In <m0twLAC-0009oLC@walnut.holli.com>, Robert J. Donahue wrote:
>I've driven several cars that had non-sycromesh gears, usually reverse or
>reverse and first gear. I know the non-syncro gears are noisier (kind of a
>whining sound), but why is syncro considered so desirable? Can anybody
>describe what it is in simple terms?
The best definition I can think of is that you know very quickly when
you don't have it....
When you are in a given gear, you have a fixed ratio between the input
shaft and the output shaft of the tranny, say 3:1 for a lower gear.
If the output shaft is going 200 rpm, then the input shaft (connected
to the engine through the clutch) is going 600 rpm. If you then shift
to a higher gear (that has a lower ratio, say 2:1), the output shaft
is still going at 200 rpm--after all, it's connected to the wheels.
This requires the input shaft to be slowed down to EXACTLY 400 rpm for
the gear you are going into to mesh properly, without clash. That is
the job of the synchromesh mechanism. It adjusts the speed of the
input shaft (while disconnected from the engine via the clutch) to
match what it should be to get clean, clash-free shifting (either up
or down). If you do not have synchromesh, shifting becomes an Art.
Reverse is never synchromesh. All MG trannies except later B's do not
have synchro on 1st gear, requiring either a full stop (which stops
the output shaft) or great care in shifting into first.
A. B. Bonds
|