Overdrive on AC Moss Box

[DHAceca]

Hi, I need some help, I am looking to convert my AC engine Aceca to run an Overdrive gearbox. From my research this was a factory option on the AC engine cars, again from what I understand the Moss box is suitable to accept an A Type overdrive using an adaptor plate. Firstly would this have been the factory fit overdrive (Laycock A Type)? I ask as from looking at A Types they are bulky and would require the widest point of the tunnel to be increased in length considerably as well as the moving of the cross member back. This just seams a lot of modification for something on a factory options list even on a hand built car. Or was overdrive only fitted using the AC Lightweight gearbox?
   Any information or pictures of an AC gearbox with overdrive would help me greatly to understand how this was done and confirm I am heading down the correct path. Many thanks David

[Klassik Metall]

Hello David,
   
   The A type was the only Laycock unit available until 1959 and therefore was the type fitted in the Aceca. It was also matched to a very similar type Moss gearbox in several Jaguar models.
   The A type is big bulky and  quite heavy when compared to the later units but I don't think that the repositioning of the gearbox xmember would have caused AC too many headaches as
   it was in slightly different positions for each engine variant anyway.
   
   In Acecas fitted with an overdrive the standard fiberglass tunnel was split and lengthened with an aluminium centre section, see photo below.
   Regards Luke.
   

[Robin A Woolmer]

Gerry Hawkridge has a Jag MK2 moss gearbox with overdrive he might sell you, I have fitted a T5 Tremec on an AC engine for an Ace owner, much lighter than a Moss!I realise it is none standard!
   
   Robin

[Jam2]

Robin,
   The T5 Tremec seems to have a huge 'uplift' in ration from 4th to 5th,  0.63.  did you need to lower the axle ratio or was it satisfactory? (or was I looking at the wrong spec!)
   John.

[Robin A Woolmer]

The fifth gear was 0.85 so not a bad step up, also the engine will rev comfortably up to 6,000 with a good torque curve from below 2,000 to 5,500!
   
   Robin

[DHAceca]

Great thank you all for the help and advice.  A  photo of the chassis mount/modification would be great if anyone has one.

[Robin A Woolmer]

You should be aware that Tremec Box conversions are available for Jaguars which fit the Moss Type Bell Housings so potentially could be adapted to use with the AC Engine, you may know that the gearbox input shaft must be modified with a bush to accept the AC Crankshaft Spigot!
   
   Robin