1.Torque converter slippage
(1)Noise caused by imbalance
If there is an imbalance in the pump impeller, and another behind the turbine runner, such as in the propeller shaft, each one of these components will produce a vibration.
Because the torque converter by nature has slippage, the relative imbalance between the pump impeller and the propeller shaft will appear to rotate gradually around their common axis.
When the imbalance of the pump impeller is on the opposite side in relation to the imbalance of the propeller shaft, vibrations will be smaller than when the imbalances are both on the same side.
These two varying vibrations are transmitted to the body panels through the engine rear support members or suspension arms bushings to produce the beating noise.
(2)Noise caused by torque fluctuations
2.Vibrations due to transmission gear ratio
Besides the body beating noise created by torque converter slippage, the transmission gear ratio – such as overdrive in an automatic transmission, or 5th gear in manual -sometimes causes the engine vibration frequency to approach the drive train vibration frequency, resulting in body beating noise.
3.Vibrations due to pulley ratio
If the diameter of an accessory pulley and that of the crankshaft are close to integer multiples (e.g., 2 or 4) of each other, the differences in the vibration frequency of the engine and that of the accessory become small, and combine to produce body beating noises. When this is the case, pinpoint the source by removing the drive belts one at a time. This will enable you to isolate the problem pulley.
4.Vibrations due to differential reduction ratio
1.To determine whether a beating noise is caused by torque converter slippage or not, you only need to vary the pressure of your foot on the accelerator pedal. If this alters the frequency of the noise, you have isolated the source of the symptom.
2.A four-cylinder engine is more prone to body beating noise created by torque converter slippage when the joint angle of the propeller shaft is great.
3.Since body beating noises are created by the combination of two different vibrations, they can be eliminated by either increasing the difference between these two frequencies, or by reducing the vibration of either one.
4.When test driving for these body beating noises, do not accelerate or decelerate abruptly; if you do this, you will exceed the vehicle or engine speed at which the symptom may be duplicated.