> Calling all gearbox gurus... I have a UK supplier for a TR4
> close-ratio gearbox gearset. They're helical-cut gears, work with
> ordinary synchros, etc, and they're not expensive
>
> I think that means the "close-ratio gearset" is made up of easily
> available bits from other boxes
>
> So, any ideas what?
I'm not sure where yours is from, but there are several close ratio gearsets
listed in the Moss UK TriumphTune catalog, one of them is only 75GBP in my
2002 catalog. ISTR hearing these were factory parts for the Dolly Sprint,
but I don't know any details, except the Dolly clutch plate has to be used
as the input shaft is a different size.
> The ideal would be a slightly lower third and
> fourth, I think, if I keep the OD
4th pretty much has to be direct unless you completely redesign the gearbox.
There are no actual gears for it, the shift hub just locks the input shaft
to the output shaft.
So, the usual way to get "close ratio" is to move 1st & 2nd up closer to
3rd. If 1st or 4th is too tall, then you lower the final drive ratio
(numerically higher, like 4.1:1).
> On the subject of overdrives, has anyone tried changing the OD
> ratio? 3rd over is just 4% different to 4th, if I remember the
> ratios correctly. If we make the gap between 2nd & 3rd (and 3rd &
> 4th) closer, then the overdrive won't sit between the gears - 3rd
> over will likely be taller than 4th!
>
> Ideally we'd use the OD to split the gaps exactly between gears -
> so we'd need a lower step-up in the OD
The whole idea of 'close-ratio' is to eliminate the need to split, IMO. If
you have an A-type OD, and use 2nd OD, you've already got a close-ratio,
6-speed gearbox ! (3rd OD is not useful as a separate ratio, but can be
very handy at times when you don't want to shift back & forth, like on
twisty mountain roads.)
The TT catalog actually lists a "wide ratio" gearset, to be used in
conjunction with the A-type OD to give 7 useful ratios. Unfortunately, it
appears to be NLA.
Randall - not a gearbox guru but I play one on occasion <g>
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