[Vintage-race] Driveline angles and vibration? (General, but in my Lotus Seven)

[John Donohoe]

For years I've struggled with a vibration in the Seven that seems to come and
go at various speeds, and is the same regardless of wheels (I've run 2 types
of steel and one set of cast aluminum wheels all resulting in the same
vibration). I balanced the driveshaft, and checked the u-joints, all good.
Today I stumbled across this instructional booklet on drivetrain
alignment: http://www.iedls.com/IEDL_PTS_LGL_091008_Secure.pdf and now I
wonder about checking the alignment between my engine and differential pinion
shaft. When I got the Seven, the the BMC smoothcase gearbox was attached to a
Sprite mount, which was bolted straight to the aluminum floor of the
transmission tunnel with a single large bolt! This also resulted in the
bellhousing clunking against the lower, curved firewall frame tube over every
bump, and yes, the vibration was horrible on the 6 inch wide, custom Lotus
steel wheels that were on the car when I bought it. One of my first
 'modifications back to original' was to make a crude aluminum bracket to
raise the gearbox and spread the load on the tunnel floor. With hindsight, it
seems the vibration is less now, but till present. Did I partly fix the
problem by slightly changing the relative angles of engine and pinion shaft?
Has anyone fussed with this variable? One other detail is that there is a
pronounced angle of the engine/transmission itself--the engine is not parallel
to the centerline of the car... could this be another cause? Input appreciated
as I prepare to pull the engine and will have the opportunity to make
adjustments! Cheers, John Donohoe SimpleSevens