National crane proportioning cable issues

[Daniel Bluff Jr]

2000 series 1300, model 13105, believe it the "A" type.

There are two cables running above the center boom section attached to the lower portion, through a sheave and back to anchor at the bottom of the main boom. I believe they are "proportioning cables". The right cable keeps coming off the sheave at the top when the boom is fully extended and in doing so becomes damaged.

I'm hoping to find an older service manual as the current offering for the late model crane booms have only one cable rather than the two.

The sheaves have no wear, damage, or any other defects. Both anchors are secure. No other issues with the boom and the problem has been a constant one. 3 cables so far. First set installed professionally and we suspected the left and right had been crossed thus causing them to break, now I'm not sure.

 

[Daniel Bluff Jr]

So thanks to a few calls to manitowoc I was able.to get the neccessary information. However I am left with a question in regards to the "cable tension tool" mentioned in the procedure. It states it can be done without but we all know how much easier things go with the right tools.

Does anyone have information on what it is? Perhaps where I can get it. I'm assuming it's a torque wrench with extended reach. I can use a torque wrench with extensions but I understand that it may not be accurate. Given the specs are relative and a comparison between each set of cables anyway I dont think it would matter so long as whatever deviation from true is consistent between measurements.

 

[Vetech63]

Use a standard torque wrench......add 1 ft lbs per inch of extension.

 

[crane operator]

I've never seen a cable tensioning tool. I've always just put them back where they were for tension, by measuring threads protuding from the nuts. It sounds like you have one cable tighter / looser than the other, or possibly your wear pads are out of adjustment- allowiing the boom to be too crooked on extension. This is causing the offside cable to get loose and making it jump the sheave.

 

[funwithfuel]

As crane op says, one's probably looser than the other. That said, I worked for a National dealer for a short time. I will say the extend/retract sheaves have a tendency to eat through their bushings. (No one likes to grease the bearing cuz it's a PITA to line up the access hole.) This will result in inconsistent tension, especially with worn wear pads . At full extension, it's not uncommon for guys to move the swing or elevation too suddenly and dislodge the wear pads. I think you may want to perform a complete teardown and inspection. There is too much liability involved with anything suspended. It's not worth the risk.
Good luck and be safe.

 

[HATCHEQUIP]

Old thread but allso make sure all sections are bottoming out on extension and retraction at the same time and replace cables as sets , after replacing cables run the machine with test weights and then recheck cables then do it again after a few weeks or months .