Matt Whiting wrote:



I've not seen this before. This may be true for passenger cars, but for
pickup trucks, OTR trucks, off-road equipment, etc., each gear is
equally likely to be used and typically full throttle is more likely to
be used in the lower gears. I've never heard of any of the gears being
designed for "light" usage in any manual trans with which I'm familiar,
but I'm not that familiar with pax car manuals.

It used to be that 4th gear in most four-speeds was 1:1 and this was
often accomplished by simply connecting the input and output shafts
directly with a collar. So, I suppose this could have been more rugged
as the gears were just along for the ride at that point. However, some
new transmissions have the 5th or 6th gear as a overdrive gear, and
occasionally even the 4th, and may not even have a 1:1 ratio. In these
designs, every speed is being driven through the gear set/layshaft.

If you have a design reference for transmissions being designed to not
handle full torque in anything but high gear, I'd be interested in
seeing it. Also, if you have a list of such transmissions that would be
interesting as well.

Matt

I would think that if anything the lower gears would have to be be
beefier than the higher ones, at least on the output shaft. Torque
increases as rotational speed decreases, right? This is why axle shafts
tend to snap when starting a heavy load from a dead stop.
I just replaced fifth gear in my Nissan NX a month or two ago. It was
pretty much worn out, and not really beefy to begin with. You do spend
most of your time driving sitting in your highest gear so it will see
the most wear, but not necessarily the highest torque loads. All the
gears are equally wimpy, but the 1st and 2nd shifting collar is a little
longer and engages more teeth than the others. This seems to confirm
that 1st and 2nd are stronger gears than 4th or 5th.This car has the
smallest tranny I've ever worked on and one look inside would make you
REALLY glad you aren't flying behind it. Those gears are tiny, and
eyeball engineering would lead me to believe they aren't up to the job
of swinging a prop. Graham's two failures pretty much confirm this. I
can't imagine the mazda's gearbox is any beefier than this one. Flying
with one of these is 'experimental' all right.

Jason
Challenger-II