Question about CMP winch?

[Phil Waterman]

What pull are they rated at?

I’ve looked through my various manuals and though I think I remember seeing it once I can’t seem to find it. My reason for asking is that I finally mounted the 125 feet of 5/8 in cable on my 1941 C60L and well if you’ve got a winch why not use it. But looking at the breaking strength of the cable 20.6 Tons I realized that this is not something you want to use with 3/8 chain from the hardware store.

One of the first things I discovered/read in the drivers handbook is that the cable must be wound on to the drum under tension. In doing this I soon discovered that the winch was perfectly happy to drag the truck with the brakes locked on. After a couple of tries I learned the proper amount of brake to wind cable on smoothly. Then I started playing a little with the winch, thanks to Bob I have a pair of the winch scotches my first experiment was to place the scotches as shown in the book using some 6000 lb tow cable and chain lengths for proper adjustment. With the truck sitting on the hard packed gravel drive and the cable run out 50 feet and chained to a very large pine tree, transfer case in winch position, slowly released the clutch and the cable brake and throttle just above idle, the truck started to move slowly back as the scotches sank into the ground and the truck just kept moving. The scotches just cutting two trenches, then I applied the brakes both drum and parking to check what was happening under tension.

What was very clear is that there is a great deal of pulling power available, two that the light chains and cable I’d used on the scotches were exceeding their useable strength (near breaking), third that if I’m going to actually use the winch I should use only scotch cables and attachment chains that are rated to the capacity of the winch. Hence my question what is the rated capacity of the winch?

One last point unlike most US Military winches that have a shear pin which is defeated when it breaks the first time and is replaced with a harden bolt, I don’t remember seeing any designed shear pin in the CMP winch, is there one?

[Grant Bowker]

There is no provision for a shear pin as such on the setup used in the 101" wheelbase. The front of the flexible coupling is keyed to the output shaft of the transfer case and the rear of the coupling has 4 bolts similar to a universal joint (probably the same bolt pattern on the input of all versions of the winch but this hasn't been checked in the parts manuals). From memory, I think the cross section of the bolts exceeds the key but the areas are close enough that it would depend on the materials of the two parts which failed first. Neither one counts as a user freindly, field replacement item like a real shear pin should be.

[hrpearce]

Hi Phil,
I don't know the rated pull of the winch but when I got my blitz it was set up for log snigging. It's got a heavy 4" box section welded across the back of the chassis to back it up to a tree to ancre it. My Father in law said that if you used scotches and a log snaged the U bolts holding the axle on snaped.
The winch on mine was mounted above the chassis and geared down 2 to 1and even having double the engine power going to the winch the engine stalled before you reached the capasity of bolts or keys.

[Bob Carriere]

Hi Phil

Can't put my finger on it but I have references to 14000 pounds for the winch.

Now if the set up on my truck is correct the gear selection affects the speed an power of the winch..... in other words 4 speed forward when retrieving and one reverse when powering the rope off the drum.

I suspect that with the engine in high 4th gear at idle.... you would stall the 82 HP engine before shearing anything.

My expereince with winches is limited tot he Dodge M37 which conveniently blew a shear pin everytime the sucker was buried in deep mud..... installing a new pin meant digging a hole.... that filled with water/mud....... an laying on your back to replace the pin. Being ingenious and stupid we replaced our soft pins made of cheap 4 inch nails with concrete nails..... voila!!!!

When skidding heavy large dead elms the weigth of the tree trunk would pull the Dodge forward even with all four wheels locked.... so I would let it roll until I could rest the front bumper on a suitable stump..... push the gas..... and the screw drive held by 4 bolts on the face of the winch where the drive shaft would go in...... actually sheared and pulled itself out of the winch bending the small drive haft...... a visit to the junk yard for the parts set me back $350 for part of the truck I had purchased for $700...... was more carefull after that.

I am sure that nay heavy winching would have included tying the front of the truck's D rings onto something of substance. You are correct in making sure the end chain, hook, ect. is on par to the full potential of the winch.

When working with the Dodge we very seldomed used any engine speed above idle and still managed to pull other civilian 4x4 Blazers, etc. without any hesitation.

I would suggest getting/using a surplus deuce winch chains set for the CMP as they are probably readily available in the states.

How much cable could you safely wind up on the winch drum...?

Bob

[Keith Orpin]

Guys,
I've just been though my reference books and various manuals, and the plot thickens !
If you reference the early manuals, (and to be honest there is very little mentioned) they suggest 125ft of 5/8" cable should be used. However, if you refer to the MBC2 manual, it states that 125ft of 11/16" cable should be used, giving a figure of 14500 lbs as the winch capacity, little wonder Phil that your C60 was being dragged backwards !
Like Bob, I thought I had seen reference to 14000 lbs somewhere else, but so far this is the only evidence I have found.
As for a shear pin, I can find no mention of one, in any of the parts books or manuals, nor do I remember finding one when I rebuilt my Chevy.
Keep looking guys
Regards
Keith

[Phil Waterman]

Hi Keith and Everybody

You are correct in that the manual calls for 11/16th cable but as that is not readily available, I went with 5/8ths whats a 1/16th among friends.

Where did you find the figure of 14,500 lbs this is what I have not been able to find.

My reasons for asking these questions is that I know how much energy can be stored in a steel cable. Does anybody have a strength figure for 1941 11/16th cable as compared to modern cable?

Not with the winch but in the past I have seen what happens when you start loading steel cables near to breaking. I've shared the picture below the result of trying to pull a 4,000lb truck out of a snow bank with a 11,000 lb CMP the with a tow cable rated at 6000 lbs math just doesn't work, but the cable didn't break.

I'm really trying to figure out how to load limit the winch and attachments to something less than breaking strength.

The Ice Storm of 2009 has left me with a lot of broken and dieing trees that I want to snake out with out cutting truck sized holes around the house. Also I don't want to end up wearing a chunk of cable, or chain.

From the load in the truck you can see what I'm up to.

[Bob Carriere]

I know you like playing with the big truck like a big boy...... but it would be safer and simpler to buy a 8000 pound modern electric winch ...... cable is much lighter to use.....use a snatch block to double the pulling power or do angle pulling...... beauty is it will stall if over loaded... long before a good cable will break.

will look again for reference to winch capacity.

Boob

[Lynn Eades]

Surely you must be able to purchase something you can inlude in your rig, an element, with a known failure rate, or measues the load. Something in your rope behind the hook, that gives you a load measurement, regardless of how many layers of rope are on the drum.

[Keith Webb]

On Australian CMPs fitted with the standard chassis mounted winch there was a brass data plate added which gave the rated load as 7,000 lb not twice that. From memory the Servex winch fitted here to the C60X and some wreckers was rated higher.

The attached pic is of a winch plate on a F60L cab 12 which Ganmain Tony may recognise.

[Keith Orpin]

Hi Phil et al,
The only info I have found so far came from Maintenance manual MB-C2W, dated Sept 1943. In sub-section O, there is an 8 page section on the winch. On page O7 the spec of the winch is given, see attached picture of part of this page, showing the 14500 figure (actually, it's shown in Tons).
Hope this helps, and let me know if you require any more pictures
All the best,
Keith

[Phil Waterman]

Well that's two conflicting answers that only deepens the mystery. First thanks to everybody for trying to find a definitive answer.

Keith you found the rating that I remembered, kind of interesting that it gives it in tons. Which leaves us with long tons 2240 lbs or short ton 2000 lbs both are used in manuals CMPs sometimes with no indication of which. So that would give us a capacity of 14.5 tons which could be 32,480 lbs or 29,000 lbs a significant variance. I suspect that this breaking strength of cable and I suspect the figure on the data plate Keith found of 7500 lbs is the working load lifting load.

The wide variance in these figures is why I asked the question in the first place, because as has been pointed out the winch system is only as strong as the weakest part. Which if and when it breaks release all the energy stored in unspooled cable which can be considerable.

Bob as to the suggestion of a electric winch, where would be the challenge in that besides as you will note in the picture I've mounted a hydraulic lifting arm on the truck already 500-1000 lbs capacity with a 1750 lbs Warn electric winch. This is very useful for loading engines, steel beams etc into the truck. (much better than my back)

Half the fun (justification) for having three trucks is using them, being a little older and wisher I hope using with out breaking or wearing a bit of winch gear.

For now I think I will go with the approach of improving all my load attachment gear, ie chains, load straps, scotch cables up to atleast 12,000 lbs to match the snatch block I have. The point raised by Grant and hrpearce about load chaining the truck down. I think I'll go with letting the holding power of the scotches and engine at high idle be the load limiters.

I'll keep you posted on what I find.

But it would really be interesting to find a real answers to the design capacity of CMP winches. Or is this another case of they designed as heavy as they could and hoped it would be strong enough to do the job in the field.

On last point the long chassis with winch doesn't use the flex joint found on the 101 wheelbase units. It has all normal drive shafts though they are a little lighter design than the regular drive shafts.

Pictures of winch work to follow.

[Barry Churcher]

Phil, I don't have the correct answer to your query but I do know that if the winches are heavily loaded the frame will twist before anything breaks. When I was working on my artillery tractor I went through three badly twisted chassis before I found a good one. The best chassis came from a truck that had spent it's life as a tow truck.
Cheers,
Barry

[Grant Bowker]

Vol 4 of the AEDB Design Record lists the capacity for the chassis winch as "The maximum pull developed by this winch is 11,000 pounds with a ratio of 6.2 to 1 in the winch drive unit."
From the same source: "125 feet of 5/8" diameter cable was normally fitted on this drum."
Yet another, different answer.......

[Lynn Eades]

Back then ,I would say your winch is rated in long tons. Short tons were used for shipping purposes.
Now Tony's going to say something profound

[Tony Smith]

Or we can try to calculate it?

The Ford Engine makes 178 ft lbs of torque. Multiply by 6.4:1 1st gear gives 1139.2 ft lbs. Multiply by the winch ratio of 6.66:1 gives 7587 ft lbs. What is the diameter of the winch drum? If we hypothetically say the layer of cable is 8 inches from the centreline if the drum (divide by .66), that gives us 11495 lbs of pull.

The Chev engine will have different torque (170 ft lbs @ 1200) and gear (7.058 to 1) figures, and the actual diameter of the drum needs to be measured, but are we in the ballpark?

[Phil Waterman]

Originally Posted by Barry Churcher

Phil, I don't have the correct answer to your query but I do know that if the winches are heavily loaded the frame will twist before anything breaks. When I was working on my artillery tractor I went through three badly twisted chassis before I found a good one. The best chassis came from a truck that had spent it's life as a tow truck.
Cheers,
Barry

Barry - You hit the nail on the head about hard use, this particular 1941 C60L had been hard used and abused. It spent part of its life building Mount Ascutney Ski Area in Vermont, from the cable reel frame on the back it was used to drag cable up the mountain. It had been rolled at one point bending the cab frame and brake peddle, the clutch housing had so many cracks in that when you tapped it with a hammer it went thud.

The winch guides all showed evidence of hard use and have actually been worn by the cable pulling across them. Given all that one of the first things I did was check all the diagonal measurements across the frame and the silly thing was straight and flat.

In parts of the world where there are multiple CMPs to choose from I'm sure that this one would have been considered a parts truck.

[Phil Waterman]

Originally Posted by Barry Churcher

Phil, I don't have the correct answer to your query but I do know that if the winches are heavily loaded the frame will twist before anything breaks. When I was working on my artillery tractor I went through three badly twisted chassis before I found a good one. The best chassis came from a truck that had spent it's life as a tow truck.
Cheers,
Barry

Barry - You hit the nail on the head about hard use, this particular 1941 C60L had been hard used and abused. It spent part of its life building Mount Ascutney Ski Area in Vermont, from the cable reel frame on the back it was used to drag cable up the mountain. It had been rolled at one point bending the cab frame and brake peddle, the clutch housing had so many cracks in that when you tapped it with a hammer it went thud.

The winch guides all showed evidence of hard use and have actually been worn by the cable pulling across them. Given all that one of the first things I did was check all the diagonal measurements across the frame and the silly thing was straight and flat.

In parts of the world where there are multiple CMPs to choose from I'm sure that this one would have been considered a parts truck.