M936A1 Wrecker Crane Hook Not Lowering

[nf6x]

Yesterday I fired up the crane on my new M936A1 wrecker, and I found an issue that I never encountered on my old M543A2. With no load on the hook, when I push the hoist control forward the spool rotates and cable reels out from it, but the hook doesn't lower by itself. The cable just slackens underneath the boom, and I need to apply some additional tension to the cable to get the hook to lower. Additional weight on the hook works, and I can also lower it by simply grabbing the cable on top of the boom and pulling it forward while operating the hoist control. The cable is rigged as a 3-part line, just like it is on my M543A2.

The sheaves all appear to move ok, so I don't think that any of them are binding up. I'm guessing that the cable may be just stiff enough that it needs some extra tension to make it bend around the sheaves. Maybe it needs lubrication, or maybe it needs replacement? It's just barely refusing to roll around the rear sheave at the back of the boom since I can get the cable to move by pulling on it with one hand while operating the control the the other.

Have any of y'all seen this sort of thing before?

 

[73m819]

check and make sure the hook sheave along with ALL THE sheaves are turning EASY

 

[Csm Davis]

Your cable is rusty isn't it? Seen it lots of times almost always a bad cable, one reason I want a synthetic cable.

 

[nf6x]

Yes, it is rusty. I'll check all of the sheaves, but maybe my cable is just too stiff?

 

[Recovry4x4]

Drop the hoist block on the ground to remove the weight and then hand spin the sheaves. If greased properly they will turn with your fingertips. If they need grease, zap them with some quality shi...stuff. I'm hooked on synthetic grease. If that fails you, get some cable lube and lube up the cable there at the end of the boom liberally. Add some weight to the hoist block and cycle it up and down a few dozen times or more. Fresh not detergent motor oil will do in a pinch on the cable.

 

[nf6x]

My lube order says I need some VV-L-751 lubricant to lubricate my cables, but it doesn't provide a link to a web page where I can buy it. McMaster-Carr carries molybdenum disulphide based "open gear, wire rope, and cable lubricant" in 12 oz aerosol cans for around $10 each. I wonder if that would be suitable, whether it would do any good on cables that have already become rusty, and how far one can goes? There's a lot of cable on a wrecker.

If worse comes to worst, then I figured out from the TMs that I'd need just under 100' of 1/2" 6x19 fiber core wire rope to replace the hoist cable, and that would cost me around $235 at McMaster-Carr. That's not too bad.

 

[doghead]

McMaster Carr only lists 100' as the max length avail. you need 150'.

Be sure to use the right stuff!

 

[nf6x]

McMaster Carr only lists 100' as the max length avail. you need 150'.

Hmm, the -10 TM said there's 95' of crane hoist cable. Is that incorrect? Clearly I should measure what I already have before buying a replacement cable. Hopefully I won't need to replace it just yet. I'll find out after further inspection and PMCS.

I looked up the part number of the cable that the -24P said to make the hoist cable out of, and Mr. Google indicated that it's 1/2" 6x19 fiber core cable meeting fed spec RR-W-410. So the stuff at McMaster-Carr should be the right stuff, but they may or may not sell it in long enough pieces.

 

[doghead]

I thought we just had a thread on crane cable lengths. I thought we determined they had 150'. I could be wrong.

Be sure to match the max load limit of your old cable..

 

[Recovry4x4]

FWIW, I went to the local wrecker supply house that has crane and rigging supplys. Purchased 100' of 1/2 stuff that they use currently on commercial wreckers. Had a thimble swaged in one end too. Has worked flawlessly since install. The swaged thinmble is not period correct but is OSHA approved. best of all is was only 2 bucks a foot.

 

[nf6x]

The existing thimble should be reusable if it is still in good condition, right? I haven't taken one apart before, but my recollection from what I've read is that it is attached by slipping the clamping nut over the cable end, pushing a metal wedge into the cable core, and then fastening the thimble body. I got the impression that all of the components should be reusable, unlike compression tube fittings which need a new ferrule.

I was testing out the front winch yesterday and really wishing that I had either a helper or a way to actuate the winch motor from outside the truck. Operating the winch from the driver seat doesn't seem like a problem, but getting that last few feet of cable stowed was a pain: get out of the cab to see how much is left, climb back in and guess how long to pull the lever, then climb out and repeat. There was also some more climbing in and out to blip the control to allow the winch clutch to be engaged and disengaged. If there is a convenient place to mount a small double acting air cylinder somewhere to actuate the control lever, then I don't think it would be too hard to add the cylinder, a solenoid operated air valve, and a plug for a wired winch remote control like one of the surplus HMMWV ones that are all over eBay right now. The winch moves slowly enough at engine idle that I don't think that proportional control is needed. Even a switch mounted at the front of the truck would be helpful, and that could be a manual directional air valve in place of a solenoid operated valve. I might try something like this since I usually don't have a soldier B handy. I think the electric remote approach should cost around $300 using new parts from McMaster Carr, a remote control from eBay, and some other odds and ends.

The cable tensioner and level wind did exactly what they're supposed to. Yay!

A remote might be handy on the rear winch, too, since it can't free wheel to let a single operator pull the cable out. If any of y'all have managed to make effective use of the rear winch without a helper, I'd like to hear how you did it. I gave up trying on my M543A2, but it has the added complication of the controls not being reachable from ground level.

 

[doghead]

Fwiw, here's the thread I was thinking about. I found it searching for "crane cable".

http://www.steelsoldiers.com/deuce/91074-need-length-cable-wire-rope-m108-crane.html

 

[FormerNewMVGuy]

Drop the hoist block on the ground to remove the weight and then hand spin the sheaves. If greased properly they will turn with your fingertips. If they need grease, zap them with some quality shi...stuff. I'm hooked on synthetic grease. If that fails you, get some cable lube and lube up the cable there at the end of the boom liberally. Add some weight to the hoist block and cycle it up and down a few dozen times or more. Fresh not detergent motor oil will do in a pinch on the cable.

I've been using 30wt Nondetergent motor oil on my winch cables, on deuce and 5 ton.
I recently had all the cable payed out on the deuce, and the cable was in beautiful condition, I know the regular cable lube is prolly better , but i'm really happy with the results of the nondetergent motor oil.

 

[nf6x]

Fwiw, here's the thread I was thinking about. I found it searching for "crane cable".

http://www.steelsoldiers.com/deuce/91074-need-length-cable-wire-rope-m108-crane.html

I think that the crane is different on the M108. If my memory serves me right, doesn't it have a longer boom with both hydraulic and manual extensions? Comments from folks about replacing the cables on M543A2 (very similar crane to the M936, as far as I can tell) suggest that the 95' number from the -10 TM is probably correct. In any case, I'll measure what I have before trying to replace it. It fills the spool with the block all the way up, so it should presently have the right cable length.