    Never ever use galvanized pipe fittings on hydraulic pressure lines. They are not close to being rated for hydraulic pressure. Black iron pipe fittings can be used. But it is best to get regular hydraulic fittings, yes they cost more, but they are rated for hydraulic pressure, not house hold plumbing.
    I am an old farmer and I have seen, lots of make shift repairs that scare me. .