There are two types of gearboxes on both Unimog 406 and 416:

F type and G type.

There are numerous improvements that were phased in at various times (improved splitter gear, improved transmission lubrication, improved venting, changed teeth count of PTO drive and driven gears, etc..

From start of production up until transmission no. -010398 (Chassis no. -009058), approximately August 1968, you have the "F" transmission. This does use a different rear torque tube and driveline.

From transmission number -010399 to -056864 (Chassis No.(s) -009059 to -028718) approximately November 1976, you have the "G" series transmission, with the improved housing. (Transmission model 717.800)

From transmission number -056865 (Chassis No. -028719) approximately January 1977 you have the "G" transmission. (Transmission model 717.801)

And I want to add that info I get it from Eric van Mierlo of VAM PARTS:

"All F and G types gearboxes are synchronised, and they share all the same synchroniser rings as the older 404 / 411 transmission (only the 5 gear ring is replaced later by a steel version because of too much wear)."
 

Unimog 406 & 416	Date	Chassis number	Transmission number	Transmission serie	Transmission type
	1963 > August 1968	0 > -009058	0 > -010398	UG 2/27	F
	August 1968 > November 1976	-009059 > -028718	-010399 > -056864	UG 2/27	G 717.800
	January 1977 >	-028719 >	-056865 >	UG 2/27	G 717.801

Is it a ''F'' or ''G'' gearbox?

The characteristic of the F type is a small lid in the direction of travel on the right, at the point where the strap offset was on the U 401. The G type transmission has no lid there.

The G gearbox can be identified externally by the presence of a raised casting on the passenger side of the gearbox that looks like a pentagon with unequal sides.

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox

Unimog F type gearbox

Unimog G type gearbox