in figure 11-2. Consequently, it is not possible to discuss all makes and models that you may encounter in the Navy. The information contained in this section is general; for problems and procedures on any particular transmission, consult the manufacturer's manual.

It is seldom that the transmission of a vehicle is manufactured by the same company that manufactured the vehicle. Some manufacturer who specialized in building automotive parts generally makes the transmission and sells it to the vehicle manager. A nameplate attached to the side of the transmission case will have the manufacturer's name and the model number of the transmission. The Spicer Company, for instance, uses a four digit number for a model number, such as 8051. The third digit of the number indicates the number of forward speeds available in that particular transmission. Therefore, the model 8051 is a five-speed transmission.

If a transmission does not have a nameplate, refer to the vehicle manufacturer's manual for identification.

TROUBLESHOOTING TRANSMISSIONS

It is important that transmissions troubleshooting be done by trained, experienced mechanics. Many times an operator will report transmission noise on the Operator's Trouble Report, when, in fact, the noise maybe coming from some other component of the power train of the vehicle.

Noises that appear to come from the transmission but actually originate at some other point are many and varied; for example, unbalanced propeller shaft, defective wheel bearings, or damaged tires on a vehicle may cause noises that are transmitted to the transmis- sion. These noises have no particular or characteristic sounds that would indicate their origin; therefore, they are difficult to identify.

Torsional vibration is one of the most frequent causes of noises that appears to be in the transmission, but actually originates outside of it. Included among these possible outside torsional vibrations are the following:

1. Propeller shaft (drive shaft) out of balance

2. Worn universal joints

3. Drive shaft center bearings loose

4. Worn and pitted teeth on axle pinion and ring gear

5. Wheels out of balance

Figure 11-2. - Typical example of a heavy-duty truck transmission.