The major advantage of the S3 box is synchromesh on all forward gears compared to only 3 & 4 for the S1,2,2a box. But the later S2a boxes are considered to be both stronger and more durable.
Late S2a and S3 boxes have almost identical gearing and late 2a and S3 transfer cases are essentially identical. During early S2a production ratios were changed slightly in both transfer low range and the indirect gears in the main gearbox (keeping overall gearing in 4H and 1L the same, but all others a bit different), but otherwise ratios remained almost the same for all Series Landrovers.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
Bookmarks