I have been building race close ratio boxes for these cars for 30 years.
The overdrive rarely gives problems if built properly, but it benefit :
weight ratio is always a factor. To stop cluster shaft problems, we use
taper roller bearings in both the big box (TR etc) and the medium box
(GT6/Vitesse/Spit 1500). This is a major conversion, but solves problems
forever.
With respect to ratios, it is easy to get some useless gears if the
wrong combination of overdrive ratio and gear ratios are used. Most of
our race TR's use the Leyland ST gear set (made for the dolomite
Sprints) plus a J type overdrive of 0.8 ratio. This gives a very useful
3rd overdrive that is great on twisty circuits. We get the overdrive
working faster than a driver could ever change a syncronised TR box.
If anyone wants to send me their gearbox gear counts, overdrive ratio
etc, I'll send back a gear ratio chart for them
Terry O'Beirne
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