Identifying Austin Seven Gearboxes
SYN, 2SYN or 3SYN?

The first gearboxes fitted to Austin Sevens were 3-speed crash boxes.  Synchromesh on 3rd and 4th gears was introduced on August 22 1933.  Synchromesh on 2nd gear was added to some models in July 1934.

Chummy 3sp 1Layout Chummy

The gearbox fitted to the early Sevens has a 3-speed crash box with gate change
and layout with 1st and reverse gears to the right.

BH116 1Layout BH116

The early gate change was succeeded by a gearbox with a ball
change having 1st and reverse gears to the left.

BH130 3sp 1Layout BH130

The next gearbox has the 'reversed' layout.


4 sp crash 1Layout 4sp crash




The first 4-speed twin-top constant mesh gearbox, ie crash box, introduced in September 1932 has a large nut at the front end of the cover (arrowed).









From August 1933 the cover has the letters SYN to indicate that the gearbox has synchromesh on 3rd and 4th gears.







2 SYN 1


When synchromesh on 2nd gear was introduced in July 1934 for high-frame models, including sports, but not the van and low-frame chassis, the mark became 2SYN.  '2' indicates synchromesh on 2nd gear in addition to synchromesh on 3rd and 4th gears.






2SYN synchro


As the cover for SYN and 2SYN are interchangeable it is essential that the internal configuration of the gearbox is checked.  The 2SYN gearbox has 3 brass synchromesh rings, the 2nd gear ring is at the rear end of the gearbox.









For a long-time some 'Seveners' have believed that 2SYN indicates 'top-two', ie synchromesh on 3rd and 4th gears, and that 3SYN means that the gearbox has synchromesh on 2nd, 3rd and 4th gears.  This is incorrect because '3SYN' marking does not exist.


This article was written by Doug Castle and Andrew Jarmin, July 2020, to clear any confusion about the identification of gearboxes after a question via our website.


See also:

Austin Seven Gearbox Overhaul

Overhauling the Gearbox

Replacing a 3-speed Gearbox with a 4-speed

Synchromesh Gears