Re: Bucking in reverse gear

[Scott Fisher <sfisher71@domain.elided>]

--- stephen hood <hoodmeister@domain.elided> wrote:
> Ladies and Gents-
> I have a 67 Duetto that has a peculiar reversing
> problem.  The driveline 
> causes a severe oscillation, or bucking when
> reversing.  I've lived with it 
> for many years and was wondering if anyone had the
> definitive solution to 
> the problem.  I've heard theories and have replaced
> many parts through the 
> years but it still happens.

Betcha somebody put in a later gearbox at some point,
with its later transmission mounting bushing, as this
is exactly what I experienced with the '67 GT Junior I
used to own when I put in a later gearbox.  The
problem: the '67s have a mechanical clutch release,
with a cable that is pulled by a bellcrank when you
press on the pedal.  Pulled tight, the clutch
releases; left slack, the clutch engages.  With the
original gearbox, the bushing was designed to make
this work in both directions.

The problem is that the later gearboxes have a softer
bushing with a different shape, because the later 'box
uses a hydraulic clutch.  Going forwards, this is no
problem, because the rear-wheel torque "does the right
thing," keeping the cable taut when you're on the
pedal.  But going backwards, the rear-wheel torque as
you start to engage the clutch slackens the cable,
which causes a sharp engagement of the clutch -- the
first jerk.  This causes the cable to go taut again,
which makes the car jerk backward, which makes the
cable go slack, which makes the car jerk, which -- and
it keeps up till you put it in neutral.

It *could* also be simply that the transmission mount
has softened to the point that it's not restraining
transmission/engine movement in reverse.  If I recall,
the difference should be visible by crawling partway
under your car -- if the bolt through the rear of the
transmission mount is in the center of the mount, it's
the early style; if it's well toward the bottom of the
mount, it's the later style.

I've heard about good results by slipping a piece of
fuel hose over the transmission mounting bolt and
putting it back in (for the later-gearbox problem). 
This is a lot cheaper than retrofitting the '69-only
floor-mounted hydraulic clutch, though if you do THAT,
it's easier to put in a 2L later... :-)

Best,

--Scott Fisher
  Tualatin, Oregon
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