Backdrive or Interlock Linkage
I have a 1969 Corvette. Can someone explain the cable that runs from the transmission to the bracket on the steering column? The bracket is on the engine compartment side of the firewall. In my reference books it is called the "Backdrive" or "Interlock Linkage". I have not been able to find out exactly what the purpose of this cable is for.
-
-
Re: Backdrive or Interlock Linkage
It rotates the column to a "lock" position when you put the car in reverse (4speed) or park (auto). That allows the key lock cylinder to rotate to it's "lock" position where you can remove the key. Is yours connected and working? If not, your column has probably been placed in the "locked" position and secured in some manner. Otherwise, you couldn't remove your key. Chip. -
Re: Backdrive or Interlock Linkage
Thanks Paul for the info. This cable is missing from my car. I am able to move the key lock cylinder to the lock position and remove the key without any problems. My transmission is a four speed and the shifter has been switched to a Hurst. The attachment lever is still on the steering column but is not being used. Does this present any danger driving the car?Comment
-
In Appreciation of John HinckleyComment
-
Re: Backdrive or Interlock Linkage
1969 was the first year for the function locking steeirng column. General Motors was concerned that someone could turn their ignition key to OFF-LOCK while driving. This could lock the steering wheel while driving and could hold GM libel. So they came up with a cable or linkage system that connected to a lever on the lower end of the steering column.
As mentioned previously, your auto trans had to be in PARK and your manual trans had to be placed in REVERSE. The back drive system moved that lever to the full UP position (about 1 o'clock if you could actually see the lever from the driver seat). Moving the lever UP opens a gate in the steering column head and allows you turn the ignition key to OFF-LOCK. Note, with the cable or linkage system correctly engaged, you can always turn your engine OFF, but you cannot continue turning your ignition key to OFF-LOCK. So this system prevents you from locking your steering wheel when the car is capable of moving forward.
A lot of people have pinned or strapped the lower lever in the full UP position. It doesn't hurt any thing. But the steering wheel can be locked with the car moving straight ahead.
Here is a paper (complete with drawings) that provides all the explanation you will ever need on this subject.
Good luck,
JimLast edited by Jim S.; August 19, 2014, 07:02 AM.Comment
-
Re: Backdrive or Interlock Linkage
Hi Thomas,
This is the typical connection at the transmission reverse lever and at the interlock cable to the lever on the steering column
Perhaps they will help you determine what else besides the cable, if anything, is missing from your 69.
Regards,
Alan71 Coupe, 350/270, 4 speed
Mason Dixon Chapter
Chapter Top Flight October 2011Comment
-
Re: Backdrive or Interlock Linkage
Thanks to all who responded to this topic. All the information is greatly appreciated. After considering all the info it looks like the lever on the steering column may be retained in the non-locked position by the large spring that circles the steering column. When the transmission is placed in PARK (on automatic trans.) and REVERSE (on manual trans.) the interlock cable would push up on the lever placing it in the locked position. Since the cable on my car is missing I hope I can assume the large spring is holding the lever in the down position which is unlocked and my car would be safe to drive with the lever in this position. This raises this question.......If this lever is not in the UP position how am I able to turn my ignition switch all the way into the locked position and remove my key. Am I missing something or is it possible someone has changed something within my steering column. I have owned this car for 15 years and am just now finding out that this interlock cable is missing. My main concern is that my car is safe to drive without the steering column locking up on me.Comment
-
Re: Backdrive or Interlock Linkage
The spring in the following pictures does not prevent the lever and shift tube from rotating.
You will want to use a small set screw or wire the lever in the UP position.
If the lever moves out of the UP position, there is not a particular safety concern. However, you will find that you cannot rotate your ignition key to the OFF-LOCK position so that you can remove your ignition key.
A point of information: There are five positions for a C3 ignition switch mounted on the steering column. From full clockwise to full counterclockwise; START, RUN, OFF, OFF-LOCK, and ACCESSORY.
JimComment
-
Re: Backdrive or Interlock Linkage
Thomas, either it is in the locked position now or something has been disabled within the column. I can't remember whether up or down is locked. My car is in pieces (as all my toys are) and I will have to look for a column tomorrow to confirm. The ability to turn your lock cylinder to the LOCK position and remove the key with the car in gear and presumably under way is the unsafe situation the interlock would prevent. As long as you make certain you don't cut off the ignition while driving, you will be fine. If you fear it could happen, you may want to repair it. Look under the car at the driver's side of the trans and see if you have a bracket there to mount the cable to. The reverse lever will need to have an extension on it for the cable to attach to. My car has a Hurst shifter in it also and it has a lever that the cable connects to. You may just need a cable and some clips. The AIM will show you all the parts. Back up light switch mounts in that area also. Could be a fun project sorting out that area. Chip.Comment
Comment