Clunking noise when shifting from Drive to Park not always a cause for concern

The automatic transmission in my car occasionally makes a “clunk” noise when I shift from D to P. What are the possible causes and what can I do to avoid it? It feels like I am causing damage.

There are a few circumstances that can cause this. First, it may be the car rolling back a little when the lever is shifted to P before the parking brake is engaged.

The movement is due to the slight free-play in the parking-lock mechanism. Basically, a lever in the transmission, known as the pawl, slides into a slot on the toothed “parking gear”.

As the pawl is not a tight fit in the slot, the free-play allows some rotation of the gear and hence the car can roll a little forward or backward before the transmission is locked.

Under these conditions, there is likely to be a noise when you shift the lever out of P as the lock is released. This is not abnormal and nothing to be concerned about.

However, if this is a frequent practice, you could damage the parking gear or, in extreme cases, shear off the pawl. Therefore, always engage the parking brake before shifting to P.

The noise and additional movement can also occur when driving. Called shift-shock, this is most commonly due to higher-than-normal engine revving speed, which is bound to happen during a cold start.

Such shift-shock is not abnormal, but if you feel that it has worsened noticeably over time, you must have the transmission checked.

Usually, flushing and renewing the transmission fluid with the manufacturer’s recommended type and grade will alleviate cold-start shift-shock, but do also check that the engine and transmission mountings are in good condition.

A broken mounting can cause varying degrees of shift-shock, which will be particularly severe while shifting from P to D and shifting up gears during quick acceleration.