There are many possible causes for a transmission line vibration. Your wheels, tires, axles, driveshaft, transmission, clutch or torque converter, and engine components rotate at a high speed, and one or more of these components can create vibration if worn or out of specification. Worn or broken engine or transmission mounts can transmit normal vibrations that are usually never felt, and accidental body contact with the engine, transmission, or exhaust can also be misinterpreted as driveline vibration. transmission. The first step in diagnosing classic car vibration is determining exactly when and under what conditions the vibration occurs.
There are three basic types of vibrations:
1. Related to engine RPM – If vibration is related to engine RPM, it will occur in all gears (and possibly even stationary) at a particular engine RPM or higher. This vibration can generally be attributed to the motor itself or anything else that rotates at the same speed as the motor, such as the harmonic balancer, flywheel or flex plate, pilot bearing, pressure plate, torque converter, or the transmission input shaft. Body contact with the engine, transmission, or exhaust may also cause vibration related to engine RPM. Worn or broken engine or transmission mounts can contribute to this problem. When driving the vehicle with vibration present, maintain the vehicle speed and try to downshift or higher. If the vibration changes or disappears while maintaining the same vehicle speed, then the problem is not related to the engine RPM.
2. Related to vehicle speed – If the vibration is related to the speed of the vehicle, it will not be present until it reaches a certain speed, and then it will usually start gradually and then get worse as the speed increases. In some cases, it will slow down at some point and then come back at a higher speed. This type of vibration could be related to your wheels, tires, axles, differential, driveshaft runout, balance or angles, universal joints, or transmission output shaft. Take the same driving test as above. If the vibration is present in third gear at 50 mph, but shifting to fourth gear at 50 MPH makes the vibration go away, then it will not be related to vehicle speed and you can generally rule out any rotating components further back. than the transmission output shaft. At a given MPH, the output shaft, driveshaft, axles, wheels, and tires rotate at a constant speed, no matter what gear the transmission is in.
3. Related to acceleration / deceleration / cruising – A vibration that changes depending on whether you are accelerating, decelerating or cruising at a constant speed could have several different causes. Generally, this will be related to driveshaft angles or a worn or broken part, rather than something being out of balance. Think about what changes when the engine is under load. The loads on the motor and the bushing bracket change; the load on the pinion bearing changes; your driveshaft angles change, possibly more than they should due to a broken engine or transmission mount; your exhaust, shifter, transmission, etc. it could be in contact with the body only in acceleration or deceleration; If the car has been lowered (or raised), its suspension shock absorbers could prematurely be in contact with the body.
A vehicle works as a system and you must understand the relationships between the different parts when trying to diagnose a driveline vibration. Determining whether the vibration is related to engine speed, vehicle speed, or engine load will help you narrow down the list of possible culprits and prevent you from wasting time looking in the wrong places.