If due to the drive shaft angle, this vibration will only occur at the lower
speeds. This can usually be corrected by adding or removing shims between the
center bearing in the drive line and its mounting point.
If there is a vibration, and there is a pile of shims in that location, the
vibration will probably go away if you remove them. This has been the case with
the two cars I had that did this. They were my '56 and my 1960 Custom.
The '60 did it after my father replaced the rear leaf springs with heavy duty
leaves, and also added an extra leaf. Thusly, he raised the back of the car
higher than its original position. That caused the out-of-alignment condition.
The '56 did it when I first bought it, but I noticed that it would go away when
there were several people sitting in the back seat. When I removed the shims it
smoothed out and never vibrated whether loaded or unloaded. It also had both
rear axle support struts broken out, but the vibration was still there when I
had them repaired.
I think that this happens because there may have been additional shims between
the rear axle support struts, and their mounting points. At some time in the
car's history, the struts had become broken, and the shims lost or discarded,
throwing the whole thing out of wack. I have seen many Imperials where these
struts were broken. I think there were shims in all three positions on the '56
models (first year of split drive line), but I think that they are mainly found
under the support bearing on the newer cars.
Basically, if you raise the rear end, you have to take out some or all of the
shims under the support bearing. The angle can be checked by following a
procedure in the shop manual.
Paul
In a message dated 8/19/2004 5:47:22 PM Eastern Daylight Time,
GKitterma@xxxxxxx writes:
>Thank you for bringing up this issue Phillipe.
>
>I am getting ready to attack this very same problem on my '56 C-73
>
>It has a different system for adjusting the U-joint angle and propellor
>shafts, but I believe the alignment issues are the are the same as your '57.
>
>Last week I pulled the rear axle and springs for cleaning, repair, and new
>rubber bushings, etc. After reassembly the car sits level or perhaps a 1/4"
>higher @ the rear. We shimmed the axle so there is no twist on the springs (
>your
>car is different; shims do not cause spring twist). Next week I go back to the
>shop with spirit level protractor in hand to address the U-joint alignment
>problems which are causing the drive line vibration in my car. My problem is
>at
>a maximum between 20 and 40mph. I haven't had my car up to 80 yet, so perhaps
>there is a period or node in that range too.
>
>Keep us up on your progress and I'll try to do the same.
>
>Gary Kitterman
>1956 C-73 "Babe"
>
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