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Look after your trailer
Page 86
Page 87
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THE man who says "There's nothing to a semi-trailer; it's just a platform and some wheels" wants his head examined. Yet you do hear such talk. Even where you don't hear it, you see its implications in practice. All over the country operators can be found—including some of the biggest and most experienced—who run trailers on and on, despite urgent pleas from the engineers to be allowed at least to introduce it to a grease gun!
Howeyer, I am not going to preach this particular sermon, but will concentrate on a few basic, but so often overlooked, home truths.
A new semi-trailer has just the same need for running-in attention as its motive unit; but, unhappily, it rarely receives this attention. It has no oil, fuel or water to leak and few other features of mechanical sickness that readily indicate the need for attention, yet this missed initial service can be the cause of mechanical trouble at quite an early date.
From this neglect can spring loose axles that permit outof-line running and premature tyre wear. Dry suspension pins, bushes and trunnions can seize solid unless given early attention, and can tear and destroy supporting chassis members. Screw landing gear on the single-axle models is right in the path of water and road debris, literally shot blasted up from the motive unit wheels; with good-fitting, but dry worm shafts or spindles, early difficulty can be experienced in lowering or raising the landing wheels.
Watch New Trailers Therefore, during the first few weeks in the life of a new trailer, regular attention should be paid to all nuts and bolts, particularly spring U-bolts and suspension beam brackets. Special attention should be given to lubrication—not just the items fitted with grease nipples, but all working parts. All too often a brake-arm clevis pin can begin to grip and cause that brake arm to hold on and, with the driver completely unaware of trouble, brake linings, oil seals and even brake drums can suffer.
These last comments indicate only a sensible approach to the needs of new equipment and may appear elementary to the engineer; yet it is sad, but true, that new trailers rarely enjoy the service given the new rigid or tractor unit. The only grease offered will be to the turntable plate, and this in the main is passed up from the tractor plate.
Rubber and air suspension are easing the engineer's burden, although stabilizer or torsion bars come in for some rough use. Where neglected, with no one taking care of adjustments. rear-bogie assemblies can float about and become heavy on tyres. All this can happen (and in a short while, too) where a trailer is put to work on common user services and, whilst of new appearance, it will receive little sympathy from the user. All too often his comment will be: "What is there to go wrong on a new trailer?"
A maximum-capacity twin-axle semi-trailer is equipped much the same as the eight-wheel rigid, rearwards of the cab, less transmission, of course. This fact has some little bearing on the dry state of linkages and other moving parts on the trailer, there being no flung-up grease or oil from transmission parts to even slightly assist lubrication—and this does matter, however slightly.
The Grease Goes Look under any eight-wheel chassis and most parts will be seen to have a coating of grease or oil; however dirty, this is at least a form of lubrication. On the trailer there is no protection whatever, and a single trunk run on a really bad night can remove all grease from shackles, links, pins, brake camshafts, and so on. Similarly, certain air motors are mounted and angled in such a fashion that water can gain entry via the rubber cover or boot once the slightest wear has taken place at the rod entry aperture, and in a short while rust or corrosion will affect braking effort. Certain rubber bushes move with their rod as intended, and all is well, others slide on the rod and unless given attention there is wear soon in evidence.
Despite the high pressures, there is still a need regularly to drain air tanks of collected water. This receives little thought on semi-trailers. Also it is not true, as some still insist, that air exhausted during braking takes all water with it; frequent draining is necessary and each piston-type air cylinder should be periodically drained and lubricated. When it is neglected for long periods it can be found on many occasions that the operating surface of an air cylinder is scarred and corroded; when cleaned it will not accept a new piston washer. Again, on diaphragm models— despite their undoubted reliability—water is a deadly enemy.
In the main, there is little trouble expected from the hubs and bearings themselves. Once grease-packed and set up correctly, they give a long, trouble-free life and can fail only because of such things as overheated brakes and lost lubrication or complete collapse caused by slack wheel nuts, with eventual stud and hub break-up. Brakes, however, are another matter and should not be permitted to operate until large clearances exist between lining and drum, as the slam of take-up can be of sledge-hammer proportions. This can be the last straw to a hot drum; also, brake anchorage at the back plate can be shocked and suffer accordingly.
Hand-operated parking brakes are a problem, as the law requires that an independent parking brake must be fitted and be capable at all times of locking the wheels to which it is coupled. This is quite apart from either the hand air control to trailer wheels from the cab, or the action of the trailer air system itself on the brakes when below pressure or uncoupled from the tractor.
The main feature of the problem is the actual hand lever and its rod or cable. Apart from the damage caused to the lever by people using it as a foot step to climb on the trailer, cable stretch or neglected adjustment can soon cause the lever to move right through its operational radius, Without moving the brake shoes.
Unhappily, there is a feature here that tends to withdraw the driver's attention from the actual effectiveness of the hand lever parking brake, and this feature is well worth a mention. A driver coupling up to a strange trailer will automatically pull on the trailer handbrake, and then give rarely the cause of a dropped trailer, as this equipment is mounted on the tractor, leaving only the standard pin to face the hazards of common user activities—and this pin can really take punishment!
To return to the coupling, little more than regular lubrication is required to keep it fit, although it is good practice periodically to wash and thoroughly dean the whole turntable and its mechanism underneath, and then re-lubricate. This takes care of the grit and road debris that could possibly interfere with the jaws and sliding parts. By far the greater problem on the tractor is the security of the coupling assembly on the chassis as, with regular use. bolts will slacken and bearers can crack at points of connection to the chassis.