« НазадПродовжити »
B-25 Buick cars. It is of the leather-faced cone type, having three plungers pressed against a leather facing by coil springs to make for easy engagement. The construction is clearly shown in the accompanying sectional view, which also points out the portions needing lubrication. Of these, the clutch spindle is lubricated by a grease cup carried by the clutch cone, while a pipe plug is placed in the spring housing to introduce grease for the thrust bearing. In this clutch the spring tension may be increased by screwing in the threaded nut on the end of the crankshaft extension. The clutch cone is of aluminum and is tapered in the usual way, having a standard angle of 12/2 degrees. The cone is held in engagement with the flywheel by the large coil spring enclosed in a housing member, that also serves as a clutch cone carrier. At the rear of this sleeve or housing member is placed the coupling which connects the clutch with the primary shaft of the change speed gearing. The housing carries a collar connected with the clutch pedal, so that when that member is depressed the clutch spring is compressed and the cone pulled away from the flywheel rim. After the clutch has overcome the inertia imparted by the flywheel it remains stationary when released, the crankshaft extension rotating freely inside of the clutch spindle bearing.
The most common cause of faulty clutch action is some defect of the leather facing, as this way be packed down hard or charred by heat from slipping, or it may have been used so long that the leather has lost its life and become hard, with a glazed surface that has a very low degree of frictional adhesion. The clutch spring may have become weakened or broken ; this will cause the clutch to slip, even if the leather facing is in good condition. The two troubles usually met with are harsh action as one extreme condition and power loss because of slipping as the other. If the surface of the leather lining becomes hard and does not have enough resiliency to yield slightly when first brought into frictional contact with a flywheel rim, this results in harsh engagement. To insure gradual clutch application the friction lining should be soft and elastic. If the leather has not been charred or is not worn too much it may often be softened by rubbing it with neatsfoot oil and allowing that substance to soak into the pores of the leather. Kerosene oil
is often enough to keep the clutch leather soft and pliable, and it has an added advantage in that it has so little lubricating value that the clutch members are not likely to slip because of reduced friction. Kerosene also has a quick penetration property that is valuable and does not collect grit or gum. Cylinder or machine oil should never be used to soften a clutch leather.
When a cone clutch slips and the friction facing is not worn or the spring tension is not lessened the trouble is usually due to a coating of lubricating oil on the frictional material, that reduces the friction so that the pressure of the clutch spring is not great enough to keep the clutch parts tightly pressed together in positive driving engagement. A simple remedy for this defective condition is to absorb the surplus lubricant by rubbing a small quantity of Fuller's earth into the leather surface. When a clutch cone is assembled it is not easy to reach the friction lining. The first step is to disengage or release the clutch and fasten the releasing mechanism in such a way that the clutch cone will stay out of engagement even when the pressure is released on the pedal. On some cars the clutch release and emergency brake applying mechanism are interlocked so that applying the hand lever will release the clutch. The clutch may be held out of engagement in this case by latching the emergency brake lever. The Fuller's earth is placed on a piece of paper or card so it can be sprinkled into the space left between the male and female members. Powdered borax is often recommended for the same purpose. Rosin is sometimes advised, but this material should not be placed between the clutch members, as if there is any tendency to slipping and any generation of heat it may be melted and will become a lubricant that will intensify the slipping instead of acting to absorb the oil, as the Fuller's earth or borax will.
If slipping is caused by a broken clutch spring, which is a very rare occurrence, or by weakening of the clutch spring, which is more common, the method of repair is evident, this consisting of substituting springs of proper strength where no adjustment is provided or by increasing the degree of compression of the weak spring if some method of compensation for shortening the spring is provided. Another annoying condition when a cone or three
plate clutch is used or where the clutch-driven members are of large diameter and have considerable weight, is "spinning" or continual rotation of the male clutch member when the spring pressure is released. This is often due to inertia, but is sometimes caused by a defect in the clutch mechanism. If the bearing on which the cone revolves when disengaged is not properly lubricated or if a poor grade of grease is used for this purpose the bearing may stick and the male clutch member will continue to rotate, even when the spring pressure is released. The ball thrust bearing employed to take clutch spring reaction, and which is clearly shown in the various sectional views previously described and in Fig. 318, which shows a cone clutch partially dismantled, may become wedged by a broken ball or particles of foreign matter, and if rotation of the parts relative to each other is prevented the rotation of the crankshaft will be imparted to the cone member through the clutch spring, which must turn with the crankshaft instead of remaining stationary, as would be the case if the ball thrust bearing were functioning as it should.
A seized clutch spindle bearing can only be repaired by taking the clutch apart and dressing down the scored journal, supplying a new bushing and removing the cause of the seizure. Sometimes when the clutch cone is carried on plain bearings wear in these members will permit the cone to sag because of its weight, and even though the spring pressure is fully released the lower portion of the cone will come in contact with the flywheel and the cone will be kept in rotation. Faulty clutch action is often traced to points distinct from the clutch mechanism itself. This applies to all types of clutches. Many cases of failure of clutch to release have been found due to imperfect relation of interlocking levers or rods or depreciation in some mechanical parts. If the clutch shifting collar is worn unduly or the small pins in the rod yokes connecting the clutch pedal with the release mechanism have worn, the pedal may be fully depressed and yet the pressure of the spring keeping the parts in contact may not be reduced to any extent. Where the emergency brake lever is interlocked with the clutch release leverage it may be possible that an adjustment of the brake rod, if these are shortened to compensate for wear of the brakes, will
change the length and may throw out the clutch mechanism slightly and cause slipping of the clutch because the spring pressure may be partially relieved.
The clutch release mechanism used on the Overland car as well as the provisions for adjusting the clutch spring are clearly shown at Fig. 319. When the clutch cone facing wears the only remedy is to dismantle the clutch, as shown at Fig. 318, which permits one to remove the old clutch lining from the cone and rivet a new one
Fig. 317.-Pattern for Cutting Clutch Leather for Overland Model 80
and 81 Cars.
in its place. If the old facing can be removed without breaking, it may be employed as a pattern or basis for a new lining. If the car is a model of standard make and recent manufacture the best plan is to obtain a new clutch facing from the manufacturer. However if the car is an old model or if the facing must be put on immediately it is not difficult to lay out a clutch leather that will go in place without difficulty.
The first step is to lay out the clutch to exact size on heavy