REWORKING A STEERING COLUMN FOR A DISABLED SHIFTER INTERLOCK
For many post-1969 GM muscle cars with headers, it’s necessary to remove the steering interlock (also called the back drive) to allow for clearance. The back drive was a major part of the antitheft steering column system introduced in all 1969 GM passenger cars. With the back drive, the car had to be in Park (automatic transmissions) or Reverse (manual) to get the column to lock and allow you to remove the key. The lockout mechanism on manual transmissions also performed the backup light activation at the same time by rotating the column sleeve that the switch was hooked to. It’s possible (with lots of effort) to modify a back drive to work, but it all depends upon the application and the headers in question. In order to get the backup lights working, Hurst Shifters offers a bolt-in switch kit (PN 2480003).
Removing the back drive and installing the switch is easy enough, but then you have another issue to deal with. You have to stop the column from rotating. We came up with a clean fix that’s illustrated in the photos. As a result, the key was easy to remove, and as a bonus, something like a column-mounted tach remains in one spot.
One of the best parts of the fix is the fact that a column-mounted tach can’t flop around with the back drive disconnected. Plus, it allows you to remove the key easily.
In order to stop the steering column interlock from rotating (with the back drive removed), we cut away most of the mechanism linkage on the engine compartment side of the column (our car was originally a column shift example) and left just enough to mount a safety-drilled AN bolt/ locknut combination (the bolt is drilled on the threaded end).
The mod is very unobtrusive. At first glance in this empty engine compartment it’s difficult to spot.
To find a spot to anchor the mechanism, we simply drilled a small hole into the column and fished in a section of safety wire.