580B Boom Falling Fast

[Anonymous-0]

I have a 580B and the backhoe boom falls very quickly. There is no external leak so it has to be either the packings or the spool leaking internally. Is there any way to tell which is leaking? I don't want to spend the time and money repairing something if it isn't broken. Thanks

 

[wayne2]

Ain't that expensive-maybe 2 hrs. OK 6-8 if parts arn't around-day trip when was the last time???????? wayne

 

[Roger (Mi)]

A valve spool will NOT leak in the manner that you've described. Replace the packings in both of the boom lift cylinders.

 

[mEl]

Get a JIC cap and cap the rod end of the boom cylinder and pick the dipper up to put weight on the boom cyl. If it still leaks down replace packing. If it does not, find the secondary relief valve next to the spool for that circuit, remove it and check for bad or missing O ring or a failed valve, a authorize dealer should have a test fixture to screw the valve into to check it for proper pressure and leakage( seat damage) Also the check valve plug underneath the secondary valve should be removed and checked for missing o rings also. The Case service manual shows how to make a simple tool out of a 3/8 bolt to remove it easily. Good luck, mEl

 

[mEl]

Forgot!! check for damage to the boom cylinder barrels in the area where they would contact the stabilizer pads if swung to the extermes with the pads up. if the barrels are dinged the packings are most likely destroyed and barrels and pistons will have to be replaced (a common operator error problem). Warm the oil in the system, hold pressure in the boom up for a extended period of time and feel where the pistons shoud be in the cylinder. Hot spots on the exterior of the barrel will pinpoint the leak. mEl

 

[Roger (Mi)]

The secondary reliefs on the boom valve spool are ONLY active when raising the boom or using downward pressure with the boom. Once the valve spool is in the middle (neutral) position, the secondary reliefs play no part in keeping the boom up. An excellent point about damaged cylinders. No amount of packing will help in that situation.

 

[mEl]

Rodger, The purpose of a secondary is to protect the cylinder from hydraulic loads produced by mechanical forces either pushing or pulling the rod by mechanical force produced by rolling the bucket or pulling the dipper,etc, as such, it must be of necessity located between the spool and the cylinder. I have been working on these units since starting to work at the Case dealership where I presently work since 1962, have been factory trained on all units up to and including the M series hoes. I have set many secondaries up above factory spec to improve a hoe's craning ability for setting manholes, etc. The fact that that can be done proves that the secondary is between the cyl and the spool, as boom squash out occours with a closed spool, damaged o rings on a secondary cartridge or a damaged or worn secondary valve seat WILL cause boom leakdown. mEl

 

[Roger (Mi)]

mEl,

I too worked at Case dealerships as a mechanic. I've been to numberous schools at Racine as well.

Additionally, I own a 580B loader/backhoe. It's one great machine given its small size. The following is from my own experience. I was trying to lift and set a large septic into a hole. When I pulled back on the boom lift lever, it would not lift the tank. The boom secondary relief was opening. I then curled the dipper, raised the boom, then straightened the dipper. Up it went! Why didn't the boom secondary relief open again and everything settle to the ground? My service manual does not show a hydraulic flow diagram. Now, I'm curious. I checked the Internet for Cross and Cessna control valves for Case backhoes but with no luck. I'll need to go my local industrial dealer and ask to see their book.

 

[Anonymous-0]

Thanks for the info. I will try the caps on the cylinders to isolate the packing as the casue and go from there. Thanks again.

 

[mEl]

The answer to your question is as follows, the lifting ability of the boom cylinder is controlled by main relief, but the secondary is set to pop at a much higher pressure, hence the boom cylinder will hold a weight it cannot pick. But as you experienced , the boom did hold while craning with the dipper( the much stronger circuit to crane with). One must differentiate between the main relief, located in the loader contol valve and the secondary relief located next to the spool for the circuit involved , also not all circuits on the hoe have secondaries. Mel

 

[Anonymous-0]

It was the packings.