[2500 Grunt]

Do Chrysler engineers use a formula or a value or rating for determining the shear or tensile stress on our rear axle or 5th wheel hitch? I know that there isn't a practical way of users to determine what it is but...Everything that is talked about with specs is just load or vertical load? If I have a 17000# toy hauler fully loaded and have a 1400# plus sandrail behind the 3 axles then my pin weight might be within the 6000# GAWR of the truck (6000#- rear axle truck dry scale weight) because of the location of the sandrail load but what about the pull or tow weight of the load/toy hauler? Or do you assume that my 6000#GAWR vertical load of the truck is the weak factor. In other words, can the internals of the rear axle or be over worked with a horizontal load before you hit the GAWR of 6000#. My father in law fried a bearing in his rear axle pulling a heavy toy hauler recently. Yes, he was over loaded and never had it on the scales but I am curious why horizontal load is never discussed or is it worked into the vertical load specs? Or am I just missing something??

 

[carlsonr]

only 2 patings ive ever read references on. payload which is any load on or in the bed and cab of truck, usually about 3000 pounds.then the gross combined vehicle weight (GCVW) which is the total combined weight of every thing in the truck and being pulled by the truck,usually about 16000 pounds.most people routinely excede these, so stuff will break.

 

[carl48]

do not worry about it. us heavy haulers have to register our trucks a different way. the 26,000 lbs cgw is a maximum for private trucks. and has nothing to do with strength. under business trucks you register it for the total cgw of the heaviest load. the truck in the pix is registered for 45,000 lbs it is set up at 425 hp and 850 ft lbs torque. some of our trucks have near or over 1,000,000 miles on them. no broken axles, transmissions or engine failures on any of them. the pix is a line truck i brought back from north Carolina a 3,200 mile round trip. i grossed 32,400 up and with the truck 39,600

 

[2500 Grunt]

I know there are a lot of heavy haulers because I see them all of the time here in AZ but I'm still curious about the pull strength though? I'm pretty sure that you can stay under the 3000# pin weight with load adjustment on the hauler but the extra weight is still there for the truck to pull putting that extra horizontal load on the axle components? I'm trying to find out where to get some spec's on my rear 11.5 AAM.

 

[STONR]

I don't know of any horizontal load specs. I would start measuring differential temperature. The more load/power you apply to the axle, the hotter it will get. You could pull a super heavy load at a slow speed (like the Toyota pulling the space shuttle), or a lighter load at a higher speed (real world tow weights) and end up with the same differential temperature.

With the amount of power that our trucks have (and are capable of making), followed up by a heavy trailer (not just pin/hitch weight but gross trailer weight), factor in wind resistance and hills/gravity... You could cook the gear lube. This is why the new 800ft-lb Max Tow Dodge came with a different differential cover with cooling fins.

The weakest link is the u joints, or loss of traction.
The weakest link long-term I think is heat.

 

[lpennock]

I don't know of any horizontal load specs.

There is one but I've never seen it published any where. At some point the twisting forces on the axle or pinion or the shear forces on the ring and pinion teeth will become enough to break something. I would guess it is somewhere around 3000ft-lb as according to Dana the Dana80 is good for input torque of 3000 Ft-LB <http://www.crateaxle.com/products/dana-80-axles> and the AAM 11.5 is in the same class.

I would agree with you that heat is the biggest concern though. I would expect tire traction to give up before the torque limit was reached; however, a good shock load like a tire spinning in the air and slamming into the ground while towing a heavy load might exceed the maximum torque.

 

[ykdave]

like mentioned, their is no such rating, unless you were looking to hang the tailer off a cliff and held up by the axle (in which case its load rating would come into effect!)

Just because you have a 20,000lb trailer, doesnt mean the "horizontal load" is 20,000lbs. their is no such measurement as this cannot be accurately measured and would vary greatly depending on conditions

The load rating of the axle (vertical) is the rated load that the spindles/wheel bearings and housing can support. this could of course also be used as your "horizontal" load as the stresses on the components are similar.

The tow rating used by dodge (GCVWR) is more of a reflection on the trucks construction than the axle itself. You have to take into consideration the stresses transferred through the driveline, the springs, frame and ultimately the hitch system. Dodge of course always sways on the light side of things to reduce wear and tear as well as saving their azz when someone crashes pulling a huge load.

You could call AAM, as with Dana, they can tell you the axle's (and the axle only) design limits. they should be able to tell you the load rating as well as input torque and an estimated max GCVWR. Of course this in no way means that if they say that axle is good for 50k gcvw, that you wont tear the rest of the truck to pieces LOL

Like mentioned, input torque and heat are the biggest things to watch. you could pull a 5 billion pound trailer with it, if the load on the axle didnt exceed its rating and you didnt exceed its torque rating (granted the torque was enough to move the trailer!)