The culprit will be anything that increases dynamic loading on the tongue
Texas_Camper said:
I was wondering what the parameters could be:
Lift Kit
WD Hitch
Swing Tongue
Heavier Axles
Larger Tires
Water Tanks Filled
And,,, date of mfg of the trailers involved...
Might be interesting when all the facts are in...if they ever are......
One thing that Michael Hulsey and I (as well as several others who've contributed to this thread) can definitely agree on is that the cause of these fractures is
repetitive and
large dynamic loads concentrated in a small area (i.e. the attach points of the swing tongue hinge).
That means we can immediately discard any factor that does
not effect the static or dynamic tongue loading, or in other words, factors like lift kits, heavier axles, larger tires, etc. are unlikely to have any effect.
What
does contribute is anything that increases static and especially dynamic loading on the tongue. And more importantly, any factor that concentrates all that loading on one side of the tongue...which is pretty much what the swing tongue does since there is enough slop in the hinge that a substantial amount of torque has to occur before the other side makes contact. Therefore, this is definitely only going to be an issue with swing tongue TMs. And it is likely going to be more of a factor where manufacturing variances resulted in a slightly larger gap between the two parts of the tongue when it is locked in the closed/towing position.
To clarify things, static loads are those that exist when the trailer is not moving. Dynamic loads are those that come from movement of the trailer....when it is subject to road shocks and pulling forces from the tow vehicle. Most static loads become dynamic loads...a 650 lb static tongue weight can easily become a transient 1200 lb dynamic tongue weight if the rear of the tow vehicle encounters a pothole or bump or at speed and that road imperfection causes the hitch ball to sharply/rapidly rise or drop (2G), even if the vertical movement of the hitch ball is only 1/2 inch. However, some static loads do not become dynamic loads....for instance if the swing tongue is rotated to the side with the trailer resting on it, you have a static load (of maybe 600 lbs) that will not become a dynamic load. And some dynamic loads have no static equivalent...for instance, in mountain towing on sharply curving roads there are large lateral (side to side) dynamic forces on the tongue caused simply by the tow vehicle forcing the trailer to suddenly change directions during cornering.
Focusing on static loads....these will include front loaded weight within the trailer (e.g. full water tanks on the models that have the tanks under a front couch); stowing of heavy items in the front of the trailer; and most importantly the use of a WDH. For instance, the use of a WDH with 750# spring bars with those bars at 80% deflection when the trailer is not moving means
about 300 lbs of downforce are being applied on each side of the tongue and, more importantly, that downforce is being applied only an inch or so aft of the hinge ear attachment welds. Given that without a WDH, each side of the tongue is probably carrying 250-350# of weight, the use of a WDH has likely doubled the static load on each side of the tongue to around 600 lbs, probably even more on the hinge pin side. And then if you hit a bump ...or do anything that causes an acute angle between trailer and tow vehicle (e.g. crossing a gutter)...the loading of a hitch with a WDH can easily go from 600 lbs per side to around 2000 lbs per side!
Every time the dynamic loading goes into these high ranges, the frame tube flexes a tiny bit. After many thousands of flex cycles, the metal crystallizes and eventually develops tiny cracks. Those tiny cracks gradually coalesce into a full crack.
And finally, contributing to the problem is the fact that TM fabricated the hinge pin ears using thick (roughly 3/8) steel and welded them to the much thinner (~1/8 inch thick) walls of the tongue frame tubes using a heavy welding bead. That thick bead needed a lot of heat...and that heat in and of itself helped crystallize (or embrittle) the metal of the frame tube...making it more prone to crack when subjected to the thousands of flex cycles discussed above.
Soooo, the bottom line is that factors which increase dynamic tongue loading...and concentrate the tongue loading on one side...will be the causal factors of this cracking.
That means that TMs without swing tongues
should not have any problems. It also means that tire size, lift kits, heavy axles, etc...anything that does not strongly affect tongue loading...will
not have any significant effect.
However, things that
do affect dynamic tongue loading will be culprits: use of a WDH; towing long distances over rough roads that produce substantial and frequent shock loads on the tongue; towing frequently on sharply curving mountain roads; and heavy front loads inside the trailer (e.g. 40 gallons of water).
In my case, I strongly suspect that my regular mountain towing is a significant factor, particularly in combination with use of a WDH and a fairly front loaded trailer (my tongue weight is around 600 lbs).
Hope this clarifies things.
) due to stress fractures. Nowadays I build data driven business software.
