Mystery vibration in 36 Ford

[collinrestores]

I've been slowly restoring this 1936 sedan after getting it last year. After an extended saga of trying to stop it from overheating, now the main issue I'm worried about is this persistent vibration being produced by the engine.

Let me describe the vibration and then explain why I'm worried.

-always present, but has harmonic points at regular intervals as you rev up the engine
-present whether the clutch is engaged or not, and whether the car is moving or not
-is bad enough to shake the cab at the harmonic points
-becomes much less noticeable if you keep revs low and don't floor it while accelerating
-seems to be getting transferred almost completely to the frame of the car for some reason. If you rev up the engine to make it vibrate, the frame and body of the car are vibrating but the engine is not.
-becomes sharper, but not necessarily "worse", under load. That is, you can feel it in your feet on the floor as a sharp rap rather than a rumble, when the engine is under load.

All this says flywheel or crankshaft to me. If it's the flywheel, I'm not too concerned. It would probably need to be balanced at some point, and it's not too bad until then. If it's the crankshaft, or bearing caps, then I'm worried. If one of those caps is cracked, maybe that would explain why it seems to get worse under load? And if so, I want to fix that ASAP lest it fail and the crankshaft have a bad day.

The other issue here is that when I replaced the front motor mounts, I put the rubber in upside down by mistake, because the old mounts were so squished that I misunderstood how they were supposed to go in. But the vibration was present before I changed them, and I don't think they'll make much of a difference when I flip them the right way up.

I also added some rubber padding to the rear engine mounts, on the transmission, which were bolted directly to the frame (great idea, Ford).

I know in order to check the crankshaft I'll have to drop the pan. Problem is, in this model year, from what I've heard it's hard to do this without basically pulling the engine. I don't have the ability to pull the engine with the tooling I have in my little one bay garage. I can maybe jack it up a ways with my floor jack. FWIW I was able to replace the radiator, but that was a bear and required an extra set of hands.

Anyone have any gut feelings about this?

And if anyone is in Colorado and wants to see the car or help me replace the clutch (that'll need done at some point), let me know!

[big job]

Most likely the pressure plate

[Charlie ny]

The trans mount should be attached directly to the cross member. There is a 'rubber'

bushing vulcanized within the mount. The inner portion of the mount attaches to the trans and outer portion to the cross member. Separating the inner and outer is the
insulating 'rubber'.
OK
I had the same issue with my '35 after I installed a new clutch which I had balanced.
My motor had been balanced after a rebuild in it's distant past. After some shade
tree advice from an older Ford guy I removed the trans and blocked up under the pan.
I rotated the PP 120* then 240* and found one of those the vibration was less....
still there but less. I'm not joshing here......I then used a longer PP attaching cap
screw and right sized brass bushing for a bob weight and sequentially moved the long cap screw and bushing to the six PP attaching holes. One the six positions made things quite acceptable...not perfect. I was 60 at the time and did the whole schmeer in a day.
If you proceed in this manner be SURE the motor and car is well blocked and wear no loose garments....That PP spinning is lethal.



Charlie ny

[motordr]

Check the diameter of the fan pulley, I believe in the 1934 model they had an issue with harmonics that was solved by going to a larger diameter pulley, if I remember, from about 3 7/8” to about 4 1/8” diameter.

[collinrestores]

I'm going to have to figure out how to check that pressure plate. I can get to the inspection cover on the transmission, does anyone know if there's an easy way to check the PP from that vantage point?

And I forgot to mention, wrt the fan pulley, I already tried removing the belt and running the engine a bit to see if it was the fan or the water pumps. No dice, vibration remains.

[DavidG]

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Just so there is no confusion, it is the rear transmission mount that is bolted directly to the chassis frame, but within the construction of the original transmission mount there is no direct metal-to-metal contact as the parts are isolated by a semi-hard rubber ring.l If your rear transmission mount is missing that rubber insulation ring or it is deteriorated to the point where metal-to-metal contact exists, it should be replaced. There is a good reproduction of the original available.

[AnthonyG]

While I would tend to agree Big Job on the pressure plate as a potential I’ll relate I had exactly the same symptom / issue on my ‘35 while building. It turned out the original engine builder had installed a converted flywheel by re-drilling the threaded mounting holes for the pressure plate. Those holes were over .060” out of concentric causing the vibration. Caused same symptoms. I spent over a month chasing ghosts before a FB friend w a shop figured it out.