Moderator

Gearboxes and rear differential codes are made up as follows

After the letters I.E. 4Z, AOK, ASU etc there is a 5 figure nr, as in 4Zxxxxx or ASUxxxxx

this can be broken down to by reading the first two numbers = date, second two = month, fifth = year

so 4Z 25117 is a 4Z gearbox made on the 25-11-(198)7,
or ASU05049 is 05-04-(198)9
or ATZ11111 which was made on 11-11-1991

btw the changeover number (Date) for the Rallye gearbox from non oilway to oilways is ASU29059 29-05-(8)9 being the first with oilways