KitchenAid mixer grinding noise: what it means and what to do

What the worm gear does

Inside the head, a worm gear passes the motor's spin down to the gears that turn the beater. It is the sacrificial part, on purpose: it is meant to wear out or strip before the motor and the harder parts take the damage.

When its teeth strip, the motor keeps running but the beater turns slowly, stutters or stops. That is the classic sign.

Signs of a worn worm gear

• A grinding or whining noise that is new, or getting louder
• The motor runs but the beater stops or stutters, especially with dough (see beater not turning)
• Bits of plastic or metal shavings in the old grease
• An oil leak or dark grease showing at the same time (see leaking oil)

Other causes of a noisy mixer

Old grease that has dried out or broken down stops protecting the gears, and heavy dough loads and heat wear them faster. Kneading above speed 2 is the most common way a worm gear gets stripped. On an older machine other gears can wear as well. Some noise is normal, because these mixers are not quiet, so the key question is whether the sound has changed.

What to do

1. Stop using the mixer and unplug it. Running it on can cause more damage.
2. Do not mix anything heavy while you decide.
3. Have it looked at. It is a repair many handy people do at home, but it means opening the gearcase, cleaning out the old grease and refilling it correctly.

My full tune-up is the repair for this: a new worm gear and gasket, the old grease cleaned out, the mixer repacked with fresh food-grade grease and test run under load. If you are not sure what is wrong, the diagnostic finds the actual fault, and its price comes off the repair if you go ahead.

Older mixers can grind too

Older machines such as the K45SS and K5SS can develop the same problem, and they are usually worth repairing. If you are not sure how old yours is, the serial number decoder will tell you when it was built.