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not silence the noisy action, the gears should be inspected to see that the teeth are not worn too much and that they are meshed properly. If there is too much play between the gears, there is apt to be a rattle or knocking in the rear axle instead of a grinding noise. If considerable looseness exists between the gear teeth, an effort should be made to eliminate practically all lost motion by moving the entire differential assembly nearer to the bevel pinion which can be easily done in most forms of floating axle or by meshing the pinion more deeply in the ring gear.

Q. Does differential gearing ever give trouble, and how is it evidenced?

A. The differential gearing of most cars is so strongly made and so simple in construction that it is not apt to cause trouble. Differentials of the bevel pinion type which have stronger teeth are not so apt to become broken as are those of the spur pinion type. If the differential is not functioning properly there will not only be difficulties in steering but there may actually be a failure in the final drive. The most common differential gear trouble is stripped pinion teeth. Sometimes, in cases where a differential has been used for some time, the gear teeth may become sufficiently worn so they will break off. The only remedy for this defective condition is to remove the entire differential assembly from the rear axle and substitute new gears. A differential is apt to be noisy in action if the pins on which the gears revolve become worn. If the driving keys or pins by which the live axle shafts attached to the wheels are driven become loose they are apt to shear off and failure of drive is inevitable.

LESSON THIRTY-FOUR

CHASSIS TROUBLES AND ELIMINATION

Q. What can be done if frame side member sags after it has been in service for a time?

A. The weakened frame member may be re-enforced by means of an internal steel plate that fits in the channel and which extends as far as possible on each side of the weak point or the frame may be brought back in place and kept in line by means of a simple turnbuckle truss rod which extends from one end of the frame member to the other.

Q. Why must frame members be straight?

A. If the frame members sag and the transmission and power plant are separate units, these members will get out of line and considerable binding of the clutch or gearset bearings may result.

Q. What happens if frame rivets are loose?

A. If the rivets by which the various gusset plates and cross members are secured to the frame side members become loose the frame structure is seriously weakened. If the rivets have become worn and the holes enlarged it will be necessary to replace them with larger rivets which must be forced tightly in the enlarged hole and then securely hot riveted in place. A frame having loose rivets is apt to squeak and will not maintain the proper alignment between the engine and the gearset.

Q. What attention do springs need?

A. Springs require very little attention, the main points being to keep the spring clips tight and to keep the spring shackle bolts oiled. The springs should not be allowed to get rusty because their smooth action will be impeded if rust accumulates between the laminæ or leaves of which the spring is composed.

Q. What is a sure indication of rusty springs, and how can it be prevented?

A. If springs are rusty, either at the spring shackles or between the leaves, a squeaking sound will be heard whenever the car is operated over roads requiring much spring action. This squeaking may be easily prevented by separating the leaves of the spring and inserting oil or graphite grease between them.

Steel Bar Ortire Iron

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Fig. 296.—Methods of Making Emergency Spring Repairs Outlined. Q. What causes spring breakage?

A. If a car is driven at high speed over very rough roads or if it is loaded beyond its capacity, the springs are apt to be deflected beyond the safe point and will break on the rebound, especially if the wheels strike an obstruction or drop into a hole in the road when revolving at high speeds.

Q. Describe emergency road repair in event of spring breaking.

A. If a spring breaks at the center where the bolt goes through as shown at A, Fig. 296, it may be repaired temporarily by placing a rubber bumper or block of wood over the break and putting a steel bar or heavy tire iron over it and firmly attaching to each end of the spring by leather belt lace, rope, or wire. If the break is at a point between the center and one of the spring eyes, the spring may be repaired as outlined at B, Fig. 296. In this case the block of wood is placed over the fracture and the iron bar fastened to the spring, as indicated.

A useful accessory that may be carried in the tool box, as it occupies very little space, is outlined at Fig. 297. This spring repair member is a steel forging or casting, provided with a pair of repair clamps so it may be firmly secured to the spring member. This is

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Fig. 297.—How the Emergency Spring Repair Member is Utilized

When a Spring Breaks at the Center. a much better temporary repair than those shown at Fig. 296 and the repair member is equally useful if the break is at the center or if it is near the end. One advantage of the construction is that it may be used to replace one of the spring eyes, should that member break off. If a spring breaks and no material is at hand for repairing it the spring may be relieved of the car weight by filling the space between the car frame and the axle with a heavy block of wood and tying this securely in place to prevent it from falling out. A car may be driven several hundred miles at moderate speed when repaired in this manner even if a spring is broken beyond repair.

Q. What is the main cause of back lash in steering gear?
A. The main cause of lost motion in the steering gear is depre-

ciation of the reduction gears and wear at the various joints on the drag link or tie-bar.

Q. How is lost motion in gears taken up?

A. A typical steering gear assembly and front axle parts are outlined at Fig. 298. Lost motion between the gears when of the form shown may be eliminated by removing the steering arm from the worm gear and turning that member around in its bearings so that new teeth come in contact with those of the worm on the steering pillar and then replacing the steering arm. The wear usually occurs at that point of bearing between the teeth in contact when the hand wheel is set in the straight ahead position because the irreversible worm gears used do not permit the steering post to turn when the wheels strike an obstruction and therefore all the shock is taken on the teeth of the gears.

If the bearings supporting the worm gear to which the steering arm is attached are worn, they may be replaced with new members so there is no lost motion at the bearing. If the steering post has an up and down movement, this may be prevented by screwing down the adjusting nut at the top of the gear casing, which will bring the thrust bearing parts in closer relation. If the ball thrust bearings are worn unduly, these members should be replaced. The hand wheel should be firm on the steering post as sometimes the key by which it is fastened may wear to such an extent that the wheel spider will be loose on the steering column even if the reduction gears are tight. Another point that demands inspection is the anchorage of the wheel rim on the spokes. Lost motion at the other points in the steering system will also tend to produce back lash at the handwheel.

Q. What causes stiff action of steering gear?

A. If the joints on the tie-bar and drag link become dry and the bearings of the worm wheel shaft and steering post are not properly lubricated the action of the gearing is apt to be stiff. Some forms of steering gears may be adjusted by eccentric bushings which may be oscillated to bring the worm and worm gear in closer relation. If the bearings are turned so that all lost motion is eliminated with the gearing in the straight ahead position, the action

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