One single 1” diameter (or maybe 1-1/8” if we’re lucky) draw pin at the tractor carrying all the weight behind it with 3 more draw pins (one on each wagon) carrying progressively lower loads. How strong is that pin? Just like bolts, hitch pins have grades. A 1” diameter grade 5 pin will shear under a load of 38,500 lbs – meaning if you were to hang 38,500 lbs from the pin, it would break. When towing, you aren’t carrying the entire weight on the pin, but it’s still a good gauge for the load limit. Consider the added stress on the pins when you jerk the load on start-up or jam on the brakes in an emergency. AT MINIMUM, for this load, a 1.5-inch, grade 8 pin should be used at the tractor (shear strength of 122,000 lbs) if it will even fit the running gear of these 400 bu wagons. And that is for certified graded pins! A home-built pin? Don’t even think about it!
The stress on that pin at the tractor depends on the weight of the load, the speed of transport, the stress of the braking force applied, and the amount of contact of the pin to the tongue and drawbar. The wagon hooked to the tractor has the weight distributed over two thin (the tongue hitch) and one thick (the tractor drawbar) contact points. The wagons behind have 3 thin contact points, two on the tongue of the following wagon, and a hitch plate on the forward wagon. Yes, they tow less weight but the thin steel of the towed trailers hitch plate has a greater chance of breaking or twisting under load.
What about safety chains? The chain at the tractor must be of a grade/capacity to carry the entire load. The chains put on wagons by the manufacturer are rated for the capacity of a single wagon (maybe two wagons if you’re lucky). Have you upgraded your chains so that each wagon in the train has a chain sized for the capacity of that wagon and the wagons attached to it? Likely not! But we shouldn’t have to ask this question because no one in their right mind should be thinking of pulling such a load, RIGHT? If the hitch or pin breaks on any one of the wagons, will that loose wagon(s) follow straight being towed by only the chain, or is it going to jackknife?
The vast majority of wagons do not have brakes. Bigger wagons may be equipped with surge brakes. But you have no control with surge brakes until the weight comes forward during braking. You have no way to engage the wagon brakes to start braking the load to correct potential jackknifing or start to stop the entire load. There is a high potential that the wagons will jackknife as they all surge forward during panic braking. Think also about not having enough tractor power to pull the load. If you run out of power for this load going uphill and stall, it is highly unlikely that the tractor brakes will be able to hold the load. The whole thing will slide backward and jackknife with potentially devastating consequences.
Wagon manufacturers have commented that the only brakes they support are the hydraulic brakes hooked to the tractor system, or even better those hooked to a receptacle in newer tractors that connect the wagon brakes to the tractor brake pedals, enabling them to be set to engage when the operator initiates braking. Many people opt against the brakes because of cost on the assumption that their big tractor can control the load. THINK AGAIN!
What is a safe towing speed? If you come to the field empty at full road speed, is that the same speed you should be pulling a full load at? Obviously not, but what is your practice? Consult your equipment’s Owner’s Manual for information on safe travel speeds and weight limits.