59 Cadillac Vibration

[Jeff Wilk]

Any ideas on what to look for on my 59 Sixty Special?  Car starts with a flip of the key....engine idles like a clock and is as smooth as glass from 0 - 30(ish) and from 45 and above.  But between 30(ish)mph and 45(ish)mph it has an aweful vibration.  Not coming through steering wheel though and feels/seems like it must be in the drivetrain....I think? Any ideas on where to start diagnosing?

Shaking Jeff........

[vicbrincat]

Jeff,
It could be a quite a few things.
1. Check to see if the center driveshaft hanger/support is worn out. That would cause vibration.
2. Check your U-joints and make sure that they are not worn out.
3. it is possible that that flywheel may be out of balance (less likely)
4. It is also possible that the fluid coupling (I believe it is known as a torous...sp?) is out of balance.

Has the drivetrain recently been rebuilt?

Vic

[Otto Skorzeny]

What happens above 45mph? Does it keep vibrating or does it smooth out?

How is the engine running when the vibration occurs? Can you tell if it's missing or stumbling?

Check also each tire for proper inflation and for tread separation or other flaws. Have they been balanced and rotated recently. Switch them around to see if there is any difference.

Did this vibration just start or has it always done this since you've owned the car? Did it start suddenly or were the symptoms gradually getting worse?

[Jeff Wilk]

Thanks I will check each of these out.  The drivetrain is all original, but it has sat untouched or started for 25 years in my garage.

Jeff,
It could be a quite a few things.
1. Check to see if the center driveshaft hanger/support is worn out. That would cause vibration.
2. Check your U-joints and make sure that they are not worn out.
3. it is possible that that flywheel may be out of balance (less likely)
4. It is also possible that the fluid coupling (I believe it is known as a torous...sp?) is out of balance.

Has the drivetrain recently been rebuilt?

Vic

[Jeff Wilk]

Thanks for the ideas.  I've had the car for 30+ years.  The drivetrain is all original.  Above 45 it all smooths out.  At this mid range though it vibrates and does not feel like an engine miss.  The tires are all brand new and balanced. I was thinking transmission? as that has not been touched at all nor even drained since we got the car started in the spring after sitting for 20+ years in my garage.

Jeff

[Otto Skorzeny]

It would probably be a good idea to drain the trans fluid and replace the filter regardless of whether or not you can definitively pin the problem on the tranny. I would use one of the transmission products like Seafoam to loosen up any crud and then drain it completely. Add new fluid and filter.

While you're under there inspect the drive shaft for dents or bends and check and lube all the U-joints. Yank on the joints, etc. and look for any unusual slop or movement.

You might also try raising the rear end off the ground and observing what happens as you shift into gear and accelerate. First, does it do it with the wheels off the ground?

Can you see any wobble in the driveshaft as it turns?

[Art Woody]

Before you do anything, check to see if if you have a vibration without driving it.While in park, slowly press accelerator and bring up the rpm's and check for vibration there. Then put trans in gear and hold brake,  slightly accelerate engine and observe for vibration, and check for motor mount,  or trans mount breakage or looseness. This could eliminate a few drive train issues. Art woody

[william_b_noble]

I had exactly these symptoms on my 59 - I had the harmonic balancer and the driveshaft center support rebuilt, and I replaced the center bearing, and had the driveshafts balanced.  After that it was much much better.