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Wrecker wishlist of mods

73m819

73m819

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The reason for the weight kit is that the standard wrecker has the crane almost over the trunion and the drag winch behind the trunion, this coupled to a heavy lift tow over the rear tends to lift the front end causing the front tires to go lite and loss of steering (pushing the front tires in a turn). The standard older military wreckers ALWAYS had this problem, the a2s with the lighter motor has even more of a proplem.
 
Csm Davis

Csm Davis

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73m819 said:
The reason for the weight kit is that the standard wrecker has the crane almost over the trunion and the drag winch behind the trunion, this coupled to a heavy lift tow over the rear tends to lift the front end causing the front tires to go lite and loss of steering (pushing the front tires in a turn). The standard older military wreckers ALWAYS had this problem, the a2s with the lighter motor has even more of a proplem.
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Yeah bud I think everyone is up with that you need to add weight on the front of the wrecker. That's why we are confused by your other post.
 
mdmorgan

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I was lift towing a 5 ton expando van and when I got to the bottom of the on ramp to the highway there was a slight dip that felt more like a ramp! The front tires of the wrecker came off the ground by at least a foot and floated up there for about 15-20 feet before touching back down. It was kinda fun and really scary at the same time. I pulled over, let the truck down and flat towed it the rest of the way home. Wish I would have got it on video.
 
mdmorgan

mdmorgan

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zebedee said:
splendid attempt there Jeff. Chalenge accepted.

mdmorgan - shame you didn't get pic!
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Yeah, well I wasn't expecting it to happen, and I was probably doing 40-45mph when it happened. What's weird is it was so smooth that if I hadn't been looking at the sky or lost directional control I wouldn't know it even happened. Next time I pick up a truck I'll send a camera ahead to get it:beer:
 
Csm Davis

Csm Davis

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That add on kit is what got me to thinking about front toolboxes. Why add extra weight that's not needed, just put boxes there to hold the heavy junk you already have. And as a side bonus you will stiffen you bumper and frame up front which is the only place I have seen the 5 tons bend, even in a crash.
 
R

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If I recall correctly, when the A2 family was introduced the wrecker front weight "add on" just about made up the difference in weight between the 855 and the 8.3 engines (just a few hundred pounds..maybe 500?). FWIW, it is hard to judge the weight of steel in block form (plate, bar, etc)...people usually guess too high for whatever reason.
My neighbor works at a manufacturing company where they fabricate large forestry machines, they always plug in material type and dimensions into an app on a smart phone before craning large sections of steel to be sure that the electro magnet being used is is strong enough. He is the one who told me that they tend to guess on the heavy side (and these guys build machines weighing more than 60 tons!).
Regards, Bob
 
73m819

73m819

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VERY easy to figure the weight of steel, a 1" x 12" x12" piece of steel weighs very close to 41 lbs,, from knowing this and some basic math, about any size or shape can be figured out to a very close total weight. REMEMBER it is better to be a bit on the heavy side then on the lite side.
 
zebedee

zebedee

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OK. Agreeing that the front of 543/816/936 is a little on the light side and would benefit from more lbs - be it useless plates or ground anchors/pins (Scammell/AEC/Martian etc.) or Bii lockers behind the bumper... Maybe we could look at the simple mathematic equation from the other standpoint, namely the rear pivot..

As Ron has said, the 819 "tractor wreckers" perform better as a suspend tow vehicle, due to the greater distance of the rear lift point relative to the CG of the overall mass of the truck; how about introducing a couple of air springs somewhere on the rear axle, inflated at the flip of a switch only when sus'towing.

I had a look under my 816 and think that at the expence of a little off road axle travel, a pair of air bags could stiffen up the rear bogie, hence moving the pivot point back from the center of the bogie, to the center of the rear most axle.
As discusses eariler/elsewhere, axle lock outs would help for side lifting instead of deployment of the stabilisers, in the same way, stopping the bogie from pivoting, would significantly effect the nose weight... think 100's of ft/lbs since we are talking torque or rotational effort... like a see-saw;
airbags rear axle calcs.jpg
value in "tons" under front axle of equivalent reaction to load on rear, so almost 1 ton less needed to keep front wheels on ground not taking into account inherant vehicle weight.

Before anyone shouts out "overloading of rear tires" think about the truck with no suspension. The deformation of the rear tires would occur at a tangent to the front axle, many feet infront, so for a compression of 1/2" of the second axle, the rear axle would only compress 1/2" plus a small fraction more.
Since we are not changing the capacity of the truck, simply shutting down the ability of the suspension to follow uneaven ground - this could be a weight saving and valuable mod for porely designed (or compromised capabilities of multi purpose..) wreckers.
 
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jesusgatos

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Would be surprised if all those plates add up to much more than 500lbs. Isn't the front axle rating going to become an issue pretty quickly? Remember reading a white paper someone published about adapting these M939 trucks to serve as wildfire trucks and if I remember correctly the front axle wasn't up to the task. All the numbers were published, but I don't remember them off-hand.
 
Welder Sam

Welder Sam

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jesusgatos said:
Would be surprised if all those plates add up to much more than 500lbs. Isn't the front axle rating going to become an issue pretty quickly? Remember reading a white paper someone published about adapting these M939 trucks to serve as wildfire trucks and if I remember correctly the front axle wasn't up to the task. All the numbers were published, but I don't remember them off-hand.
Click to expand...
If 939 trucks arent up to the task, neither are/were 809 and 39 trucks right? All the same axle?
 
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