Caviar Gloss KitchenAid Professional 600 Series 6-Quart Stand Mixer KP26M1XCV

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I recently purchased the Kitchenaid Professional 600 and so far it has been a wonderful addition to our kitchen. Many people have written both positive and negative reviews of this model, and that concerned me - especially since this was a gift for my wife and I didn't want it to be plagued with problems. For anyone who is considering purchasing this model (and for many who already have), you probably already know about the issue with the gearbox cover that was originally made of plastic instead of metal. Supposedly, the cover would overheat and crack, causing the gears to strip. This issue existed several years ago and due to the number of complaints, Kitchenaid has since returned to an all-metal gearbox cover.

However, after a great deal of research I have been pretty well convinced by a very educated poster on another forum that the problem did not originate with the plastic cover. This person went to great effort to disassemble his broken mixer and document what had happened and what he found (with some very interesting pictures) as he fixed his Pro 600's gearbox.

Specifically, there was one set of gears on a vertical shaft that wanted to rise upwards when placed under a load - a common phenomenon with gears due to the angle of the sides of each tooth. As he documented, there was a clip missing from the shaft directly over the gearset, and that allowed the gears to ride up the shaft and put pressure on the plastic cover from the inside. Over time, the plastic (which was never intended to be placed under pressure from underneath) cracked and the gears lost contact with each other and stripped.

I now have come to believe that a great many people who have this older design (plastic gearbox cover) and have never had a problem do have this clip properly in place, and the clip is either missing or broken for those with this design who have had issues with their gears. This is the only way to reconcile why only some people with the plastic cover have problems while many others do not.

It seems that the newer design (metal gearbox cover) now has the ability to withstand the pressure of the gears if the clip is missing, which while not a desirable way of designing the cover it does provide a certain degree of "back-up" if the clip that holds the gears down onto the shaft is missing or goes astray.

If you were one of the many people who complained to Kitchenaid about this problem, they may have been absolutely correct if you were told that the cover was truly not the issue. However, they do get a failing grade for not understanding that it was most likely this missing clip on the shaft that was the originating cause and the cracked cover and stripped gears were only a symptom (albeit fatal) of the true problem.

It also appears from some basic research that Kitchenaid has fully adopted the all-metal gearbox cover since around the first quarter of 2007, so unless the mixer you are just now purchasing is very old stock you should have no problems with the gears in you Pro 600. I have taken the time to check our mixer (which was originally purchased on November, 2008) and the cover is metal and the clip is in place. On the flip side, if you are one of the posters who are just now getting around to writing a negative review about your 2-3 year old Pro 600 with gear and plastic cover problems then you might want to have this checked out.