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1955 Plymouth Powerflite Vibration Source?
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Stevie Exit
Posted 2018-09-29 7:07 PM (#570920)
Subject: 1955 Plymouth Powerflite Vibration Source?


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Posts: 19

My mechanic is recommending that I have my transmission rebuilt as he has no other ideas about what might be causing my vibration problem. This is a problem that has plagued my car since it was put back into service in the early 1990s. I would really like to get it fixed. When driving my car there is a vibration that can be felt in the steering wheel peaking between 35 and 45 mph. Below 30 mph things are smooth, and above 50 mph things are smooth. It is almost like two different frequencies beating against each other because at constant speed the vibration gets stronger and weaker in a repetitive fashion. We tried a new drive shaft, and different transmission mounts. They had no effect. The engine is eliminated because the transmission can be dropped into neutral at 40 mph and the vibration is still there. We removed the driveshaft and ran the engine with the transmission in drive (up on a lift). There was a strong vibration when the transmission was in second gear running the same speed range on the speedometer. I called a vintage transmission rebuilder and he said he had only ever seen one transmission causing a vibration, and it had been visibly damaged at the output shaft. He didn't think a transmission would be likely to cause my problem. It will be expensive to rebuild my transmission, and I'm not sure that it would be corrected by a normal rebuild process. My car has 58,000 miles and the transmission shifts properly. Any suggestions? (The front motor mount was replaced when the car was put back into service so it should be OK.)

I don't remember any vibration problems when driving it in the early '80s. It sat abandoned for about a decade, and even in the early 90s I drove it 20 miles to be repainted I didn't notice anything. After that I made quite a few changes to the car-- engine rebuild, driveshaft rebuild, new bias ply tires (replace again last year), new motor mounts, parking brake repair (it kept slamming on while I was driving.) I think if I could get this vibration issue fixed I would be able to drive my car to some long distance shows.
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Shep
Posted 2018-09-29 9:16 PM (#570923 - in reply to #570920)
Subject: Re: 1955 Plymouth Powerflite Vibration Source?



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So only in gear, never in neutral? It is speed sensitive, not rpm sensitive? There is no second, you mean high gear, no?
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56D500boy
Posted 2018-09-29 9:20 PM (#570924 - in reply to #570920)
Subject: RE: 1955 Plymouth Powerflite Vibration Source?



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I would suspect the wheels/tires before anything else at this point. Is there another set of known to be good wheels/tires you could try?



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Stevie Exit
Posted 2018-09-30 7:54 AM (#570941 - in reply to #570920)
Subject: Re: 1955 Plymouth Powerflite Vibration Source?


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Posts: 19

Shep, second gear meant high gear. I really don't think it does it in low gear, but the engine is spinning so fast the noise could be confusing me.
5D500boy, I can ask a friend if I can borrow some tires. I have tried swapping the tires from the front t the back, swapping my spare in and out, and just recently new tires (Goodyear Supercushions). None of them seemed to make a difference.
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Shep
Posted 2018-09-30 10:12 AM (#570946 - in reply to #570920)
Subject: Re: 1955 Plymouth Powerflite Vibration Source?



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Location: Chestertown, NY ( near Lake George)
Rear wheels of the ground safely, helper in the car gets it it the point the vibration is there, you should be able to feel the source by comparing at what point in drive it is most obvious. If it occurs under these conditions, you pretty much rule out tires, as I said it is critical to determine if it is rpm or speed sensitive.
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57chizler
Posted 2018-09-30 12:17 PM (#570958 - in reply to #570920)
Subject: RE: 1955 Plymouth Powerflite Vibration Source?



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Stevie Exit - 2018-09-29 4:07 PM

We removed the driveshaft and ran the engine with the transmission in drive (up on a lift). There was a strong vibration when the transmission was in second gear running the same speed range on the speedometer.


I'd say that eliminates the tires and the rest of the rolling parts.
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56D500boy
Posted 2018-09-30 12:41 PM (#570961 - in reply to #570958)
Subject: RE: 1955 Plymouth Powerflite Vibration Source?



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Location: Lower Mainland BC
57chizler - 2018-09-30 12:17 PM
Stevie Exit - 2018-09-29 4:07 PM
We removed the driveshaft and ran the engine with the transmission in drive (up on a lift). There was a strong vibration when the transmission was in second gear running the same speed range on the speedometer.


I'd say that eliminates the tires and the rest of the rolling parts.



I agree. I must have missed the driveshaft off test when I suggested the problem might be wheels (bent/out of round) and/or tires.

Seems strange that the issue is internal to the Powerflite. Then again, there are just a few parts in there.



Edited by 56D500boy 2018-09-30 12:56 PM




(55-56PowerFliteCrossSection.jpg)



(55-56PowerFliteBlowUpPartsDiagram.jpg)



Attachments
----------------
Attachments 55-56PowerFliteCrossSection.jpg (191KB - 16 downloads)
Attachments 55-56PowerFliteBlowUpPartsDiagram.jpg (237KB - 15 downloads)
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Shep
Posted 2018-09-30 12:54 PM (#570962 - in reply to #570961)
Subject: Re: 1955 Plymouth Powerflite Vibration Source?



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Posts: 3092
20001000252525
Location: Chestertown, NY ( near Lake George)
I've rebuilt a few Pf's in my shop, and I don't see a source that would cause this in a properly operating trans, maybe the convertor.
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