CARING FOR THE CLUTCH OF THE AUTOMOBILE

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Clarence Nash
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602 THE OUTING MAGAZINE CARING FOR THE CLUTCH OF THE AUTOMOBILE BY HAROLD WHITING SLAUSON HE clutch is one of the most important parts of the automobile and yet one which probably receives less

1 602 THE OUTING MAGAZINE CARING FOR THE CLUTCH OF THE AUTOMOBILE BY HAROLD WHITING SLAUSON HE clutch is one of the most important parts of the automobile and yet one which probably receives less attention from the owner or driver than any other portion of the mechanism. The valves will be ground, the cylinders freed from carbon, the ignition system adjusted and the differential and transmission cases cleaned and refilled with fresh lubricant while the clutch remains untouched, and yet it is expected to do its share of the work without, literally, so much as a murmur. It is to the credit of the average well-designed clutch that it does not require attention in proportion to the amount of work that it performs, and some may be almost neglected for thousands of miles without being damaged seriously. The clutch, however, should not be kept in condition for its own sake alone, but for that of the motor, transmission and tires as well, for upon its proper operation depends the amount of strains and shocks that will or will not be imparted to the remainder of the power plant and running gear. The purpose of the clutch is obvious to anyone who has ever driven a car, for he realizes that it would be impracticable to stop the motor each time the automobile stops and yet this would be necessary were there no mechanism by means of which the one may be disconnected from the other. Furthermore, a gasoline engine cannot be started "under load" and consequently the rear wheels which drive the car must be disconnected from the crankshaft of the engine so that the latter may be allowed to run "free" during its first few revolutions. In addition to these reasons, the gears of the sliding transmission cannot be shifted and the various speeds obtained unless the motor is disconnected while the change is being made and thus the clutch will be used much more than will the brakes or the gear shift lever. Of course, the motor is generally cranked when the transmission is in the neutral position, in which case the clutch may be left engaged, but the gear change could not have been made without first disconnecting the crankshaft and consequently it may be said that the use of the clutch must always precede the starting of the engine. The work that the clutch is called upon to do precludes the use on an automobile of what is really the simplest type, the complications in design being necessary because of the fact that the load must be applied gradually. A positive clutch, such as one of the jaw type, is strong and simple in construction, but is unsuitable for use on an automobile because the load cannot be applied while

2 CARING FOR THE CLUTCH OF THE AUTOMOBILE 603 the motor is in motion. In other words, there is no "half-way" position for the positive clutch and the entire load must be either on or off. It is evident that the sudden application of a maximum load to a motor that is running would be disastrous in at least two respects: the engine would be brought to an abrupt stop or "stalled" and the attendant strain and shock that would be transmitted to the gears, shafts and tires would cause serious damage. Consequently any form of positive clutch is out of the question for use on an automobile and designers have almost universally turned their attention to the friction type, in which the load is "taken up" slowly by the gradual increase in pressure between two rubbing surfaces. If the clutch is so constructed that this pressure or friction may be regulated by the driver, the load may be applied or removed as gradually as desired and the strain on the motor and running gear will thus be reduced to a minimum. No matter what type of clutch is under consideration and there are many it must consist essentially of two parts, one of which is positively connected to the end of the crank shaft of the motor and revolves with it, while the other is attached to the driving shaft through the medium of the transmission. The portions of these two parts which come into direct contact with each other have special friction surfaces which receive the greater part of the wear of the clutch. These rubbing surfaces of the clutch are normally held in contact by means of a stiff spring and are separated only by the movement of a pedal or a side lever. When the friction surfaces are in the proper condition, this spring is sufficiently stiff to hold the two parts of the clutch so tightly together that no slipping will take place and the crank shaft and driving shaft revolve together as a unit in the same manner as though they were connected by means of a positive coupling. When the two portions of the clutch are moved apart so that no contact between the friction surfaces occurs, the clutch is said to be disengaged and the motor may revolve independently of the transmission. If the lever or pedal which disengages the clutch is released slowly, the spring will gradually force the two parts together with increasing friction until, finally, the entire load is applied and the portions of the clutch are revolving as a unit with no slipping taking place. Of course, when the two parts are first brought together, slipping must take place until the motor has "picked up" the load, but it is this very flexibility of the friction clutch that makes it so well adapted for use on motor cars on which a positive clutch would be an absolute failure. The nature of the friction surfaces of the clutch is an important consideration, and substances must be chosen for the rubbing contact which will have a sufficiently high "coefficient of friction," or "grip" upon each other, and yet which will be able to withstand the immense amount of heat generated by the slipping. Leather has proved to be a tried and true friend of the clutch designer, and it has been used as a friction surface as long as the gasoline automobile has been on the market. On the "Cone" Clutch It is on the common form of clutch known as the "cone" type that leather forms the friction surface, and it has been found that aluminum or cast iron makes the best companion rubbing surface. The leather, of course, is only a covering which is riveted to a disc having a beveled periphery, thus giving it a shape similar to that of a thin frustum of a cone. This portion of the clutch is mounted on the forward end of the transmission shaft by means of a "feather key" or square shoulder that causes the two to turn together and yet enables the cone to slide longitudinally for a short distance. The second member of the clutch is mounted on the rear end of the crankshaft of the motor and consists of a disc having a recess in its face into which the cone will fit tightly. That is, the sides of the circular recess in the second member are cut at an angle corresponding to the bevel of the periphery of the cone, and thus when the two parts are forced together by the

3 604 THE OUTING MAGAZINE spring, the first portion fits "flush" into the second and the entire leather surface is in contact with the aluminum or cast iron sides of the recess. It will be seen that the cone-shaped parts constitute a wedge-like action which enables the leather to grip the second surface with a force of friction almost equal to that of a positive clutch, and yet by withdrawing the cone member a certain amount, the pressure is reduced and any degree of slipping can be allowed to take place. This action, of course, is reversed when the clutch is first engaged, for the leather comes into contact with its friction surface gradually and slowly reduces the slipping until the two parts of the clutch are finally revolving as a unit. There are two extremes of clutch behavior, neither of which is desirable. As in many other cases, it is the "happy medium" from which the best results will be obtained, and as this depends upon the condition of the friction surface, the attention to the leather of a cone clutch is an important matter. These two undesirable extremes of clutch action consist of slipping when the parts are fully engaged, and of the harsh and sudden seizing of one member upon the other. The one is caused by too smooth or greasy a leather, while the other trouble may be laid to a friction surface that is abnormally rough. On account of the friction and the attendant heat generated in a clutch, the leather must be properly lubricated, but an excess of oil will be as productive of undesired results as will an insufficient supply. The man who drives a car will become accustomed to a certain relation between the sound of the motor and the speed of the machine. When the motor appears to be running faster on the "high" than the speed of the car would seem to warrant, it is evident that the clutch is slipping, for this is the only portion of the mechanism in which there is not a positive connection between the moving parts. As was stated in the preceding paragraph, this slipping will probably be due to an excess of lubricant and is a condition that may exist even though no more oil than that called for by the instructions is applied to the clutch. Leather is more or less absorbent, and the continued application of oil will gradually saturate the substance until the clutch can no longer "hold." If the leather is not badly worn when slipping first begins to take place, a small amount of rosin judiciously applied to the surface may remedy matters, but care should be taken not to administer an overdose, or a "harsh" clutch will result. Just before the rosin is applied, it is a good idea to remove the excess oil from the surface of the leather and the sides of the recess of the second member. If gasoline is used in this cleaning process, enough of the excess oil possibly may be removed to render the application of the rosin unnecessary. When to Replace the Leather Owing to the wedge action of the cone when it fits into its recess, the wear of the leather is, to a certain extent, taken up automatically. Continued use, however, will so reduce the thickness of the leather that the cone may be forced as far as possible into the other member without the application of sufficient pressure between the friction surfaces, and in this case, the old leather will need to be replaced with a new piece. This is not a difficult operation, but if it is done by the amateur, he will need to exercise great care in cutting the leather to exactly the proper size and shape so that it will fit smoothly and snugly throughout its length and width. The rivets that hold the leather in place should be countersunk so that their heads will set well below the surface and will not come in contact with the second member of the clutch. A slipping clutch may sometimes be cured temporarily by tightening the spring that holds the two parts together, but this is only a makeshift, for the fact that the clutch slips at all is generally conclusive evidence that the trouble lies with the friction surface. Annoying as is a slipping clutch, one that is "fierce" is a greater evil, for it can do serious damage to the motor and running gear, as well as make riding exceedingly unpleasant for the occupants of the car. A clutch of this tempera-

4 CARING FOR THE CLUTCH OF THE AUTOMOBILE 605 ment cannot be engaged gradually but will "take hold" suddenly and with a viciousness that will not only jerk the car but will strain the motor and running gear, as well. In such a case, care on the part of the driver is of little avail, for no matter how gingerly he may release his foot from the pedal, the harsh friction surface will grip rigidly almost as soon as the contact is made between the two parts of the clutch. If it is a cone clutch that is giving this trouble, it is probable that the leather has become too dry. If the heat of friction has not abraded the surface too severely, the action of the clutch may be improved greatly by the application of a small amount of castor oil to the leather. This should be distributed evenly and worked in by operating the clutch a few times while the motor is running. Neatsfoot oil may also be used as a cure for a "fierce" clutch. Whichever oil is used, however, care should be taken to apply it sparingly, as an excess will cause the clutch to slip. In order to make the contact between the two parts more gradual, some clutches are designed with small springs set at frequent intervals under the leather. The leather is forced out in the form of a small "hump" over each spring, and these protruding surfaces first come in contact with the second member of the clutch when the pedal is released. Thus it will be seen that the area of the friction surface increases as the pressure against the cone becomes greater. The layman would not expect cork to form a good friction surface for use in a clutch, and yet this substance possesses properties that render it exceedingly well adapted for such purposes. Its "co-efficient of friction" is high, which means that, with sufficient pressure, it can obtain a good grip upon its companion rubbing surface. In addition to this, cork is compressible and will stand a high degree of the heat of friction without becoming harsh or injured in any other way. These properties are used to good advantage in the "cork insert" clutch. Such a clutch may be of the leather- faced cone type having corks set into the periphery at frequent intervals. These corks project about 1/64 of an inch above the surface of the leather and are consequently the first portion of the cone to come in contact with the second member when the clutch is engaged. The cork surface will withstand the friction and heat of the attendant slipping, and thus somewhat the same effect is obtained as though the small springs were used under the continuous leather covering. As the push of the main spring against the cone increases, the corks are compressed until they are flush with the surface of the leather and the entire area of the cone is in contact with the second member of the clutch. This cork and leather surface has been found to be very efficient in transmitting the power from the motor to the running gear of the car. The Use of Cork Inserts A cone clutch provided with cork inserts will probably not need as much oil as will one of the full leather type, as the cork surface will withstand a surprising amount of wear and heat. The renewal of the leather will be somewhat difficult, however, as the holes must be cut to "register" exactly with the recesses in the cone casting. The renewal of the corks should not be necessary, even after thousands of miles of use, but if any should become unduly worn, they should be replaced at the factory or at a shop at which the services of an expert can be obtained. The corks are forced in place under great pressure and are cut accurately so that exactly the proper length will project beyond the surface of the leather. Anyone familiar only with the construction of the cone clutch would scarcely recognize in the disc type a mechanism that serves the same purposes. Different as is the construction, however, the principle of the two types is the same as both rely on the friction between two surfaces to regulate and carry the power from the motor to the transmission. Instead of the cone and recessed member into which it fits, the disc clutch consists of a series of flat

5 606 THE OUTING MAGAZINE plates, alternate ones of which are attached to the end of the motor crankshaft, while those between are fastened to the driving or the transmission shaft. Thus there are two sets of "interlacing" plates, and as the individual members can slide independently for a short distance along the shaft to which they are attached, the entire series may be either compressed or separated. It will be seen that if these plates are held closely together by means of a heavy spring, none will be allowed to turn independently, and consequently the two sets will revolve as a unit and will form a continuous connection between the motor and transmission. If the pressure between these plates is released slightly, slipping between the individual members of the two sets of discs will take place, and when all pressure is removed, the motor may revolve without communicating motion to the other half of the clutch. Material for the Clutch Discs There are several materials of which the clutch discs may be composed. A common practice is to construct one set of discs of a certain material and to use for the other set a different substance but one that possesses the proper frictional qualities when moved in contact with the first. Thus, all of the discs attached to the motor crankshaft may be composed of a special bronze or copper composition, while the plates with which these come in contact and which are fastened to the transmission may be of steel, aluminum, or whatever other metal gives the best results. In some forms of clutches there may be but three or five discs, while others may contain nearly fifty plates. Practically all of the "metal to metal" disc clutches are contained in an oiltight case which should be kept partially filled with a lubricant of the proper quality and consistency. The lower portions of the discs consequently revolve in oil, and this lubricant is carried to the entire surface of each when the clutch is disengaged. As the clutch spring is released and the discs are forced together, the oil is gradually squeezed out, and thus the nature of the friction surface is changed automatically at the same time that the pressure increases. A clutch of this type will wear but slightly and it is seldom that a new plate will be required. The clutch should be taken apart and cleaned every few thousand miles, however, and the old oil and grease replaced with new, clean lubricant. Any gummed oil which adheres to the plates should be removed with gasoline or kerosene, for if this is allowed to remain, the friction surface will be so changed that the clutch will slip, and tightening the spring will not remove the cause of the trouble. The plates of a metal-to-metal disc clutch may, after a long period of use, be worn more in some places than in others. When the discs are examined all rough surfaces should be smoothed down with a file or coarse emery paper, for abrasions will not only wear the adjoining discs, but will make the action of the clutch harsh and difficult to control, as well. It is probable also that the edges of some of the discs will be turned over or worn rough, and this condition will often cause the clutch to stick so that it cannot be disengaged easily. This is a bad fault and may sometimes result in accident to car and occupants if the trouble is not remedied. The cure is simple, however, and if a file is used on all of the plates that show any sign of roughness, even to the extent of beveling the edges slightly to make certain that all ridges and projections are removed, the clutch can be made as good as new. Some forms of disc clutches employ steel plates that revolve adjacent to "cork inserts" in the second set of discs. In this case, of course, the cork insert plates take the place of the copper or bronze composition discs described above, but otherwise the action of the two types is the same. There are also other combinations of discs, such as steel against a specially treated steel, steel against fiber compound, and steel against an asbestos preparation. Some of these forms are known as "dry plate" clutches for the reason that they require no oil, but such a type, of course, demands the use of the very high-

6 CARING FOR THE CLUTCH OF THE AUTOMOBILE 607 est heat-resisting materials obtainable. Although the dry-plate clutch gives better service when run without oil, it is possible that the owner of such a type, despite directions to the contrary, will endeavor to lubricate the plates. No serious damage will result from this mistake, however, as nearly all of the dryplate clutches are provided with channels in the discs which will allow the lubricant to flow to the bottom of the case, from which it may be drained as soon as the driver discovers his mistake. The "floating ring" clutch is similar in principle to the types just described, except that a single ring replaces one set of discs. There is another type of clutch, however, which is quite different from either the cone or the disc form. This consists of a cast-iron, steel, or aluminum rim attached to the rear end of the crankshaft of the motor. This rim, or drum, revolves near a band or shoe that can be made to clamp the moving surface and thus turn the transmission with the motor. In one form, a spring operates a series of levers or racks which expands, or moves outward, a jointed shoe around which the rim revolves. This shoe is generally of brass or bronze, and as it grips the interior of the rim with a constantly increasing pressure when the pedal controlling the spring is released gradually, the two portions of the clutch finally revolve as a unit. This is known as the "internal expanding" type. The "external, contracting clutch" operates on somewhat the same principle as the type just described, except that a band surrounds the outside of the drum, or rim, and can be made to constrict until a sufficient grip is obtained to cause the two parts of the clutch to revolve as a unit. This constricting band may consist of a strip of flexible steel to the inside of which is attached a speciallytreated fiber or canvas which possesses the proper frictional and heat-resisting qualities. The amount of oil necessary on either the expanding shoe or the constricting band type of clutch depends upon the nature of the materials used as friction surfaces, but it may be said in general that neither of these forms is intended to be run entirely "dry." If undue wear takes place in either the band or the shoe, the part may be replaced easily, as one of the main features of design of this type of clutch lies in the accessibility of all portions. Adjusting nuts and screws are provided by means of which a certain amount of wear may be taken up. No matter how well-designed and smooth-acting a clutch may be, the personal equation enters largely into its operation, and, if not handled properly, the most perfect mechanism of this kind may give results no better than those obtained from an old and worn out clutch. The ordinary friction clutch is not automatic and the controlling pedal must never be released suddenly when the motor is running. A sudden engagement of the clutch may, at the time, seem to do no more than cause the car to "rear up on its hind legs," but strains will surely be induced in the motor and running gear that will eventually make a worn-out machine of one that should, if properly used, give several more years of active service. Furthermore, continued abuse of the clutch may serve so to strain the shafts that the two members will be thrown out of alignment, thus preventing a uniform distribution of the friction and pressure. This may result in a "jammed" clutch, or one which cannot be disengaged, and it is evident in such a case that the driver will be unable to control the car properly and that the passengers and machine are in great danger if the automobile is run under these conditions. Although rare, such accidents have occurred a sufficient number of times to render a warning of this kind worthy of notice on the part of the carelessly-inclined driver.

MANUAL SHIFT AND AUTOMATIC TRANSMISSIONS

CHAPTER 17 MANUAL SHIFT AND AUTOMATIC TRANSMISSIONS The vehicle driver must be prepared to drive vehicles with either manual or automatic transmission. Each transmission type requires specific methods