Rhythmic vibration 1955 T-Bird

[zeroroadkill]

New U-joints
Balanced drive shaft
Output shaft seems tight
I get a rhythmic vibration at 50mph you can feel in the seat of your pants
New tires, balanced, aligned
Motor stabilization new bushings and no engine weight on them
Engine runs smooth
Neutral stops it so not running gear or rear end

ideas?

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[64ZCODE]

I would think an engine compression check is in order.

If engine compression checks out then problem likely with ignition system, possibly defective plug(s), spark plug wire arcing to engine or frame, defective/worn out distributor cap/rotor, defective condenser, worn out coil, short in system. Some of these cars, and I'm not clear on which ones, came with a transistorized ignition system. Is that the case with this car, or does it have points ignition system? My '64 had points and the engine would misfire at higher revs. I installed the Pertronix III ignition module, hotter coil and MSD spark plug wires and no more misfires and engine has more power.

 

[zeroroadkill]

All 115-125lbs
Pertronix
New plugs, wires, rotor, cap, coil
Runs smooth, idle smooth, great power, no misfires.

 

[jack-in-sac]

If engine compression checks out then problem likely with ignition system, possibly defective plug(s), spark plug wire arcing to engine or frame, defective/worn out distributor cap/rotor, defective condenser, worn out coil, short in system. Some of these cars, and I'm not clear on which ones, came with a transistorized ignition system. Is that the case with this car, or does it have points ignition system? My '64 had points and the engine would misfire at higher revs. I installed the Pertronix III ignition module, hotter coil and MSD spark plug wires and no more misfires and engine has more power.

No they did not come with transistorized ignition in 1955. You will not see that in Fords until well into the 60s.

 

[Douglemmo]

You say neutral stops the vibration if that's correct then clearly it's in the engine possibly the transmission.so please clarify if you were driving at 50 mph and the vibration was occurring and you pushed in the clutch or shifted the transmission into neutral the vibration would immediately stop. is that correct?

 

[Ward 57]

Sounds like a flywheel out of balance or even the harmonic balancer. There are rebuild ads all over the place to rebuild harmonic balancers. I've never had the problem but there must be a reason for an advertised market.

 

[zeroroadkill]

You say neutral stops the vibration if that's correct then clearly it's in the engine possibly the transmission.so please clarify if you were driving at 50 mph and the vibration was occurring and you pushed in the clutch or shifted the transmission into neutral the vibration would immediately stop. is that correct?

Yes

 

[64ZCODE]

You say neutral stops the vibration if that's correct then clearly it's in the engine possibly the transmission.so please clarify if you were driving at 50 mph and the vibration was occurring and you pushed in the clutch or shifted the transmission into neutral the vibration would immediately stop. is that correct?

That's how a worn or defective U-joint behaves. Vibrates under load.

 

[zeroroadkill]

As i stated
New U-joints
Balanced drive shaft

 

[64ZCODE]

So zeroroadkill, when did this vibration start? Was it after replacing components as you outlined above? Or is this a long term problem you've been pursuing fixes for?

 

[zeroroadkill]

The problem was there that’s why I decided to replace the U-joints and have the driveshaft balanced

 

[doug7740]

New U-joints
Balanced drive shaft
Output shaft seems tight
I get a rhythmic vibration at 50mph you can feel in the seat of your pants
New tires, balanced, aligned
Motor stabilization new bushings and no engine weight on them
Engine runs smooth
Neutral stops it so not running gear or rear end

ideas?

Since you said that you can feel the vibration in the seat of your pants and in neutral the vibration stops, I would check where the exhaust pipes pass through the frame. I had a similar problem a few years back and it turned out to be the rubber exhaust hanger strap had stretched from age, causing the exhaust pipe to contact the frame under certain load and torque conditions. Replacing the rubber hanger straps corrected the vibration problem.

Since a picture is worth a thousand words, see the attached pictures.

doug7740
1955 Thunderbird Blue

 

[biddle]

@doug7740 I inserted the photos as full-size images into your post.
Tutorial if you want to see how-

 

[flamejockey13]

OK, if you haven't figured out your vibration yet here's something else to think about. If the transmission and differential are not parallel it can give you a harmonic vibration under load that pulses from fainter to stronger every second or so. They can get out of whack with bad engine or trans mounts and if the rear axel has rotated a bit on the springs. Place car on level floor and use level to check tranny pan and differential. (Diff is tough but they usually have a small flat on the bottom near the pinion shaft) . At best they should both be level with the floor or at least the same amount off in the same direction (parallel). They make a fairly cheap ($20 on Amz) magnetic digital level that works great.