Wrecker Hydraulic issues

[brianrbull]

Ok so I come home on leave to play with my new toys....one of which is a M816 from Indiana decent truck but in need of a little love, Cables birds nested, no heater, somone turned the engine down so it hits the governer at 2000 RPM...nothing too serious but the hydraulics dont hold the boom creeps down fairly fast . I thought it might be air in the system but the hydraulic tank is full and I have run it up and down 50 or so times thinking that might fix it. I am now thinking that it must be a stuck check valve allowing the boom weight to push the oil back into the tank. I can see no leaks at any hoses,valves and the cylinder packings are dry . am I correct in assuming that there is a check valve of some sort? and if so can anyone tell me where it is located? Thanks

 

[papercu]

You can check TM 9-2320-260-34-2 it's on this site for download. Search for "check valve". Also Kenny has a manual for the wrecker body on here not sure what it covers. Wayne

 

[54reo]

There is a "creep test" part of the annual load teat required on all equipment that is to handle ordinance. The point being, it tells you how to diagnose and correct the problem you are speaking of.

It is in one of the M809 TM's.

 

[4052]

It probably is one of the boom cylinder piston seals by-passing oil.

 

[rosco]

It probably is one of the boom cylinder piston seals by-passing oil.

Or it can be a control valve, leaking around the spool. Sometimes things just wear out, or worse, foreign material (metal) gets into the system and causes the packing to wear or gaulding the cylinders. Sometimes you can put your ear next to the cylinder & hear it leaking by.

Lee in Alaska

 

[jrou111]

First of all, we need some pics Second, you need to remember that working on hydraulics is dangerous, Kendelrio(sp?) posted a good safety guide on it a couple of weeks ago. Third, good luck with your issue and let us know what you found!

 

[brianrbull]

I am not home right now to work on the beast, but correct me if I am wrong but if it was a leaking cylinder packing would it not be venting oil(Leaking) outside?

 

[ncduece]

no it would just leak by internally from pressure side to return side

 

[NDT]

It probably is one of the boom cylinder piston seals by-passing oil.

My vote . . . repacking the cylinder is what fixed this problem on my track hoe.

 

[Stretch44875]

Just had this problem on a man/boom lift, it was bad internal packing. That being said, I would check the easy stuff first. I think that is a garwood crane on the truck? Kenny's manual is for the austin/western cranes. Need a hydraulic diagram/schematic to be of any help. It could be a load check valve leaking, not sure if they use one.

Dennis

 

[zb39]

Welcome home and good luck!

 

[brianrbull]

Here is another thought I have , if it is a leaking packing would it not just tip to the side with the leak? as it has 2 cylinders? just a thought I wont be able to do anything with her till Aug when I go on leave. Thanks for all the help and keep the Ideas comming

 

[gimpyrobb]

No, rather large pins going through the metal. I know a guy that was missing the passenger side piston all together, crane still worked just at a reduced capacity.

 

[brianrbull]

I guess let me clarify my thought, I realize that the boom would not "Tip" that far but if one packing was leaking would that cause the other to also "Bleed Down"?

 

[gimpyrobb]

Thats why Stretch was talking about a hydraulic flow schematic. The cyls could be tied together in one circuit and one bleeding will cause a drop in pressure in both(most likley the case) or they could be set up individually(I doubt it). Does that make sence?

 

[brianrbull]

Yes that makes sense I am checking the TM now......any ideas on where packings for the cylinders could be sourced?

 

[brianrbull]

Well I have scoured the TM's I cannot find a Hydraulic Schematic, I did however find that there is a check valve installed in the bottom of the lift cylinders, TM 9-2320-260-34-2 Page 487 Item 20
I am having a hard time finding the corresponding part in the 34p manual.....

 

[gimpyrobb]

I might have some packing. I got a lot out of Indy that was left over from a wrecker rebuild program(lots of seals and felt). If you can find an nsn, I might be able to match it up with something I have in a "big box".

 

[brianrbull]

So ok I think I have found the Check Valve Part #'s
TM 9-2320-260-34p-2 Page 353 items 8,9
Both are 90 degree JIC-Male-Female 90 same dimensional data, # 9 varies from # 8 in that 9 has a pipe plug in it and is 3x the cost I am assuming that #9 is the check valve? (Assumption being the Mother of all...Well you know) Any one have an opinion on this?

 

[Ferroequinologist]

I built cylinder tester when I worked at the steel mill, we would have major hydraulic issues on everything.
It was just a 1in ball valve (3000psi rated) with JIC fittings on each end, then I made up a bunch of adapters to 1in, anywhere from 2in to 1in and from 1/4in to 1in so I could use the valve on any system.

Install the valve in the extend hose, leave it open, extend the cylinder, then shut the valve. If the cylinder moves, you have internal leakage. If not, the problem is elsewhere.

If both cylinders have check valves, both would have to have failed to allow the boom to drift. It is definitly possible for both to have failed however.