Whose Fault? - Dodge or Hitch Builders?


The most important knowledge you can have is knowing what you do not know.  So when I started collecting and restoring trucks, I went to the local community college and earned an Associate Degree in Body Shop Management and Auto Body Repair.  This discussion combines classroom education and observing the real world. 


Among the classes in the curriculum was front end alignment.  There are no figures in the alignment specification manuals for aligning a front end with less weight on the axle when being driven than when parked.  Let’s apply this classroom training and observe trucks that pull real loads.  Pulling a Jet Ski on a trailer is not a real load.


A farmer knows better than to pull with the load connected above the rear tractor axle.  The same goes for hitching the sled at truck and tractor pulls.   Many of the Dodge front end problems occurred when pulling trailers with a gooseneck or fifth wheel hitch.  These trailers were also carrying loads generally above those specified by the manufacturer.  I know my loads were.  These hitches apply the pulling force above the rear axle centerline.  In my high school physics classroom, I learned about vectors.


You can diagram the vector forces affecting a hitch.  It would take sophisticated measuring devices to determine the quantities of the vector diagram so let’s do this with estimates.


The first force is the hitch weight.  This is constant whether the truck and trailer rig is moving or standing still.  Draw this as a line straight down from the point where the trailer ball or pin is connected to the hitch.


The second force is the startup load.  When starting to move, the whole weight of the loaded trailer is applied to the ball or pin as a rearward force.  This is when the greatest amount of pull occurs.  Observe a heavily loaded semi-tractor when starting to move.  Not only does the front of the tractor rise, it also reacts to the twisting force applied by drive shaft torque to the rear axles and one side of the tractor front rises more than the other.  This force occurs infrequently and only briefly and does not affect the front end alignment for purposes of this discussion.  It does affect the design and installation of the hitch set up and should always be considered.


The third force or rolling load diminishes once the rig gets up to speed.  Then, instead of the total weight of the trailer and cargo, the rolling load consists more of rolling resistance – drag from air resistance, and from tire and wheel bearing friction.  Since most driving occurs when this force is affecting the alignment, this is the one that applies to this discussion and should be considered when preparing the hitch force vector diagram.  Without load sensors in the hitch assembly, you can only estimate the amount of this force.  Draw this force as a line straight back from the ball or pin. 


Now you have a vertical line (hitch weight) at the front of your diagram and a horizontal line (rolling resistance) at the top.  These lines form a 90 degree angle at the hitch ball or pin.  Draw these lines to scale so their lengths represent the units of force measurement.  Now, complete the rectangle with a horizontal line rearward from the bottom of the vertical line that comes down from the hitch ball or pin.  Close the rectangle with a vertical line connecting the trailer ends of the two horizontal lines.


Draw a line from the hitch corner of the diagram diagonally to the corner at the lower, trailer end of the diagram.  That line represents the vector, or path of the force applied to the hitch. 


If that line goes through or below the point on the truck where power is applied to the ground, the lift we see on the big rig will not occur and the pulling truck’s front axle is under the same or greater weight as when parked.  This is a condition where the alignment specifications cover the situation. 


If that line goes above the point on the truck where the power is applied to the ground, the lift we see on the big rig will occur anytime the pulling truck is moving and the weight on the front axle will be negative or less than when parked.  This effectively puts the alignment specifications on the wrong side of where they should be. 


Now, the engineers can spend time arguing about some of the terms I’ve used.  It’s not an EGO thing with me.  I’m not writing this for engineers.  Some know it.  Others design poorly engineered hitch set ups. 


One valid point of technical argument is identifying the point in the diagram where the power is applied to the ground.  One faction says it is where the tire makes contact with the ground.  Another faction will say it at the axle centerline.  I tend to go with the tire contact point, but my own experience makes me satisfied to have my vector diagram work when using the axle centerline. 


The point is that when you have a gooseneck ball mounted an inch or two in front of the rear axle, you will move to a “negative” front alignment situation.  Raise the fifth wheel hitch a foot higher and you have made it even worse. 


I had a gooseneck trailer with a 36 foot flatbed.  At the end of a haul to Texas from Fairfield with two trucks and some other parts, I took it onto a scale.  The combined gross vehicle weight was 26,040 pounds – over the limit and without the driver (add 215#)  I weighed the front axle and found it weighed 300 pounds more than it did with no trailer.  There’s no way that 300 pounds did not go away and then some when I was pulling. 




When I was unable to find a hitch installation that departed from the “bubba” rural welding shop tradition, I built my own gooseneck ball hitch.  It was adjustable to four positions, the forward most being 12” ahead of the rear axle.  The hitch ball plate mounting holes were asymmetrical so that when the plate was rotated an refastened to the same mounting bolts, the ball moved 4 inches.  There were two more ball positions with the hitch ball plate on the rear two sets of mounting bolts.  The receiver hitch was for my trailer loading winch with a receiver hitch mount. 



In a later two-truck haul, I hit a “CAT” scale at a truck stop and found that I had moved 1000 pounds to the front axle – well within the GAWR.  The truck rode well and my tires lasted past trade-in.


My first four Dodge CTD trucks were all 2WD.  I believe 2WD front alignments are a bit more tolerant than the 4WD.  As I recall some of the online discussions, the 4WD seemed to have a majority of the front end problems. 

Clearly, improperly mounted hitches with overloaded trailers were as much – or more – to blame than Dodge engineering.  I believe Dodge has engineered more alignment tolerance into successive years of trucks since this problem seems to have diminished.