Final answer:
Technician A is incorrect as permissible u-joint working angles should not increase with driveshaft speeds to avoid vibration and damage. technician B is correct stating that driveshaft speeds can exceed 3000 rpm when a diesel engine truck runs at rated speed with the transmission in overdrive. this does depend on specific vehicle conditions and transmission technology.
Step-by-step explanation:
When discussing the relationship between driveshaft speeds and permissible universal joint (u-joint) working angles, Technician A states that as driveshafts speeds increase, permissible u-joint working angles also increase. this is incorrect. Actually, as driveshaft speeds increase, it is crucial to maintain minimal u-joint angles to prevent excessive vibration and potential damage. Thus, Technician A is not correct.
On the other hand, Technician B claims that when a truck diesel engine is run at a rated speed and the transmission is in overdrive, driveshaft speeds can exceed 3000 rpm. This statement is likely correct as overdrive gearing allows the engine to run at a lower RPM while the driveshaft turns faster, exceeding the engine RPM. Whether the actual speed exceeds 3000 rpm depends on the specific transmission ratios and vehicle operation conditions. It's important to note that modern transmission technologies such as 7+ speeds, dual clutch transmissions (DCTs), and continuously variable transmissions (CVTs) exist to improve fuel economy and reduce CO₂ emissions by optimizing the engine's operating range and efficiency.