<VV> Re: 4 spd syn oil 2-3rd gear

[Jim Simpson]

Hi Chuck.  Not sure if I can really give you any good answers, but I've 
just been all through a late 4-speed and have learned more than I really 
wanted to know about it.

The synchros on all four forward gears are identical in design.  The only 
reason I can come up with for it being harder to shift into lower gears is 
that you are dealing with more rotating moment of inertia with the lower 
gears.  Keep in mind that all the gears are constantly meshed, only the 
synchronizers hubs are moved to engage a gear.  When you shift gears, one 
of the two synchronizer assemblies is moved forward or aft to speed up or 
slow down the INPUT rotating mass to match the OUTPUT shaft.  (The output 
is always hooked to the rear wheels via the differential and is spinning at 
whatever the car speed dictates.)

That input rotating mass includes all of the mainshaft gears, the 
countershaft, the input shaft, and the clutch disk.  When you go for a 
lower gear, you have to accelerate all of this a higher speed than with a 
higher gear.  When the transmission is cold, the oil slows things down very 
quickly, probably to about standstill even on a normal shift.  So 1st to 
2nd with a cold transmission requires spinning everything up to about twice 
as fast (2.20:1 2nd gear) than a 1st to 3rd shift (1.47:1 ratio in 
3rd).  That's twice the amount of energy needed, plus you have all the drag 
of the cold transmission oil on everything.

Once things warm up, at least the drag of the transmission oil is greatly 
reduced.  This would argue that synthetic lubricants with their better low 
temperature flow characteristics would allow easier cold shifts.  But I 
don't know how super slippery lubricants affect the "drag" needed by the 
synchronizers to do the speed matching.

I suppose if you could do a very well timed shift from 1st to 2nd on a cold 
transmission you might find it easy as you caught the rotating mass 
spinning down, but I think that would be very quick shift indeed and the 
cold transmission oil would keep that syncho assembly from moving easily.

Anyway, that's my theory and I'm sticking with it unless someone comes up 
with something more plausible.

Jim Simpson, Group Corvair, '66 Corsa turbo 4-speed.