vibration at 20-30 mph

[Ron Perry]

My 64 Sedan De Ville has a vibration starting at 20 and stops at 25 to 30 mph before that and after that car runs smooth. Thinking it might be an exhaust vibration I put a little sill glide silicone on the rubber hangers which are only 10 years old and in very good condition. This did not help. There is no vibration when car idles or when I rev it up. The car runs and shifts great. I have just recently noticed this vibration. I have owned this car for over 10 years I bought it with 18000 miles which really are original and now have 21000+ miles on it. The condition of this car is mint inside and out point being it's not beat. It's all original, I have done a lot of mechanical things but have never touched the drivetrain. Any thoughts would be much appreciated. Thank you, Ron Perry, the only other thing I might add is the vibration seems to be coming from drivers' side, but it is really hard to determine.

[Kurt]

It could be a few things. Probably the most common cause is drive line angle. The angle shifts when motor mounts, especially the transmission mount collapse. This discussion comes up often. You can use the search function (upper right-hand corner of this page) for search terms like "drive line angle" or "rumble" etc to see previous discussions. I'd check the condition of the transmission mount & go from there.

[Michael Vogler]

This is a great post.  I get a noticeable vibration at about 40 mph which stops at about 44 mph. I've had my mechanic look it over a number of times and we have been unable to locate it source of the vibration.  My mechanic has suggested that, although my tires are in great condition, they are quite old (2009), which suggests the car had been sitting for quite a while, and seems to have produced a very slight bulge in the tire from where it sat.  Once my car gets out of the paint shop, I'll be putting new tires on her. I hope that cures the problem. If not, I'll be having my mechanic inspect the drive train and rubber.

[Ron Perry]

I want to thank everyone for all the great replies to my post. All of your information has been very helpful. I did look at all my rubber components first based on cars condition and age seems the most logical place to start. I did notice some fine cracks on the transmission mount, but engine mounts look ok. I also looked as best I could at the rubber bushings at the rear of car and did not see any noticeable cracks. My tires are over 10 years old, but tread is excellent so that's another spot for me to look. I have my work cut out for me! Thanks again to everyone Ron Perry

[3ft7bqmb7dryo]

Starting front to rear; Collapsed trans mount, worn tail shaft bushing, bad carrier bearing or support, worn CV joints, worn bushings in the lower control arm. ( the rear bushing gets distorted and allows the pinion angle to change) Unbalanced drive shaft.  Bad rims/tires,