For affirmance -- Chief Justice Weintraub, and Justices Jacobs, Francis, Proctor, Hall, Schettino and Haneman. For reversal -- None. The opinion of the court was delivered by Francis, J.
[37 NJ Page 527] Plaintiff, Margaret C. Courtois, brought this suit as guardian of her husband, Carroll E. Courtois, against defendant, General Motors Corporation, to recover damages
on account of serious head and other injuries suffered by him, which resulted in his mental incompetency. The claim against General Motors was predicated upon a charge of negligence in the manufacture of a certain tractor, and of breach of an implied warranty of merchantability of the tractor, a rear wheel of which came off and collided with a small truck being driven by Courtois. The trial court dismissed the cause of action based on warranty on the ground that Courtois was not a party to nor within the distributive chain created by the contract of sale between General Motors and the original purchaser of the tractor, and therefore could not sue for a breach of warranty arising from and incidental to that contract. In short, the injured man was regarded as a mere bystander, remote from the manufacturer of the tractor, who derived no rights from the contract of sale. The issue of General Motors' negligence was submitted to the jury, which returned a verdict for the defendant. We certified plaintiff's ensuing appeal from the adverse decision in both warranty and negligence claims before it was considered in the Appellate Division.
General Motors manufactures and distributes tractors. Between April and June 1951 it sold a new 1951 Diesel Tractor, Model 652, weighing approximately 10,000 pounds, to one Sam Coil of Washington Courthouse, Ohio. The tractor had large dual rubber-tired wheels on the rear. The wheel assembly consisted of the hub, the hub or axle flange into which 10 steel studs are pressed firmly so as to be immovable, the inner wheel disc and rim assembly, and the outer wheel disc and rim assembly. The wheels are placed so that the 10 studs project through 10 openings in the disc; then locking nuts are put on the 10 studs and tightened so as to produce a rigid, unitary assembly.
The locking nuts are tightened with a hand-manipulated wheel socket wrench, which is standard equipment for such a tractor. No one suggests that the tightening process is not easily accomplished by an ordinary individual. The "torque" (force applied) specification ranges from 260 foot
pounds to 350 foot pounds. The fact that such tightening is easily accomplished is emphasized by the Owners and Drivers Manual furnished with the vehicle, which says: "Always use regular wheel nut wrench to tighten wheel nuts or use torque wrench. Do not use an extension handle * * *." Use of an extension handle on the wrench magnifies the force applied in accordance with a scientific ratio, and the admonition against extending the handle obviously is to avoid the application of excessive tightening force to the nuts. Such excessive force, it is inescapably inferable, would have the tendency to adversely affect the threads and grooves on the nuts and studs. The warning against an extension handle is set forth in the Manual twice on the same page in different type print. Under the heading "Tightening Wheel Nuts," the following appears: "If regular wheel nut wrench equipment is used, do not use an extension handle * * *."
Tightening of the nuts anywhere within the range of 260 foot pounds to 350 foot pounds is satisfactory. Such tightening produces a high clamping force which holds the parts firmly together and causes the wheel and its associated parts to operate as an integral unit. The clamping force ranges from 18,000 to 27,000 pounds, depending on the degree of torque between 260 and 350 foot pounds that is applied to the stud nuts. That clamping force draws the wheel hub and drum into a single unit which will withstand "with ample reserve" any operational forces that may be applied in ordinary and expected use of the tractor.
Everyone conceded the importance of keeping the stud nuts properly tightened, within the range specified. A stud will break or fail only when a bending force is applied to it. If the nut on the stud is permitted to loosen (and it is undisputed that they do loosen with use of the tractor) the clamping force, which holds the wheel assembly in place as a unit, is lessened, thus allowing some foreign movement or oscillation which, in turn, permits the application of a bending force to the stud. The degree of the
bending force when the tractor is in operation, depends in large measure upon the extent of the looseness of the nut. And it is plain from the record that a nut could be loose enough to allow application of bending force to the stud without that looseness being observable on mere visual inspection. Proper maintenance requires regular testing and tightening with the standard torque wrench. If this abnormal bending force of varying degrees, depending on the looseness of the nut, is visited upon the stud constantly or at intervals during the life and use of the tractor, it will cause metal fatigue, and eventually an untimely and unnatural fracture of the stud. In other words, inadequate maintenance will cause the stud to wear out long before its time. According to one of defendant's experts, some tractors with proper maintenance have been known to last 10 years, and with such maintenance the studs should function as long as the tractor.
The importance of keeping the 10 stud nuts tight is emphasized in the Owners and Drivers Manual. It says in large type:
"WHEN TRUCK IS NEW OR AFTER EACH WHEEL REMOVAL."
"Tighten nuts DAILY for the first 500 miles of service to compensate for setting-in of clamping surfaces. * * *."
The necessity for maintaining proper stud nut tightness was fully recognized and accepted by plaintiff's principal expert. In speaking of such need whenever the wheels are removed, for a tire change for example, he said:
"Any time the entity is separated, where the two wheels have been taken from their original position and are reapplied, the roughness that had initially been compensated for by the tightening, subsequent tightening, is now reintroduced in the contact of the two members and just as in the initial production of the vehicle, the same situation again reappears and consequently must be taken into consideration by retightening after operation.
Q. In other words, proper maintenance of a truck requires that after the wheels have been removed, let us say for the purpose of putting new tires on it that when the wheel is replaced that care and attention be given to the tightening of the nuts, isn't that so?
A. Yes, sir. That's absolutely correct.
Q. And if those nuts are not properly tightened that would be an indication of improper maintenance, would it not?
A. If the nuts are not tight, yes, I agree with you, sir.
Q. And it is a requirement, isn't it, in case of a truck of this nature that when the wheels are replaced after tires are changed, let us say, that specific care and attention be given to the tightening of the nuts?
A. That's an Interstate Commerce Commission requirement, sir.
Q. And if you don't do that, what happens?
A. Well, if you don't do that, you can produce any type of failure ultimately.
A. You can produce a failure in the nuts, you can produce a failure in the wheel.
A. And in the studs, yes, sir.
Q. And why is that? Why do you produce a failure in the studs, if you don't maintain the vehicle properly?
A. If you don't maintain the vehicle properly, and you permit operation under conditions as you are now suggesting, sir, additional forces are introduced which will, and of greater magnitude than normal and these will produce failure at a much earlier period."
Defendant's expert said that when stud nuts become loose, a lessening of the clamping pressure occurs. This release of pressure permits a kind of gapping movement in the wheel assembly which may be very slight or even imperceptible. Such movement allows a repetitive dynamic bending or flexing force of much greater magnitude than normal to be imposed on the stud bearing the loose nut and that force induces and hastens metal fatigue. Thus, he asserted, there is a definite relationship between inadequate maintenance of wheel assemblies and failure of studs.
The necessity for proper inspection and maintenance of tractors engaged in interstate transportation is recognized by the Interstate Commerce Commission. Its regulations require elaborate reports by drivers of their inspection and of ...