YOUR GEARBOX.

Southland Times, Issue 21073, 3 May 1930, Page 17

YOUR GEARBOX.

HOW TO MAKE QUIET CHANGES. A CANDID TALK. If gearboxes were given the power of speech, many a man would be afraid to enter his garage to-morrow morning, for of all the parts of a ear which receive brutal treatment the gearbox is the worst sufferer. In a way, of course, a gearbox can speak. It will, on occasion, writes The Ijght Car and Cyclecar, voice its protests loud and long for all the world —as well as the driver—to hear; but many drivers, like the leaders of the Inquisition, listen without a flicker of an eyelid to sounds of distress which cause other folk with sympathetic natures acute pain. “Why should a gearbox proclaim to all and sundry its is being illtreatedgrumbles The Torturer, “Surely, in this year of grace, 1930, every part of a car should be foolproof, and surely a gearbox, above all things, should be so made that it will submite to even the most careless handling?” If the logic of this remark is accepted it gets us very little farther. The fact is that the “crash” type of gearbox is still with us and that the driver who cannot master it is not worthy of the name. Moreover, it should be emphasized that progress in design is not stagnant. Many of us remember the days of castiron outer casings, quadrant change and gearwheels which were as “soft" as they were badly machined. Before you could engage top gear you had perforce to mesh first, ' then second gear, whilst to return to neutral you had, vice versa, to “go through” second and first gears. To be able to judge the undefined neutral position, say, between top and second, when it came to double declutching'down, really did require an expert touch. Nowadays the outer casing is made of aluminium alloy—thus lightening the whole gearbox, the “gate" principle of gear selection is almost universal, gear wheels are made of high-grade steel, the teeth being ground as well as machined to fine limits, and go-ahead manufacturers are filing “silent," “constant-mesh,” or "twin-tup” gears—whichever,you prefer to call them. Just after the war one enterprizing cyclecar manufacturer, who had until then employed open dogs and chains, condensed the whole assembly, as it were, and squeezed it into the comparatively narrow confines of a gearbox, thus providing constant mesh gears for every ratio; but it was expensive, and the complete gearbox was considered too heavy. For all that, it was a delightful affair to handle, and it might have been the means of revolutionizing modern gearboxes had the concern continued to prosper—which it did not. In the sphere of light cars, gearboxes of this kind are now unknown, but in view of the progress which has been made in the use of' lighter and stronger metals designers might-well reconsider the merits of this form of construction. To get down to modern gearboxes, what are the snags which many drivers seem unable to overcome? changing up appears to present little difficulty, although, you will still hear extraordinary sounds emanating from a gearbox as some drivers accelerate away! It is the changing down business that appears to worry many drivers, who, on every occasion when it is necessary to engage a lower gear, go through a painful process usually described as “sorting them out.” Now, gearboxes differ tremendously; why, it is difficult to say in a few words, but the fact may be taken for granted. Even the veriest novice is surprised at the ease with which he can change gear on one car and the difficulty which he experiences with another; but, no matter what kind of gearbox he is dealing with, the rules are the same. First of all, remember that there is a marked difference in the way one should handle a "cold” gearbox compared with one which has been "warmed up,” by, say, 15 miles running. For example ' when making a change from first gear to second gear, - the second-gear pinion on . the layshaft must slow down to a speed approximating to that of the fellow pinion on the tail shaft if silent engagement is to be effected. When the oil in the gearbox is cold and heavy it a'cts as a brake, consequently the slowing down process is much mote rapid. Thick Oil a Disadvantage. This is probably common knowledge, but what puzzles many people is how to overcome the difficulty of making a silent change from first to second when it seems a physical impossibility to move the gear lever from one slot to the other with sufficient celerity.

Where this is the case it pointe—in the absence of a fierce clutch stop —to the obvious need for thinning down the lubricant in the gearbox. Use a clean vessel as a container and drain off the lubricant in the box after coming in at the conclusion of a run. Pour off approximate.y half of the lubricant and make it. up to its previous level with good engine oil. After this ha.'j been accomplished with a dead-cold gearbox it should then be possible to make a “straight-through” change from first to second. If despite this partial remedy, the layshaft still slows up too quickly, "double declutching up” must be employed. The procedure is simple and is as follows: — Declutch, shift the gear lever into neutral, re-engage the clutch, rev. up the engine .slightly, declutch again and shift the gear lever into the second gear notch. The trouble is usually more prounced when changing from first to second, because there is, as a rule, a greater difference in ratio between first and second than between the other ratios. As the gearbox warms up a silent “straight through” change is impossible and a pause with the gear lever in neutral becomes necessary. This calls for precise judgement so that one knows exactly when a pause will be required, and —the oil having attained the maximum degree of fluidity—exactly what pause is required in order to make a dead quiet change. Using the Engine as a Gear Brake. Many people fail to realize that this pause depends on the speed of the car at the moment the change' of gear is made. To reduce the duration of this pause, double declutching may again be employed, but with one important qualification—no use of the accelerator pedal should be made. Instead of using the engine to rev. up the layshaft slightly it is employed as a brake to slow' it down. Thus if a car be driven as fast as it will go in first gear, the clutch depressed, the gear lever moved into neutral and pressure removed from the accelerator pedal, the engine will slow down far more rapidly than the clutch shaft which, through the medium of the constant-mesh pinions drives the layshaft. To make a quick change, therefore, declutch, move the gear lever into neutral, re-engage the clutch for a period depending on the speed at which the car was going w'hen the change was made, but which is seldom more than three full seconds, declutch again and re-engage second. Some people contend that it is quicker and easier to change up without declutching. This, however, in the opinion of the writer, is open to question, for it depends so much on the skill of the operator. Changing from an intermediate ratio to top gear in this manner is fairly safe and comparatively easy, because one is meshing dogs, or their equivalent, instead of toothed wheels—the former, obviously, being easier to engage without noise than the latter. And now for the far more difficult business of changing down. The trouble with many drivers' is that they simply will not devote a few minutes’ careful thought in investigating what is going on in a gearbox and what happens when they have to change down to a lower gear ratio. They become confused by all this douole-de-clutching business which, apparently, has to be gone through when an engine is cold in one way, when it warms up in another way, and when changing down in some other manner, and, unable to sort out their thoughts, they continue to sort out their gears! A great deal more might be written about the use and abuse of gearboxes, but enough has been said, it is hoped, to divert the perhaps chaotic thoughts of the novice along an entirely new line of reflection.