Re: am i hurting my gearbox?

"RogerM" <RogerM@[EMAIL PROTECTED]
> wrote in message 
news:13qfhj3na5akdad@[EMAIL PROTECTED]
> I understand that. I actually meant matching the revs as sure as ****
(as 
> you accurately mentioned) the grinding of the cones would occur if you 
> didn't. I guess from many years of driving semis back in the 70's and
80's 
> I learnt how to do it and I still do it occasionally (when down****fting)

> in cars.

Large trucks are different (at least most American ones anyway) in that
they 
use a direct mesh trans. The popular Road Ranger is a good example. Every 
gear is a "crash" gear with no synchronizing ability of any kind. The
gears 
have rounded shoulder teeth to help with the engagement, and as long as 
you've got the rpm within cooee of where it's supposed to be the gears
will 
just about fall in (unless of course you're talking about oddball things 
like 13 speeds that have a split on the high ratio gears, as they're
famous 
for getting a bunch of false neutrals).

With a synchro box each gear has a bevelled running face that the synchro 
cone grabs on to and acts like a "brake". As the lever is pulled into a 
gear, the cone seats itself onto the bevelled edge and "brakes" the gear 
(either by slowing it down or speeding it up) so it's speed is matched to 
that of the synchro hub and the spines can engage without crunching the
crap 
out of themselves.

Without using the clutch, the synchro isn't capable of speed matching the 
mainshaft as the engine has control of it, and all you'll achieve by
trying 
is wearing the crap out of the cones in a big hurry.

--
Regards,
Noddy.