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 Transmission / Driveline and Traction
 THM400 Linkage Adjustment
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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 04 Aug 2014 :  6:59:15 PM  Show Profile  Reply with Quote
Dear Pontiac Aficionados,

With my transmission gearshifter in 'Park', my '72 Firebird can be rolled forward or backward. The car has been in storage since 2007 and I've started a full restoration a couple of weeks ago. I've installed new PU engine brackets and a transmission mount, so I figured I messed up the linkage.
After I had disconnected the steering column shifter rod (the car has a console shifter, though the transmission is also linked to the steering column) and tried to select the gears directly by turning the lever manually, I found out that only 'Low', 'Super', 'Drive' and 'Neutral' have a clearly defined lever position, whereas 'Reverse' can only be selected by rotating the lever beyond 'Neutral'. I don't know if 'Park' can actually be selected, since the only way I can make the tail shaft lock up, is by excerting as much force on the lever as possible with one hand while rocking the drive shaft clockwise and anti-clockwise with the other, till an audible click confirms the shaft has been locked effectively.
Does this mean the 7 years of inactivity have taken their toll, indicating a full rebuild is in order, or might there be another cause? I cannot drive the car, since a nasty carb valve screw has ruined 2 cylinders, though I just would like to get an idea of the additional budget damage the transmission is going to inflict. Right now, it's relatively easy to yank it with the engine. If I leave it as is, chances are not being able to select 'Park' from within the car is only one of the transmission issues that arise once I fire the car back up, hopefully not in the too distant future.

Thanks a whole lot in advance for your thoughts and concern.


Brgds,

Rick

Blued and Painted
Chief PONTIAC

USA
3409 Posts

Posted - 04 Aug 2014 :  10:02:44 PM  Show Profile  Reply with Quote
Park is achieved with a parking paw that mechanically locks a hub on the output shaft to the trans case. It's not related to the forward or reverse operation of the transmission. Sounds to me like the cable adjusting nut has come loose or the cable is out of adjustment or damaged. Place the floor shifter in park, then go under the vehicle and loosen the cable to lever adjusting nut, then manually move the trans lever towards park position. Confirm again the drive shaft is locked. Tighten adjusting nut and check operation.
Also the crimped ends of the shift cable can pull apart creating slack. If so the cable would need to be replaced.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 04 Aug 2014 10:05:23 PM
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Phil
The Great White Buffalo

USA
7222 Posts

Posted - 06 Aug 2014 :  04:58:43 AM  Show Profile  Reply with Quote
Your explanation is not entirely clear as to whether you disconnected the shifter cable while you were manually moving the transmission shift lever?. If not, try disconnecting the cable from the lever first. Then try moving the lever through the entire range while you "count" the positions in your head.

It's entirely possible the shifter detents are out of sync with the trans detents (requiring simple adjustment) and if you were trying to move the lever with the shifter cable still attached you would also be fighting against the shifter's lockout from N to R and R to P.(requires button depression) as you can't have one hand at each end simultaneously.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.

Edited by - Phil on 06 Aug 2014 05:01:01 AM
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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 07 Aug 2014 :  10:35:45 AM  Show Profile  Reply with Quote
Dear Pontiac Aficionados,

You are right as far as the connection to the console shifter is concerned: I forgot to disconnect the flooshifter linkage, making it extremely hard to manually overcome the tension of the mismatched shifter and transmission levers. With the linkage unhooked, it's easy to manually select all transmission positions. Which leaves only one question: do I reconnect the linkage with all levers in 'drive', 'neutral' or any other position?

Thanks a whole lot in advance for your help and support.


Brgds,

Rick
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