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Vibration on MGB

To: british-cars@autox.team.net
Subject: Vibration on MGB
From: paulg@cme.nist.gov (Paul Gilders)
Date: Mon, 16 Nov 92 10:07:45 EST
Hi folks,

        Just thought I'd try to probe for a little collective net
wisdom before I spend too much time using diminuishing brainpower in
the wrong area. Basically my problem is thus - about 1.5 weeks ago, my
MGB began to develop an annoying vibration. This vibration occurred at
between 2000-2500 revs and seemed to find the resonant frequency of
every poorly attached bit of trim in the car (ok, so this includes
just about every component). Anyway, the performance of the car
appeared to suffer also - almost like it was severely pinking. I was
originally suspicious of poor quality fuel, but having changed the
fuel completely and still experiencing the problem I can rule this
out. So next I thought I'd try and retard the timing a little, but
with a complete loss of performance, therefore deciding to leave it at
the original setting. Pulling the plugs out revealed a slightly week
mixture on all cylinders, but not so drastic that I would expect such
a juddery acceleration without complete loss in performance.

        So my mind is now thinking about other roots of this
vibration. Maybe I should be looking at the drive shaft and U joints?
Has anybody experienced anything like this before, and can they
recommend some tests that I can do to check various components. I know
that these types of judders can be very deceptive - often occurring at
places unthought of. I originally thought engine, because the problem
appeared to occur over a specific rev range, but now I'm not so sure.
Once I get above 2600 (about 50mph and above) the juddering completely
disappears and the car cruises beautifully. 

        Ok, so any advice or ideas would be greatly appreciated.

        Thanks,

        Paul.



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