Automatic Door Lock Replacement

We made a list of all the subsystems on our old Mustang. It's pretty long. What does this mean? More subthings to break. It's Murphy's Law of Coincidental Failure. Parts will degrade and at the most inconvenient moment they'll break. The trick is to stay ahead of what we call the "inclined degradation and breakage curve."

How They Work
Consider your automatic door locks. They're driven by an electric motor hidden within the rearward lower corner of the car door (note: access is a royal pain) and linked to the door lock mechanism by a length of forged helical rod steel. That motor is isolated by two rubber grommets, suspended in a plastic bracket. When the motor turns one way (hit the unlock button), it winds in the length of steel and pulls the locking lever down, disengaging the lock and raising the manual lock button. The opposite selection on the automatic lock button reverses the motor, extends the rod, engages the lock and lowers the thingy.


When this motor fails, it's usually because age causes the threads on the shaft to wear off; thus, the motor can't raise and lower said shaft—it grinds and buzzes instead. You'd best replace both locks even if just one breaks because logic suggests the other one is close behind (get ahead of the breakage curve). Figure the extra amperage available to the second motor when the first isn't working gives #2 the extra oomph to make chunks of its threaded shaft.

The Joy
Frankly, working inside the doors of any car built in the U.S. from '60-something to '90-something is about as pleasurable as setting a compound fracture in your kitchen. Difficult access, loads of rough metal panels rarely factory-de-burred and about as sensibly arranged as VCR instructions in a foreign language. Problem is, the mechanisms within have been installed once and that's it—meant never to be removed or repaired. This is in line with the prevailing, "A car should last 100,000 miles" design theory that pervaded much of the products turned out by the Big Three during the high-V, low-Q Halcyon days beginning roughly with Vietnam, lasting through the end of the Cold War. Currently, a much more level automotive playing universe has brought to bear revised standards for functionality and longevity, but that doesn't make replacing the door-lock motors in our Fox-body Mustang any less of a pain.

Shade-tree Shady
This is one of those little things you think you can ignore, the automatic door locks, so at first when they fail you just manually unlock the door and have a nice day. Cars age, right? Funny thing about even the simplest technology, it'll sneak up on you—and suddenly the driver's side door-lock actuator freezes up, shorts out the circuit and you're left to climb into your through the hatch, so you can let your date into the car. Golden moment there. So swallow your wallet just a little and pick up some new actuators and a box of Band-Aids.