overdrive units

Can anyone point me in the right direction for a web site that explains
how an overdrive unit works with the transfer case. I am having trouble
understanding how switching one extra gear in or out of the transfer
box (say an LT230) alters the ratios.

Thanks
Smokeyone

[email protected] wrote:

> Can anyone point me in the right direction for a web site that explains
> how an overdrive unit works with the transfer case. I am having trouble
> understanding how switching one extra gear in or out of the transfer
> box (say an LT230) alters the ratios.
>
> Thanks
> Smokeyone

Try www.faireyoverdrive.com/fairey1.htm

The overdrive unit does not consist of one gear - it is a two speed (direct
and step-up) gearbox that mounts on the PTO location of the transfer box
and replaces the gear on the back of the gearbox main shaft. It has
concentric input and output shafts, and in direct they are locked together
so that it just behaves as if the original gear were there. In overdrive
the gearbox main shaft drives a step up gear set - actually four gears, one
on the input shaft, two on a layshaft, and one on the concentric output
shaft, so that the first gear in the transfer case is now going faster than
the gearbox main shaft.
Hope this helps - the description is actually for a Series Landrover
overdrive, but the RR/90/110 works exactly the same way.
JD