g741.org

Captnsim wrote:No, it would not be hard on the truck.
It's not a matter of out pulling...

so, would you sign up to feed roughly 6 tons of tensile stress through the frame of your truck?

Winch can pull 8K before the shear pin pops. Assuming the truck is VERY stuck, the winch and frictional drag are pulling on one end, and the doubler reduction pulleys are pulling on the other. Since you're feeding in 8K lbs on the winch side, it's doubled on the pulley side. That force is offset to the point it takes to overcome opposing forces.

Now, this is making the assumption that the truck is stuck to the point the shear pin would pop... if it's not stuck that bad, then the forces will be lower.

Most steel has a 36KSI yield point, that's pretty standard. The frame is 3/16" steel, times 6" high, 2" deep, plus the corner radii. You have roughly 2" of cross sectional area.

Based on that, you should be able to feed almost 72KSI through the frame before you reach the plastic deformation yield point....

BUT:

You won't catch me signing up to try this...

This works because the mechanical speed will be faster BEHIND the vehicle...Beyond that I'm not sure I can explain how it works so you can understand. Sorry

To better understand the forces involve try first not to assume that an 8,000 Lb winch is always applying an 8,000 LB pull to the cable. The 8,000LB figure is it's rated capacity not the load constantly applied to the cable. The actual cable load is a sum of the friction and rolling weight of the vehicle. Do not just jump in with 5,000 LB weight of vehicle as the applied load. The applied load is the rolling resistance of the vehicle which depends on several variables such as vehicle weight and depth of tires in muck and so on. Winch horizontal pull loads seldom approach 1/2 of winch capacity.

The pulley doubling is used to increase the mechanical advantage of one direction of movement over another. The side with the advantage will normally be the direction the vehicle will move.

http://www.4x4trailfinders.com/index.php?topic=277.0

Link with pic's...

cuz wrote:To better understand the forces involve try first not to assume that an 8,000 Lb winch is always applying an 8,000 LB pull to the cable. The 8,000LB figure is it's rated capacity not the load constantly applied to the cable. The actual cable load is a sum of the friction and rolling weight of the vehicle. Do not just jump in with 5,000 LB weight of vehicle as the applied load. The applied load is the rolling resistance of the vehicle which depends on several variables such as vehicle weight and depth of tires in muck and so on. Winch horizontal pull loads seldom approach 1/2 of winch capacity.

The pulley doubling is used to increase the mechanical advantage of one direction of movement over another. The side with the advantage will normally be the direction the vehicle will move.

correct. In my above post, I said max of 8K. Will obviously be less if the truck is not that stuck.

Yes but you still pressed your example with the 8K figure. As I said above winches seldom reach 1/2 of their capacity on horizontal rolling load pulls which are what we are discussing here. This procedure has been used thousands of times without pulling a vehicle apart.

The real safety issue with this type pull is not the truck being torn in two. It is with many cable runs which each pose a snapped flailing cable danger and if you took notice none of the runs were protected in any of the illustrations with a rug or coat draped across the cable.

Pully on the back of your model, maybe thats why she didn't work for you.

Who cares if it works or not. Lets be honest, If you were using the braden winch to do that you would die of old age. With as slow as my winch is if I had to wait for '180 of line to spool up on it I midas well walk and get help.