The automobile owner's guide

The clutch used in automobile construction of the present day becomes a necessary part of the equipment upon the adoption by manufacturers of the progressive and selective types of sliding gear transmissions.

When the engine is started the clutch is “in,” that is, in contact with the flywheel, and all parts of the clutch revolve with it at the same speed. The shaft on which the clutch is mounted extends into the transmission gear case, but as the transmission gears are in a neutral position, the movement of the car is not affected.

When the car is to be started the clutch foot pedal (usually on the left side of the steering column) is pressed down. This throws the part attached to the drive shaft out of contact with the part attached to the flywheel, and in its backward movement it comes into contact with the clutch brake, as shown in Fig. 105, which stops it from revolving. The hand gear control lever is shifted into the first speed slot or position. The pressure on the foot pedal is then gradually released and the clutch is carried in by spring tension, and the car moves off at first speed.

Second Speed.—The clutch is thrown “out” after a brief lapse of three to five seconds has been allowed for the brake to slow up rotation in order that the gears to be meshed will be rotating at the same speed. The hand control lever is now shifted into the second speed slot, and the clutch pedals released.

High Speed or Direct Drive.—The clutch is thrown out and a few seconds allowed for it to slow up. The hand control lever is shifted into the high speed slot, which connects the drive or propeller shaft directly to the clutch shaft and the car is driven at crank shaft speed when the clutch is let in.

Reverse.—The clutch is employed in the same manner. However, the motion of the car, the clutch and all gears must be at a stand still before the gear control lever is shifted to the reverse speed slot, as the gears in the transmission operate in the opposite direction.

OPERATION

A clutch always consists of two parts, one part which is attached to the flywheel, and another part which operates on or against the part formed by the flywheel.

While there are five to seven different types of clutches, but two types are used by the majority of automobile manufacturers. The single or multiple disc clutch is used almost exclusively in unit power plant construction, while the cone type is used when the transmission is carried in a separate unit.

Fig. 105 shows the cone clutch with its three adjusting springs and clutch brake. The cone is shown in a lighter color than the flywheel. It has a funnel-shaped surface with a slant or angle of from thirty to thirty-eight degrees. The slanted surface is faced with leather and fits into the rim of the flywheel which has been ground to the same slant. The cone clutch is not attached to the flywheel but forms a part and revolves with it when the faces are in contact. The cone is carried on a separate short shaft which extends into the transmission case. This shaft carries a steel plate or disc at the front end to which the cone which slides on the shaft is anchored by studs extending from the plate through the cone. The studs usually number three or four and carry a two to three inch spring on the outer end back of the cone. The cone is backed out of contact with the flywheel face, against the tension of these springs, in a toggle leverage connected to the foot pedal. The clutch brake shown in Fig. 105 is adjustable and makes contact with the rim of the cone retarding the rotation when the cone is drawn out of contact with the flywheel.

Cone Clutch Care.—The leather face of the cone should receive 5 to 7 drops of Neat’s foot oil every thirty days. A grease cup will be found on the cone which provides lubrication for the shaft on which the cone slides. This should be given a half turn every second day.

Cone Clutch Adjustment.—The three studs extending through the cone, have a lock nut adjustment on the outer end, and the cone may be adjusted up to make a stronger face contact by loosening the lock nut and turning the inner nut to the right. This strengthens the spring tension and causes the contact faces to set more firmly. This adjustment, however, should take place only when clutch slipping is noted. Only a little movement of the nuts is necessary, and all three or four nuts should be taken up a like amount in order to prevent the cone from running out of line or making uneven contact.

Fig. 106 shows the multiple disc clutch used almost exclusively in connection with the unit power plant. This type of clutch consists of a set of plates attached and driven by the flywheel, and another set of plates or thin discs attached to the drive shaft. The drive shaft plates operate between the flywheel plates. The contact is frictional and the plates are held together by spring tension.

BORG AND BECK CLUTCH

The new Borg and Beck Clutch is provided with a thrust bearing at the inner end of the clutch sleeve, which does away with the friction between the parts, and eliminates the need of a clutch brake.

The clutch is mounted in the customary way in a housing which contains both the flywheel and the clutch.

Referring to the sectional view, Fig. 107, the action of the clutch is clear if it is kept in mind that among the rotatable parts only the driven group, comprising of the disk A and the shaft B, can stand still when the flywheel is running. All the other rotatable parts are anchored to the flywheel, and must revolve and drive with the latter. The clutch brake was formerly mounted at the inner end of the clutch shaft, and has been replaced by the thrust bearing shown at C.

When the clutch is disengaged there is no friction between the shaft B, and the throw out sleeve D. The thrust bearing takes the rotating drag of the clutch shaft, thereby eliminating the necessity for a brake to check the spinning action. The friction and power action is readily understood as, when the clutch is thrown in, all the rotating parts are friction locked into a single combination and revolve as one with the flywheel.

The power of the release clutch spring E, acting through the throwout-collar F, and the bell crank pivot G, drives the thrust shoes outwardly with a lever wedge toggle combination of powers against the overhanging, inward beveled face to the thrust ring H, since the parts on which they are mounted are backed against the cover wall or rigid end of the clutch casing. It therefore follows that the full part shafting effect of the thrust is communicated to the thrust ring H, and the latter, in being driven hard toward the flywheel, sets up between itself and the inner casing wall a friction grip sufficiently powerful to stop the slippage of the asbestos rings upon the polished faces of the discs, thus giving the drive to the car.

When the pedal is depressed to release the clutch, the retracing parts telescope the coil of the spring E, until it occupies nearly a single plane. The withdrawing parts also release the clutch shoes a sufficient distance from the face of the thrust ring H to permit the latter, together with its companion friction ring, to back away from the disc, thus breaking the friction grip and permitting it to come to a stop, while the flywheel and the parts of the clutch anchored to it are left free to revolve idly.

The release disc A is so light that its spinning does not continue except for a very short time and does not offer any clashing action on the gears. The full thrust of the spring transmitted through the powerful lever toggle action to the friction grip parts is always sufficient to lock the driving flywheel parts, and the driven disc, into a fixed nonslipping relation for a full driving action; but it is still always within control of the driver, through the foot lever, to let the clutch into engagement by degrees, and thus by a gradual increase of the friction grip, gradually overcome the starting slippage.

Adjustments.—Taking up adjustments are provided by means of bolts acting through adjustment slots in the cover. When the bolts are loosened and shifted in their cover slots, they control and shift with them an adjustment ring which brings all the shoes to new seats against the nonslipping thrust ring and these seats being farther up the inclines of the tapered ring, the ring is necessarily thrust much farther toward the other friction parts, thus compensating the wear.

The adjustment for throw-out can be controlled by taking up the friction grip adjustment, the latter being identical with the take up adjustment just described, as these too are taken care of by the same mechanical means to make the adjustment on the clutch.

Disc Clutch Cleaning; Dry Plate.—Dry plate clutches do not require any oil, except that the grease cups (which provide lubrication for the sleeve shaft and bearings) be filled weekly and given a half turn every second day. The housing and plates should be cleaned whenever slipping becomes noticeable. To do this remove the cover from the housing, and the drain plug from the bottom, hold the clutch out, and squirt kerosene over the plates with a dope gun. This will remove the grease from the plates, and also any dirt or grit that may have lodged in the bottom of the housing.

Disc Clutch Cleaning; Wet Plate.—The wet plate clutch is cleaned in the same manner as the dry plate, except that the plug is first removed from the bottom of the housing and the oil drained off before using the kerosene. After the plates and housing have been cleaned, replace the drain plug and fill the housing up to the clutch shaft with a heavy cylinder oil.

CONE CLUTCH CLEANING

Cone clutches are always in perfect condition when leaving the factory and should not require any further attention during the first season or for eight to ten thousand miles of service.

After that it is usually necessary to replace the leather, or reline the cone, which makes it as good and as serviceable as when it was new.

New Clutch Leathers.—New clutch leathers may be obtained from the manufacturer, or from the service station, by giving the number and model of the car. New clutch leathers obtained in this way are cut, shaped, and have the ends cemented, and are ready to be slipped on or off, over the cone and riveted into place. However, the leather must first be soaked in water or Neat’s foot oil to make it soft and pliable. This allows it to be driven or stretched over the cone. The rivets must be counter-sunk to prevent the heads from extending above the top surface of the leather, which would cause the clutch to “grab” or jerk upon being engaged.

Measuring and Cutting Clutch Leathers.—Whenever possible it is advisable to purchase clutch leathers cut and cemented, ready to put on. But in case of emergency or when the proper size cannot be obtained, a new leather may be cut from a piece of leather three-sixteenth of an inch in thickness using the old leather as a pattern. But in case the old leather is not available to serve as a pattern, proceed in the following manner which is illustrated in Fig. 108, which shows how to make an exact pattern out of paper without going into technicalities. Take a piece of heavy wrapping paper, forty or fifty inches long and twenty inches wide, lay the cone on the left hand edge about one inch from the bottom of the sheet, roll the cone keeping the paper flat on the face until the starting edge meets the sheet, hold the wrapped cone and draw a line around the inside of the paper, letting the pencil rest against the edge of the large diameter of the cone; repeat at the small end of the cone, then draw a line parallel to the starting edge where it meets the sheet. This will give you a pattern similar to that shown with the dotted lines in Fig. 108.

Now secure a piece of unstretchable leather (belting is preferable). This belting or leather should be slightly longer than the pattern you have just completed and sufficiently wide to embrace the curve; about twelve to fifteen inches wide for the average clutch will be sufficient, and about three-sixteenths of an inch thick.

Cut out the paper pattern and lay it on the leather belting as shown in Fig. 108, and cut out with a sharp knife, leaving one-half inch over at each end as a safety measure and for mitering the joints. Fit this leather to the cone and cut the ends the exact size, miter the ends and cement with a good leather cement. Be sure that you have the rough or flesh side of the new facing on the outside; rivet it firmly in place and smooth down the rough spots with a piece of coarse sand paper, clean off all dirt, grease, and grit, especially the grit from the sand paper, as this will grind and score the smooth surface of the flywheel and cause clutch slipping. Paint the leather with Neat’s foot oil and the clutch is ready to be assembled and adjusted.

Cone Clutch Cleaning.—Cone clutches usually do not require any special care or cleaning unless oil or grease, other than (Neat’s foot or castor) are applied accidentally or by mistake to the leather face. If this happens the grease must be thoroughly cleaned off of the leather face with kerosene or gasoline otherwise the clutch will not hold. After the clutch leather has been washed allow it to dry for twenty minutes and apply a thin coat of Neat’s foot oil evenly on the leather face before reassembling the clutch.