In this, article we look at common problems that cause a clunk or thud noise when taking foot off the accelerator pedal. 

Symptoms

  • Car thuds when letting off-gas
  • Noise when taking the foot off the accelerator
  • Clunk noise when letting off the gas pedal
  • Knock sound when letting off-gas

Common Causes

Worn mounts, suspension and steering problems can all cause a knocking noise when taking the foot off the accelerator pedal.

Let's take a look at some of the most common problems.

Differential Mount

mercedes thump clunk when letting go of gas pedal

These symptoms were caused by a bad front differential bushing. The bushing shown in the picture will crack and create too much free play for the differential. To verify jack up the car. Grab the end of the front differential (carrier) and check for play.

If there is any play or cracks, the rubber bushings should be replaced.

Also visually inspect the rest of the front differential bushings for cracks. There are three bushings. mercedes front differential bushings

The rearmost bushing seems to fail most often.

Engine or Transmission Mount

Bad engine mount

Another common issue that causes similar symptoms is a broken engine or transmission mount.

Control Arm Bushing

Control arm bushing

A worn control arm or thrust link bushing can cause a hit when accelerating or braking. It can be an indication of an extremely worn bushing. 

Do not ignore a car that thuds when taking the foot off the accelerator pedal. Your vehicle may have a serious issue that needs to be repaired immediately or risk putting yourself and your passenger at risk.

Have an auto mechanic perform a vehicle inspection to determine why your car makes a knocking sound when letting off the gas pedal.