Author Topic: Backdrive Linkage: How the steering column is linked to console shifter  (Read 747 times)

firebirdparts

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This is recreated from a sticky thread we had.

Quote
Here's something that has always puzzled me.  On my '79 Trans Am there is a collar around the steering column that moves in conjunction with the console-mounted (automatic) transmission shifter.  If the car is in neutral, I can actually rotate this collar with my hands, which will move the console shifter and drop the car into gear.  I'm thinking this is dates back to when a column shifter was actually an option, but why in late model Firebirds and Trans Ams in particular was the collar still connected to the shifter after the column shift option went away?  Anybody know the history on this design?

Its called a backdrive mechanism....It controls the steering wheel lock, the neutral start switch, and the backup lights, all of which are mounted in or on the steering column.  the idea is that:
you cannot switch the key to the off position and remove it from the ignition (thereby locking the steering) unless the car is in PARK.  You cannot lock the steering wheel unless the car is in Park (and therefore not in motion).  Once the steering wheel is locked, the transmission is locked in park.  This was an anti-theft feature mandated by the US government in 1969.
For a manual car, the gearbox has to be in reverse to lock the steering wheel and pull out the key.

These parts can get lost, and they can interfere with headers, so sometimes we get questions here about how to live with this system 50 years later.

If you look under there, you'll see linkage rods going from the transmission to a shift arm on the bottom of the steering column. The linkage looks like the photo below. When you shift the floor shift, the linkage moves the arm which moves the collar on the column. This movement inside the column makes it so you can only turn the key and start the car in park and neutral, and also operates the back-up light switch that's attached to your column under the dash. And you can only turn the key to the lock position and remove the key when the shifter is in park.

Here is a diagram pictures of the automatic version.  It's generic, so don't get too hung up on the shape of the cross-shaft!  also, on f-body, the end of the shaft fits into a cup on the frame.  On the late 70's cars, the spring is necessary to hold that cup in place.  Up through 1974, the cup wouldn't just fall out, but starting in 1975, they saved 5 cents on a bolt and it'll just fall out and be lost.

The adjustment procedure is to loosen the adjustment bolt, put everything in park:
-transmission in park
-shifter in park
-Column in park (it'll stay there if you take the key out)
and then tighten it back up. 
check to make sure it starts in park and neutral, and the backup lights come on in reverse.

This is the same procedure for adjusting the floor shift cable.  There is a bit of slop in the linkage.  if the column doesn't operate exactly as you want it to, you may need to fudge the slop in it one way or another.  Also, the backup light and neutral start switch is able to be adjusted relative to the column, so you can adjust it independently from the key-lock feature.

1979-81 cars are different; the steering column has some sort of mechanical block that prevents the key from turning to "start".  Earlier columns had only an electrical switch.

Here's the manual 4-speed version:

This allows you to lock your steering wheel only while in reverse.  I guess they thought that was the least dangerous option.

The "neutral start" provision was moved to the clutch switch, so the backdrive linkage has no effect on starting a car with a manual transmission.
« Last Edit: March 08, 2021, 02:29:12 PM by firebirdparts »
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

langss

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #1 on: February 10, 2021, 09:22:38 AM »
Thanks for putting this up.

stormy69

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #2 on: February 11, 2021, 01:24:50 AM »
i want to say on my sons 81 z, you have to have the car in reverse for the key to turn to the start position, as well as in revers to remove the key when turning the car off.

Wallington

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #3 on: February 11, 2021, 01:32:53 AM »
because it's a manual.

firebirdparts

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #4 on: February 11, 2021, 08:13:06 AM »
i want to say on my sons 81 z, you have to have the car in reverse for the key to turn to the start position, as well as in revers to remove the key when turning the car off.

Thanks for posting this.  I was not quite sure how they handled that physical blocking interlock.  There are an awful lot of 1979 4-speed T/As that should be the same way.  I don't know if the columns are totally identical manual vs automatic, but I guess we could figure that out.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe


MalteseFalcon

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #5 on: February 11, 2021, 09:20:12 AM »
i want to say on my sons 81 z, you have to have the car in reverse for the key to turn to the start position, as well as in revers to remove the key when turning the car off.

Thanks for posting this.  I was not quite sure how they handled that physical blocking interlock.  There are an awful lot of 1979 4-speed T/As that should be the same way.  I don't know if the columns are totally identical manual vs automatic, but I guess we could figure that out.

Both of my 76 4-speeds, which I had when they were only a few years old,  were that way. But my '78 had the back drive removed before I got it. I've since found a replacement, but haven't installed it yet. 
Steve

1978 WS6 - W72 4 Speed, Martinique Blue on Light Blue - Fire Am Restification Project
 Build Thread: http://transamcountry.com/community/index.php?topic=684.0

2000 WS6 6-Speed Trans Am, Black on Ebony (sold)
1976 455 4-Speed Trans Am, Goldenrod Yellow on Saddle (sold)
1976 455 4-Speed Trans Am, Firethorn Red on Firethorn Red (sold)

firebirdparts

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #6 on: February 11, 2021, 09:52:45 AM »
Well, a 76 doesn't have anything to stop you from turning the key to start.  They changed that in 1979.  They just had something to stop you from turning it back to lock.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

MalteseFalcon

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #7 on: February 11, 2021, 10:37:55 AM »
Well, a 76 doesn't have anything to stop you from turning the key to start.  They changed that in 1979.  They just had something to stop you from turning it back to lock.

I was pretty sure that it had to be in reverse to start. But you have seen the '76 set up much more recently than I have, so I defer to you, Joe.
Steve

1978 WS6 - W72 4 Speed, Martinique Blue on Light Blue - Fire Am Restification Project
 Build Thread: http://transamcountry.com/community/index.php?topic=684.0

2000 WS6 6-Speed Trans Am, Black on Ebony (sold)
1976 455 4-Speed Trans Am, Goldenrod Yellow on Saddle (sold)
1976 455 4-Speed Trans Am, Firethorn Red on Firethorn Red (sold)

roadking77

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #8 on: February 11, 2021, 11:29:29 AM »
i want to say on my sons 81 z, you have to have the car in reverse for the key to turn to the start position, as well as in revers to remove the key when turning the car off.

Thanks for posting this.  I was not quite sure how they handled that physical blocking interlock.  There are an awful lot of 1979 4-speed T/As that should be the same way.  I don't know if the columns are totally identical manual vs automatic, but I guess we could figure that out.
I just redid the column for my 79 4 sp. It seemed like the same as the one for my 77 auto. I also have another tilt and a non tilt in the shop that are identical but dont know what they are from. I had assumed the one for my TATA was original, and it has all of the earmarks to make me think so, BUT I cannot say for sure as it was loose and the date code on the horn button says otherwise. Anyway, from what I can tell the only difference is in the neutral switch at the base of the column.
Finished!
77 T/A - I will Call this one DONE!
79 TATA 4sp-Next Project?
79 TATA - Lost to Fire!
86 Grand Prix - Sold
85 T/A - Sold
85 Fiero - Sold
82 Firebird - Sold
'38-CZ 250
'39-BSA Gold Star
'49-Triumph 350
'52-Ariel Red Hunter
'66-BSA Lightning
'01-HD RoadKing

djustice

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I did solid body bushings on the frame, and now the backdrive linkage wil not reach, i have ziptied the linkage to speedometer cable for now.
i have bougth a lokar linkage that is lying in my trunk, i have not gotten around to mounting it yet, but i am not sure it will work as intended as i need to keep the shift cable bracket but add the bracket for the lokar linkage. 

i hope hotlinking these images work:


and



need to fit on the shifter shaft together without interference.

I will have access to the car sometime in April after i get it out of winter storage.
« Last Edit: March 08, 2021, 08:44:00 AM by djustice »
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

firebirdparts

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #10 on: March 08, 2021, 02:32:09 PM »
That ugly lever could have enough arms to do all the jobs it needs to do, but you may not be fit both.  I don't know. 

The factory linkage is amazingly awkward compared to the Lokar, but I guess there's bound to be a good reason for that.  I don't know what it is, though.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Wallington

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #11 on: March 08, 2021, 07:43:43 PM »
Anti-theft? It's hard to climb under a factory car and move rods that run against the direction they travel, compared to direct back and forth replacement. I don't have it, RHD car, only guessing.

TammyTA

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #12 on: March 09, 2021, 03:18:57 PM »
Don't think the Lokar linkage would work on a bird.  Arm would need to be much longer to bypass the firewall.  Hope I'm wrong, as it would be a slick replacement.  Took a while to track down all the original parts on mine.

djustice

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Re: Backdrive Linkage: How the steering column is linked to console shifter
« Reply #13 on: March 09, 2021, 04:04:01 PM »
The rod in the illustration photo above is cut to length, it is a bit longer and is ment to be cut and bendt to the application. Lokar aca-1800 is made for  TH400 (and a few others)

My other alternative is to use a die and cut threads on the end of my existing linkage end and use a threaded rod and coupler to lengthen it, i think that is a little to shady three approach, but could work.
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.


 

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