20. What is the minimum number of U-joints that would have to be used in the drive shaft assembly of a tandem drive axle truck equipped with a hanger bearing on the front drive shaft?

To determine the minimum number of U-joints required in the drive shaft assembly of a tandem drive axle truck with a hanger bearing on the front drive shaft, we need to consider the configuration of the drive shaft and the function of U-joints. 1. **Understanding the Drive Shaft Configuration:** - A tandem drive axle truck typically has two drive axles. - The drive shaft connects the transmission to the rear axle and may have a hanger bearing to support it. 2. **U-Joint Functionality:** - U-joints (universal joints) are used to allow for the transmission of torque while accommodating angular misalignment between the drive shaft and the axles. - Each segment of the drive shaft that changes direction or has a support bearing typically requires a U-joint. 3. **Analyzing the Setup:** - In a typical setup with a front drive shaft leading to a hanger bearing and then to the rear axle, we can break it down as follows: - The front drive shaft from the transmission to the hanger bearing will require one U-joint. - The rear drive shaft from the hanger bearing to the rear axle will require another U-joint. 4. **Conclusion:** - Therefore, for a tandem drive axle truck with a hanger bearing on the front drive shaft, the minimum number of U-joints required would be **2**. Thus, the answer is **2 U-joints**.