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TR2/3/3A Help me understand TR3 synchros

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Lukens

Lukens

Jedi Warrior
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Will someone please hammer the answer to this question through my thick skull?
I've been learning all I can about my TR3 tranny in advance to replacing the synchros.
I understand how the sleeve (collar) rides on the hub, which is splined to the mainshaft. I understand that the synchro is captive on the hub by it's three ears. I understand that the internal taper of the synchro comes in contact with the cone on the speed gear and syncronizes the two. Then I understand that the teeth on the collar mesh with those on the speed gear. The leading edge of these teeth (on both parts) are tapered so they align when brought together. (I assume the connection at the cone slips enough for some rotation between the two).

Why does the synchro ring have the matching "teeth" on it's OD. Wouldn't snchronizing take place without these?
I lose sleep trying to understand this. Maybe when I tear mine down it will make sense.

TIA
Russ
 
Hi Russ,
When you get it apart it'll all come clear. But the long and short of it is you (the manufacturer) only want to have to machine one 'accurate' surface. The cone surfaces next to the dog teeth on the gear and the matching brass 'serrated' surface on the synchro ring. The three ears on the ring could be enough to work well if the tolerances were closer, but with this design the outer dog teeth are needed on the synchro help line things up better. That is they get the cone surfaces facing each in their respective parallel planes. One other thing I'll mention to help with smoother first gear shifts. After coming to a stop lightly pull back into 2nd. Just enough to engage that synchro, which then slows down or stops everything from rotating long enough to make a smoother engagement.
Tom Lains
 
Those brass teeth bind on the sleeve teeth as long as the gears are not at matching speed and you are trying to shove them together. When the speeds match, it relieves that bind, allowing the teeth to slide past each other to engage the steel teeth.

So the brass teeth are what serve to force the brass ring onto the steel cone. The keys (or "ears") don't have enough strength to do that alone. They really only serve to center the shift sleeve and keep the brass rings turning at the same speed as the sleeve. Without driving the ring onto the cone, the gears will never match speeds.

So simple that it seems complicated!

I'm back home with a real keypad, so, here's the corrollary: If the ridges on the brass ring become worn/warped/contaminated, so they do not grab the cone tightly, the brass teeth never feel any bind from the difference in speeds. So the sleeve teeth pass easily over the brass teeth before the gears are the same speed. The result is the familiar grind as the steel teeth scrape at different speeds.
 
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