Fig. 36. Tooth Contact Impressions

Fig. 37. Installing Bushing In Rear Half of Diff Case

TM-5-3820-256-24-5 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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SERVICE MANUAL Check Gear Tooth Contact The final check of differential assembly adjustment is checking the gear tooth contact by the paint impression method. Apply oiled red lead lightly to the hypoid gear teeth. When the pinion is rotated, the red lead is squeezed away by the contact of the teeth, leaving bare areas the exact size, shape and location of the contacts (Fig. 36). Sharper impressions may be obtained by applying a small amount of resistance to the gear with a flat steel bar and using a wrench to rotate the pinion. When making adjustments, check the drive side of the gear teeth. Coast side should be correct when drive side is correct. Generally, coating approximately twelve teeth is sufficient for checking purposes. With adjustments properly made, a correct tooth contact similar to that shown in Fig. 36 will be secured. The area of contact starts near the toe of the gear and extends about 62 1/2 percent of the tooth length. This adjustment results in a quiet running gear and pinion set which, because the load is distributed over the teeth within the proper area, will deliver all the long service built into it. When checking paint impressions on gear teeth of an axle under heavy load, the impressions usually spread out somewhat longer than the patterns obtained from a bench test. This can be considered as normal. Ring gears when mounted should show a bearing toward the toe or small end of the tooth, but never at the heel or large end. The reason being that it is practically impossible to make gears and gear mounting so rigid that no deflection will occur when full torque is applied. This deflection causes the bearing to approach the heel of the tooth. And when gears are adjusted so that the bearing is toward the heel of the tooth, it results in a concentration of load on the top corner of the heel and breakage will follow. Fig. 36. Tooth Contact Impressions 1 Drive 2 Coast 3 Cross Bearing 4 Bearing Too High 5 Bearing Too Low 6 Too Much Heel Bearing 7 Too Much Toe Bearing 8 Proper Tooth Contact CTS-4044 PRINTED IN UNITED STATES OF AMERICA Page 20

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