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1976 Mark Vibration

Hi Bill,
A few months ago the clutches in the trans started giving up and I had my trans people do a full rebuild.
The trans shifts perfectly again, smooth and sure… BUT, when picked up the car I now have a bad vibration at 1750 rpms. ( or driving at 45-50 mph. ) its not drive-line related at its there without the car moving. It’s in the seat, steering wheel etc… like an electric toothbrush on on steroids. VERY harsh.
First order of business was to swap in a NEW, not rebuilt torque converter with absolutely NO CHANGE.
You would think that when you hold it at 1750 ( in park ) rpms a exhaust pipe was bent into the crossmember but that’s all OK too. When you go above 1750 rpms Poof it completely disappears… come back down its there…. or drop to 1700 and its gone too.
When I put a tach o the car, set idle to 1750 rpms, lay under the car and put my hand on the crossmember it is buzzing horribly (all mounts are new too) I have none of this sensation on my 72 – IV. I don’t particularly feel it in the trans pan, more though in the center of the trans case itself.
We are going to pull it all again, remove the converter and throw a couple of bolts in the transmission to run car to isolate the trans from turning.
If the vibration is still there they want to have another flywheel on hand to swap in as a test to rule that out while they are there.
My question for you is, I want to have a flywheel on hand. Should I go with a new or used part to swap in. Regarding the trans rebuild, anything you can think of that would vibrate in there? Is there a gear that could have gone in the wrong was, something too tight in there? Could worn gears that wore together then get assembled in another orientation cause this?
Again, Hope you are enjoying the winter in Florida, I really appreciate your time and knowledge.
Hi Richard –
If the flywheel is proven faulty or is damaged somehow, it should only be replaced by a NEW FORD supplied replacement if available. A correct used one should only be installed it is absolutely “Known” to be a good one in all respects.
I would have no idea what is causing your vibration without having the vehicle here to inspect. I would place the vehicle on a front end alignment style of ramps so as to have the wheels supported as they would be on the ground. The vibration could then be checked properly at 1750 rpms from underneath. I will say however that in this case if this issue was created by the transmission overhaul and the same technicians are now checking it for you , that is the best way to go. If we can help you further please contact us at any time.

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