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Clunking transmission


Joseph Colavito
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I’m interested in a nice ‘57 T-Bird. The car has some minor issues that don’t concern me. But the pronounced CLUNK that occurs when The Ford-O-Magic 3 speed is shifted into Drive or reverse worries me. Some have said this is characteristic but I don’t believe this degree is normal. What could it be and what can be done about it?

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Unlikely to be a big deal. Idle set too fast will cause it. Make an offer with a price adjustment…..say 4-5 k, and see what they say. That should get you covered for most issues.

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Having quite a bit of experience with that transmission family, and none of it good, I would be way more concerned about whether the transmission shifts and works properly, that it is not full of burned stinky fluid, and that reverse works and works normally.

 

The clunk is backlash in the driveline. It is almost certainly not the transmission. As previously mentioned, idle speed matters. I'd set the idle speed and mixture to the specs in the manual, check the u-joints for looseness as they are probably bad and mostly responsible if it is loud, replace if necessary. Whatever portion of the clunk is due to backlash in the rearend I would just live with. The clunk is probably not going to disappear completely.

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All the joints were checked, fluid good, shifts through gears fine.  Idle speed at 600 rpm’s. All the obvious were eliminated, motor and transmission mounts, etc. The clunk is very pronounced, jolting the car as you shift from drive to reverse while sitting still. The owner came down 1K but I don’t think he will do any better. Perhaps I should look for a standard. I would rather have that anyway.

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Stick shift cars are out there but are a little harder to find since 85% of the early T-Birds were automatics. If you go in that direction get one with overdrive. That will most likely be a “D” code car. The “C” code cars were strictly 3 speed with no overdrive. This is for 1957. Personally I have the automatic and prefer it for this type of car. If it was a Miata I would want a 5 speed manual.

Lew Bachman

1957 Thunderbird with Ford-O-Matic drive

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Could also be the rear end. If there is excessive play in the diff such as worn out thrust washers behind the spider gears or pin hole worn oblong. Check how much you can turn the driveshaft back and forth.  Not likely a big expense to fix if it runs quiet.

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On 11/20/2022 at 5:38 PM, 1957Birdman said:

Stick shift cars are out there but are a little harder to find since 85% of the early T-Birds were automatics. If you go in that direction get one with overdrive. That will most likely be a “D” code car. The “C” code cars were strictly 3 speed with no overdrive. This is for 1957. Personally I have the automatic and prefer it for this type of car. If it was a Miata I would want a 5 speed manual.

Lew Bachman

1957 Thunderbird with Ford-O-Matic drive

 

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No, my car does not clunk when I shift it into reverse or drive. What are the RPMs at idle of the car that you are looking at? If the tach indicates over 900 RPMs at idle it is too high and should be reduced. The shop manual says 550 RPMs, but my car seems to run better at 700 RPMs. I am also inclined to think the U-joints are part of the problem. Do you have any idea how many miles the car has on it? I know with cars from the 1950's it is hard to tell because many times the speedometer was rolled back. Definitely check the transmission fluid. If it nice and red and not burned smelling than I would think the clunk is not a transmission problem.

One last suggestion, contact the CTCI chapter near you and see if someone from the club that is knowledgeable about these cars could look at it with you. A second opinion would definitely help here from someone who knows these cars.

Lew Bachman

1957 Thunderbird

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