Why GM car keys went in with the teeth down
by Richard Henley
In the grand old days before we, and probably our fathers, were born, Chrysler locks were built by Yale and Ford locks were built by Hurd. These were the common design called “pin tumbler”locks; they were pretty much identical to the locks on houses.
Without getting into too much technical detail, these locks work best with gravity helping the tumbler springs to seat the pins, and the same gravity keeps dust and water out of the pin holes; so the design uses the key in the “tooth up” orientation.
In those same grand old days GM locks were built by Briggs & Stratton (yes, the same people that build lawnmower engines), using a design technically called “flat tumbler side locking bar.” Ultimately, this is a more secure locking system, virtually pick-proof, but does have some other limitations. These locks work well in virtually any position, but key and component wear is decreased with the key in the “tooth down” orientation.
There is another type of lock called “wafer tumbler,” but in American cars up to the late 1980s, these were pretty much restricted to glove box locks. These locks work well in about any position, but aren't as secure as the others by design. It wasn't until double sided keys were the norm that acceptable levels of security became common with these locks; making the tumblers work on both sides of the key and having twice as many tumblers made them harder to manipulate without the key.
The modern design of these locks was pioneered by the foreign automakers in the 1970s, and some of the high end European marques have furthered that technology with designs that work on 4 sides of the key and have over 20 tumblers, in some cases combining it with a sidebar much like the old GM locks. Security was enhanced with electronic chips, a technology pioneered by GM with the VATS system in the 1980s.
My brother is still in the locksmith trade, but I left it in the mid 90s. One of the reasons I left was that locks were getting what I termed “locksmith proof” by then. In some cases a simple lock failure that in the days of old a service truck could be sent out and have the car fixed in an hour or two was being transformed by new technology into a situation requiring the car to be towed to the shop and a day or two of time to fix, some of which was waiting for the manufacturer to ship parts not available at the dealership. Last I spent a bit of time visiting with my brother at his work I was amazed that some of the cutting edge technology that I had to deal with then is now as obsolete as the mini pin tumbler Hurd locks on Fords from the 1950s was when I was a locksmith.
By the way, one of the common house calls when I was a locksmith was repairing house locks for people who had installed their own — GM car owners who had installed the house locks in the tooth down orientation, resulting in frozen tumblers and a key that wouldn't work.