Reverse lock out mechanism (back drive linkage)

Allison Winn

Veteran Member
Jan 10, 2021
436
Ok I am going batty trying to get my reverse lights operational. I'm SURE I am not the first to go crazy, it seems so simple...
Car is a 70 4 spd. It has correct trans and shift levers and shifter. All back drive parts are repop but I compare them to this Manual pic below and they appear pretty close.

Here is my dilemma - my car matches the comic strip drawing. But the geometry is all wrong. In the pic the trans in in neutral. Shifting to reverse moves the reverse lever to the REAR so it PULLS on the rotating bellcrank. PULLING on the bellcrank PUSHES the rod that goes up to the column. But all the way up is PARK - this rod needs to move down to get the reverse lights to come on, not up.
Screenshot_20220918-224723_Chrome.jpg
 

72SS9681

Member
Jul 20, 2014
98
Walla Walla, WA
GM set up the linkage so that the column is in the lock position (rotated counterclockwise) when the transmission is in reverse. So when you move the transmission to neutral it pulls the lever down turning off the reverse lights. When you adjust the linkage you'll need to put the transmission in reverse then adjust the rod so that your column is in the locked position. Once you have the linkage adjusted you'll need to adjust the reverse light switch at the bottom of the column so your reverse lights work correctly.
I was trained to put a manual transmission car in 1st when securing the vehicle so I struggled with this also.
Pictures are of my 72, car is in neutral. I replaced the muncie shifter with a hurst but they work the same.
 

Attachments

  • 72 93.JPG
    72 93.JPG
    215.8 KB · Views: 33
  • 72 96.JPG
    72 96.JPG
    232.3 KB · Views: 34

fbody_mike

Veteran Member
Mar 24, 2009
1,036
San Gabriel Valley, California
Was your column originally for an automatic car? The manual cars got a different switch for reverse. But I think you can make an auto one work if you get enough adjustment out of it.

Keep in mind that the reverse lockout was mainly a safety feature as it prevents you from turning the key all the way off while the car is moving forward. If you can not turn the key all the way off you can't lock the steering wheel.
 

Allison Winn

Veteran Member
Jan 10, 2021
436
Might be the problem - car was originally automatic. I moved the green and pink wires from the shifter to the column switch - either I put them in the wrong place or the switch is indeed different. That would explain everything - if indeed the lights are supposed to be on when the lower column lever is in the full "up" position coinciding with the key release mechanism. I'll check tonight
 

Allison Winn

Veteran Member
Jan 10, 2021
436
So I pulled the switch out to take a look. This is it - and I had the green and pink connected to the middle in line pair. Nothing was connected to the other 4 terminals. Looks like I can put the wires to the left most pair and all should work?
20220920_202723.jpg
 

Green hornet

Veteran Member
Oct 11, 2015
2,100
North Bay, CA
Might be the problem - car was originally automatic. I moved the green and pink wires from the shifter to the column switch - either I put them in the wrong place or the switch is indeed different. That would explain everything - if indeed the lights are supposed to be on when the lower column lever is in the full "up" position coinciding with the key release mechanism. I'll check tonight
I converted mine from an auto to a 4speed. if I remember I used the switch from the auto shifter and had to put the wires on different terminals to make it work. The switch has some adjustment to fine tune it also. Here’s a photo of my switch if it helps any.

B8CBF0A9-6AEC-48B4-9BF5-B28400E1ECF6.jpeg
 

70RamAirIII

Pontiac-aholic
Jan 10, 2005
139
Calgary, Alberta
@ Allison
That is an automatic reverse light switch.
The manual one looks different (it's smaller and only has two plugs for the purple wire iirc).

The other variable that some people forget is the bellcrank(?; if that's what it's called);
This goes in between the column and reverse rod, and I believe that there are at least three different ones.
After that, it's all about the rods, and levers on the transmission.

I hope this helps!
 

72SS9681

Member
Jul 20, 2014
98
Walla Walla, WA
Sorry, didn't think about the switch. You had it wired correctly but the switch is different. The manual switch turns on the reverse lights when the column is rotated to the counterclockwise position the automatic switch turns them on when the column is rotated slightly to the right. The other lugs on the automatic switch are for the neutral safety so the car can only be started in the park or neutral position. Attached picture show the switches positioned with the reverse lights on, manual switch is on the left.
 

Attachments

  • 20220920_182614.jpg
    20220920_182614.jpg
    170 KB · Views: 33
  • 20220920_182745.jpg
    20220920_182745.jpg
    150.2 KB · Views: 32

fbody_mike

Veteran Member
Mar 24, 2009
1,036
San Gabriel Valley, California
When I converted mine to manual trans I purchased the manual switch. But there was a time in the past when I was trying to adjust the neutral safety on an auto car and got the adjustment bad enough that the reverse lights were on when the car was in park. So some switches must have enough slot in the screw holes to get it over far enough.

I also installed a clutch switch that connects to the purple wires, neutral safety for manual transmissions. Because sometimes I get tired and do dumb things, and accidently starting it in reverse while I am reaching in through the window will not be one of them. It was something I could see happening if the shifter is locked into reverse whenever the key is off.
 

Allison Winn

Veteran Member
Jan 10, 2021
436
10-4 and thanks all. It took every bit of my fab skills to work it out but she is all hooked up and works great. I too park my cars in neutral with parking brake on, so I can reach in to bump it over - not anymore.
FYI I used the reproduction kit and it sucks. The lower rod is 2" too long, had to cut and reweld it. Upper rod has the 1 bend clocked 90 degrees off.
I can see why so many got tossed - reverse light on when you turn the key, can't shut off unless it is in reverse - it isn't a smart set up
 




Top