[TR] How do they manufacture gears?

[Karl Vacek]

Never machined a TR gear, but mainshafts were case hardened.  When my '71 
TR6 ate its overdrive at about 24,000 miles (in 1972) I bought a '64 OD 
transmission for parts.  Everything in the OD fit fine, except the nose of 
the mainshaft was too large to fit into the beefier TR6 pilot bearing in the 
back of the input gear.  Being a Saturday, and not wishing to wait to order 
(or pay for) a brand new mainshaft, I tried turning down the '64 mainshaft. 
A carbide tool did a great job and left a decent finish.  When I was done, I 
could see a color and finish difference where I'd cut through some of the 
case hardening into the softer steel beneath.  That worried me for a while, 
till I looked at the nose of the original part (I'd bought this car new and 
the transmission had never been touched before), and saw the same pattern, 
as if it had been cut in the same way.  I wondered then and still if Triumph 
hadn't cut down some earlier mainshafts for later production.

Karl

PS - It worked fine for another 12,000 miles, till I sold the car.



>> Then they
>> are case hardened to resist wear withoug becoming too
>> brittle.
>
> I've been wondering about that.  Some simple experiments with original
> Triumph gears seem to indicate that they are not case hardened.  In fact,
> they aren't very hard at all.  Compared to say, a cheap socket, they cut
> quite easily.  So I would guess that they are only heat treated and left 
> at
> a moderate temper.
>
> Randall