[TR] TR4 Gearbox ID

[Randall]

> Is there a way to identify if the car has the optional 4.1:1 
> rear axle ratio?

If the factory installed a 4.1 axle, then the calibration number on the
speedometer will be higher than usual; somewhere around 1350 instead of
1150.

But since parts are swapped around so often, the only way to be certain what
is in there now is to check the ratio directly.  One way is to jack up one
rear wheel (leaving the other blocked from turning) and mark the driveshaft.
Now count driveshaft turns while you move the wheel through exactly two
turns.  If the driveshaft turned a bit less than 4 full turns, it's a 3.7.
If it turned a bit more, then it's a 4.1.  You can make the difference more
noticeable by going for more turns of course; 20 full turns on the wheel
should give you either 37 or 41 turns of the driveshaft.

Oddly enough, my previous TR3A was equipped with a 4.1 by the factory (only
car I've ever seen that was) but had a 3.7 when it came to me.  My current
TR3 had a 3.7 installed by the factory (no OD), but had a 4.1 when it came
to me (and still no OD).  My long-range plans are actually to convert it to
3.45 gears (from a Triumph saloon or PI TR6) as the 4.1 gears are a waste
(and the local police tend to frown on spinning the wheels in 1st gear).
With the short, wide tires I use, the 3.45 will give me about the same
effective gearing as the 3.70 and the original tall skinny tires.

Randall