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

[John Donohoe]

Hmm, from what I recall (have just kind of gotten used to it over the years)
clutch in has no effect... that isolates engine, but the driveshaft is still
spinning though... I'm wodnering if there is actually something to the
'built-in offset to minimize harmonic vibration' concept?
jd



--- On Thu, 1/7/10, Jim <britbits at netzero.com> wrote:

From: Jim <britbits at netzero.com>
Subject: RE: [Vintage-race] Driveline angles and vibration? (General, but in
my Lotus  Seven)
To: "'John Donohoe'" <sevenamerica at yahoo.com>, lotus at se7ens.net,
vintage-race at autox.team.net
Date: Thursday, January 7, 2010, 1:08 PM

John,

Basic diagnostics?   Is the vibration speed dependent or rpm dependent?

Does it get better or worse going throttle on/throttle off?   Did you try to
push in the clutch or put it in neutral while the vibe is happening?

And what's the condition of the rest of the suspension? 


Cheers,

Jim
Dallas
'76 DM Spitfire autocrosser
'61 Morris Mini vintage racer

-----Original Message-----
From: vintage-race-bounces at autox.team.net
[mailto:vintage-race-bounces at autox.team.net] On Behalf Of John Donohoe
Sent: Thursday, January 07, 2010 10:06 AM
To: lotus at se7ens.net; vintage-race at autox.team.net
Subject: [Vintage-race] Driveline angles and vibration? (General, but in my
Lotus Seven)

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
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