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Which overdrive is stronger A type or J type in a Stag

Martins Stag

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I always thought that the latter J type gearbox and overdrive in the Stag was the strongest, but talking to "gearbox Pete" who rebuild it he says that the parts in in are bigger in an A type rather than a J type which was interesting. So does this mean that BL went to the J type overdrive to standise on an overdrive type  to reduce cost or is there a way the J type is stronger that the A type? 

If the A type is stronger  is it worth changing my J type out  and is it very involved? 


Answers on a postcard please? 



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I'm fairly sure the J-type was commonisation and cost reduction. The A-type is a big, beefy unit. On the smaller cars, the D-type is definitely weaker than the J-type but I suspect the A-type is the strongest. That said, the main issue isn't really the mechanical bits but the clutch pressure. The J-type does have a very efficient hydraulic system so it may have a higher torque limit than the A-type because of that.

All of which is long-hand for "urrr I dunno"

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I too can't get my head round it either, but it was mentioned number of time on the old old CT forum.

There is one thing I have noticed, my J-type equipped cars seem to upset the synchro on 3rd if I forget to disengage it, where as the A-type and D-type ones don't. 

Seems to imply more rotating mass. 


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4 hours ago, thescrapman said:

mentioned number of time on the old old CT forum

To whom it may concern... just imported 144 "overdrive" related conversations (about 4k posts) from the old site at around lunchtime, so you might be able to find something useful now in them via the search 👍 

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The old adage "if it ain't broke, don't try to fix it" springs to mind!  

Both Stag boxes are strong, and Stags don't tend to eat them as long as oil levels are checked regularly and changed periodically. 

If you have a problem then like for like is the cheapest and easiest solution.  To convert a box from J type to A type involves a fair bit more than just swapping an overdrive unit.  I'm pretty sure the gearbox mainshafts will be different, then there will be the solonoids, adaptor plate, wiring looms and possibly even rear mountings or crossmember - tbh I can't remember the detail nowadays. 

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I was always advised the J-type was a stronger unit, compared to the A-type O/D unit.

If you have a standard engine, and don't drive particularly hard, either will be more than adequate.  I have an A-Type Stag derived gearbox in my TR6, with competition O/D unit, and it is more than capable of absorbing the power.



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