Overdrive numbering

[Peter Douglas Winn]

A new member in the club ask me what the numbering on the overdrive mean? I could not answer this question. All I know is the first 2 numbers reflect the step down ratio. 22/XXXX for an "A" type or 27/XXXX for a Vovlo "J" type. I also know the Laycock provided O/Ds as far back for Standards and Renowns in fact they even supplied American Motors manufacturers. They were widely used in England, Sunbeam, MG, Reliant, Jaguar and Hillman, Ford Anglia 100E. In fact Ferrari , Fiat even Aston Martin and Jenson had O/Ds. I cannot find an explanation of the numbering.

[Mike C]

Buckeye has some details on the A Type numbering. 

http://web.archive.org/web/20040409105558fw_/http://www.buckeyetriumphs.org/technical/AOD/AOD1/AOD1.htm

 

[Peter Douglas Winn]

Mike one can see that the important numbers are 3rd 4th 5th and 6th positions there looks to be a link between these 4 numbers and the individual model and make of car. As an example I have found out that 32/3004 is for a HIllman Minx & Rapier II whereby  32/3017 is for a Hillman Minx Series II.

[Mike C]

You're right, have a look at the extracts from  "Appendix A "of the Laycock manual:

 

 

Laycock OD Applications.pdf

[Peter Douglas Winn]

That's great but what is the system for numbers after these 6 numbers. I have a suspicien that the next 2 numbers are very relevant in identifying which of the cars models are involved. e.g 38 would be an early model TR6 and 76 a late TR6. Then what is a 36?