🚀 go-pugleaf

	Volvos have had the electric overdrive available since at least
1967 on most models, and standard on up-market models since 1970 (or so)
. I have a 1971 142E with OD and the standard (for this model) 4.31
final drive ratio. This makes for  pretty speedy progress through the
gears, and it would be revving far higher than appropriate for cruising
if it did not have the OD . The OD has a ratio of 0.79 to one, so
when engaged, the final ratio "appears" to be about 3.44 to one.
The non-OD Volvos of this era had 4.10 to one ratios, eventually falling
to about 3.77 with more recent years. I believe the early gearboxes
(M41's) also had longer indirect gear ratios, making them more of
a "close-ratio" box (its all a matter of degree). 
	My 142E definitely gets better hwy mileage than other 140's
without OD, but I suggest it is largely due to the fuel injection
, rather than the OD. If my diff ever blows up , (162,000MI now) I
will replace it with a 4.10 to one unit, 'cause I think it has the
torque to twist it. With the OD engaged that will yield an
effective overall ratio of about 3.24 to one, for less noise
and wear.
	I think the main reason for Volvo doing this ,
(using separate OD's) is to avoid designing, and tooling a new
(5 spd) transmission. 
	The Overdive units are made by Laycock , in England (HORRORS!)
Guess what is the only part of my Volvo that has ever leaked oil 
(no prizes)