ford 655 d

[jughead]

this thing has had a bouncy boom for a few years. i thought the bottom pins or bushings were worn. watching it today and if one drops the boom and catches it with the levers the boom cylinder rod is what is moving in and out of the cylinder about 1/2 in. fluid doesnt compress. any ideas out there today.

 

[El Hombre]

Air in the oil? Like you said, the oil doesn't compress, so that kind of leaves air in the system...

 

[jughead]

i have "operated" 5 different hoes and a couple of trackhoes and never run into this. any suggestions on how to remove air if it is. the system is full of oil.

 

[shopteacher 1]

I agree with El Hombe - it sounds like air in the line - Just like air in a brake line will make your brakes spongy. Also, I wonder if the rings on the piston in the cylinder hare bad and fluid is getting on the other side of the piston?

John

 

[jughead]

it was my understanding that there is fluid on both sides of the piston at all times just greater pressure according to which way it is going. if it is air looks like it would have bled its self out by now. my big concern is could it be the nut on the end of the shaft backing off? not trying to argue looking for any and all suggestions. i have been an auto tech for over 40 years and in that time span this old man has seen some weird stuff happen.

 

[koldsteele]

Jug I think you got it right ...Boom cylinder piston is loose .

 

[jughead]

thanks guys for the suggestions. loose nut seems probable. have only put about 450 hours on it in 5 years guess i will watch it closely and go from there

 

[El Hombre]

it was my understanding that there is fluid on both sides of the piston at all times just greater pressure according to which way it is going. if it is air looks like it would have bled its self out by now. my big concern is could it be the nut on the end of the shaft backing off? not trying to argue looking for any and all suggestions. i have been an auto tech for over 40 years and in that time span this old man has seen some weird stuff happen.

I've never seen the inside of a hydraulic cylinder, is it the end of the shaft in the piston or is it the shaft threading into the clevis? The end that's coming loose? I'm having a hard time visualizing how the shaft unthreading would cause a bounce, the thread is still engaged, if it wasn't, he couldn't move the boom up and down.

I've never had air in my hydraulics, but from what I've seen here, it tends to flush out if you work the controls enough. Kind of like cranking the steering wheel lock to lock to bleed a power steering pump or gear.

 

[jughead]

i think the piston slides on the shaft in the cylinder and is held on with a big nut. if the nut works loose then the piston can move on the shaft which MAYBE could cause the bouncing boom. never had one apart myself.

 

[DGODGR]

Jughead, you are correct. The piston is attatched to the end of the rod (the chromed part that slides in and out of the cylinder). If the nut starts to back off it can allow unwanted movement and can damage the threads if left to continue. This may or may not be the issue but you are correct in your thinking regarding cylinder design.