During reassembly of my 1974 Carrera 2.7, I found that the left-hand door handle and lock had broken in a couple of places. One point of failure was in a lug that holds the door-opening mechanism in place on the inside of the handle, and the other was at the end of the lock barrel where it mated to the locking lever. I required a replacement handle but one with a fully functioning lock barrel. I duly sourced a good-condition handle, but of course my car key wasn’t the right one for the lock, so I set about replacing the components in the new lock barrel with the ones from my original.
The lock barrel contains 10 sliding metal plates, which with the key removed protrude from the lock barrel under spring pressure and prevent it from rotating. Each metal plate has a unique slot that moves the plate into the barrel against the spring when the key is inserted. The correct key will move all 10 plates exactly level with the lock barrel, allowing it to turn and lock or unlock the door. I started first by removing both lock barrels from their handles and then removing the 10 sliding plates from the replacement one, taking care not to lose any of the small springs which return them to the lock position. This barrel was then carefully cleaned and greased before removing each plate at a time from my original lock and replacing them in their respective position in the new one. During this process, I found that one of the small springs had failed, so I removed it with a very small screwdriver and replaced it with one from the original lock. Using my key in the lock, the lock barrel was refitted to the replacement handle and the locking lever and return spring refitted. In fact, the handle I’d bought was from a right-hand door, but the only difference is the locking lever, which I used from my original.