A new Triumph designed Five-speed gearbox was also developed for the SD1 – which was proposed at the time to
be first of a family of new gearboxes for use across the Leyland range. The SD1 version was called the LT77 gearbox in-house (because
the shaft centre dimension was 77mm) and was first shown in the TR7 rally car, a few months before the launch of the SD1. The design
of this gearbox was modular, in as much as different versions of this gearbox could be used for different applications. As it happens,
Jaguar was a recipient of this ‘box for the XJ6 4.2 in 1979, but the proposed 66mm version that was to appear in the ADO77 and
the SD2 never materialised when it became clear that the money had run out to produce these cars.
In terms of suspension for the SD1, there was a departure in store: Whereas the P6 used DeDion rear suspension to great effect,
this system was rejected for the SD1 on the grounds of cost and complexity. King maintained that a live rear axle (in this case,
a torque-tube type design) would be able to do the job equally as well as any of the esoteric independent systems used in the
SD1’s rivals. Careful location and development, concentrated on the bushing for the rear axle were incorporated at the rear
– and at the front, industry-standard McPherson struts were employed, as opposed to the horizontal coils used in its predecessor.
This may have seen like a retrograde step in terms of technology, but Spen King considered the McPherson strut arrangement to be far
less liable to suffer from the effects of camber changes than the double wishbone arrangement in the P6 and, therefore, a more stable
solution in emergency manoeuvres.
One major advance for Rover was the adoption of the Burmann Power assisted steering system for the SD1. This was a conventional PAS
system, but unlike others of the time, which traditionally retained standard gearing, the advantage of power assistance was put to great
use. King decided that much higher gearing could be used than standard, so the SD1 ended-up with gearing equating to 2.7 turns of
the wheel from lock to lock. At this point in time, only Citroën with their Diravi system had engineered Power steering to be so
directly geared. Development engineers loved this system and it was noted that unlike the Citroen set-up, people new to the SD1 needed
much less acclimatisation drive the Rover, although the “sneeze factor” was still somewhat overwhelming for some. It was
very conventional it its feel, even though its directness and, therefore, responsiveness were vastly better than its rivals could offer.