One other thing to consider is the possibility that one or more tire is out of
round. If the tire (or wheel) has axial runout, ordinary balancing doesn't do
anything. A "road force" balance machine can offer some compensation but if the
tire is significantly out of round, only replacement will solve the problem.
This turned out to be the source of a bad vibration on my pickup. After a
heated discussion with the tire store, they agreed to replace the tire. As a
stopgap measure, they road force balanced the bad tire and it did help. The
road force balancing method is also commonly recommended for cars that are
prone to vibration (e.g. Porsche 911 - wide tires, no power steering).
Hope this helps - back to lurk mode,
Brian
-----Original Message-----
From: owner-mg-t@autox.team.net [mailto:owner-mg-t@autox.team.net] On Behalf
Of Stuart C. Keen, Jr.
Sent: Monday, July 18, 2005 10:11 AM
To: MG
Subject: TD Vibration Revisited - a brain teaser
AS PREVIOUSLY REPORTED, I have put Dayton 60 spoke chrome wire wheels on my
'51 TD. Tire-on-vehicle spin balancing of wheels not available anywhere
(liability issue). The wheels have been electronically balanced by 3
different companies. The last was accomplished by MG Repair in Tampa who
also realigned the front end (they had a wire wheel hub mounted on their
wheel balancer for accuracy). They also checked that the front end (tie rods
etc.) was tight, no play in the steering rack and pinion system, and front
Girling shocks good. I personally checked later that the 3 rubber bearings
used in the steering column coupling were good - i.e. that there was no play
between the column and the pinion shaft.
FACT: There is minor vibration of the steering wheel between 52 and 57 mph
(rapidly oscillating in a tight arc, approx 3 degrees). I could live with
this, but would like to eliminate. It was not there when I had the original
disc wheels mounted (though they also had to be balanced THREE TIMES to
eliminate the same vibration). I have rotated my Coker 165R15 tires with
radial tubes three times, but this has not changed the vibration. Spun the
wheels, all treads appear to be true - no weaving back and forth. Checked
wheels, max movement about 1/16 inch.
It doesn't seem to be the body itself vibrating (not felt in doors, nor
noticed at the dash), though I do detect vibration in the windscreen when
the steering wheel is vibrating? Since the body doesn't seem to be
vibrating, I am pretty much ruling out drive shafts and other components.
THE BRAIN TEASE is this. Above the steady rapid vibration from 52 to 57 mph,
I get an even more modest but noticeable vibration (slight, less rapid
shaking of the steering wheel). But this is cyclic. The vibration peaks and
then damps out until there is nothing, and then peaks again. The time
between peaks is almost exactly TEN SECONDS. For five seconds I can feel the
vibrations building up to a peak and then diminishing, then there is nothing
for the next 5 seconds. Then it repeats. It appears at ANY SPEED above 57
mph, or at least at 62, 65 and 67 mph which I just tested on the interstate.
Neither road surface condition nor wind condition made a difference.
What the heck on the TD would cause cyclic vibration?
What is causing the steering wheel to vibrate more at 52 to 57 mph?
Thanks for any suggestions or recommendations (no, I will not remove the
wire wheels - they look just too cool with the wide whitewalls as judged by
the comments I have received).
Stu Keen
'51 MGTD Mark II
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