Martins Stag Posted July 22, 2021 Share Posted July 22, 2021 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? Martin Quote Link to comment Share on other sites More sharing options...
RobPearce Posted July 22, 2021 Share Posted July 22, 2021 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" 1 Quote Link to comment Share on other sites More sharing options...
Tim Bancroft Posted July 22, 2021 Share Posted July 22, 2021 Martin, I would tend to agree with Rob, most of the TR Rally boys use A type overdrives, so strength must be the reason. Quote Link to comment Share on other sites More sharing options...
thescrapman Posted July 22, 2021 Share Posted July 22, 2021 I am sure I was told there is more losses in a J- type due to the way it works, compared to D-type. A-type is just a big d-type isn't it? might be rubbish of course. Quote Link to comment Share on other sites More sharing options...
RobPearce Posted July 23, 2021 Share Posted July 23, 2021 9 hours ago, thescrapman said: there is more losses in a J- type Oh? Tell us more! Mechanically they're pretty similar and I don't think the hydraulic system is all that significant. Quote Link to comment Share on other sites More sharing options...
thescrapman Posted July 23, 2021 Share Posted July 23, 2021 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. Quote Link to comment Share on other sites More sharing options...
Ben Hutchings Posted July 23, 2021 Share Posted July 23, 2021 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 👍 1 Quote Link to comment Share on other sites More sharing options...
Martins Stag Posted July 23, 2021 Author Share Posted July 23, 2021 Gents interesting comments! Perhaps i ought to upgrade my Stag by going to a A type overdrive...? Martin Quote Link to comment Share on other sites More sharing options...
mikeyb Posted July 23, 2021 Share Posted July 23, 2021 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. Quote Link to comment Share on other sites More sharing options...
TRTOM2498 Posted July 26, 2021 Share Posted July 26, 2021 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. Cheers. Quote Link to comment Share on other sites More sharing options...
Martins Stag Posted August 11, 2021 Author Share Posted August 11, 2021 Thanks for you inputs. I have a J type that needs 3rd gear syncro replaceing and i have a rebuilt A type gearbox and overdrive. So I was just thinking when I have the gearbox out, is it worth swapping to an A type... I'll have think about it. Many thanks Martin Quote Link to comment Share on other sites More sharing options...
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