Britishbest Posted January 26, 2016 Report Share Posted January 26, 2016 Hey Guys, I'd like to upgrade to an overdrive. Can anyone help with which overdrive unit works on my 4A solid axle please? Rimmers say I need serial number 22/61712 (same as a TR4?) & IRS cars 22/61753. What are the differences? I also see A types units with serial numbers starting 25, 28 etc. Will any of these fit easily or do I need to just look for 22/61712? Thank you Colt PS - How do you get 'member' against your profile name, mine still doesn't say after 2 months? Quote Link to post Share on other sites
Bob Smith Posted January 26, 2016 Report Share Posted January 26, 2016 Colt, There are 2 distinct types of A Series o/d fitted to TR's. The difference being that the the later version 22/61753 has a cushioned engagement which is essential for all IRS cars. Rimmers are therefore technically correct in saying that you need 22/61712 but there is no reason that a later unit could not be fitted to your solid axle car. Laycock part numbers that start 22 mean a 22% reduction in engine speed; those that start 25 mean 25% reduction and so on. When looking for an o/d that was not originally from a TR there are a number of other considerations not least of which is the rear mounting & position of the overdrive solenoid. So it is probably best to concentrate on TR units though other members have used a variety of units with mods. Quote Link to post Share on other sites
John Morrison Posted January 26, 2016 Report Share Posted January 26, 2016 Answer is any tr overdrive will fit your car, Original is A type and the suffix, eg 22/ is the percentage reduction against non overdrive . Thus any will do but 28/ i.e. 28% is the best. John. Quote Link to post Share on other sites
John Morrison Posted January 26, 2016 Report Share Posted January 26, 2016 Well done Bob, need to type faster! John. Quote Link to post Share on other sites
Britishbest Posted January 26, 2016 Author Report Share Posted January 26, 2016 Awesome replies thanks very much guys. Quote Link to post Share on other sites
The_Doc Posted January 28, 2016 Report Share Posted January 28, 2016 Even though I'm getting on this a bit late, I've also got a solid axle Tr4A that I'm currently doing up. I bought myself a J-type overdrive (25%) and this seems to fit in well. There are some other things you need to consider like the speedo drive but most things are minor issues, so don't let it put you off. Adam Quote Link to post Share on other sites
Britishbest Posted January 28, 2016 Author Report Share Posted January 28, 2016 Was it a straight fit Adam or did it need any mods? Was it from another TR? Quote Link to post Share on other sites
The_Doc Posted February 3, 2016 Report Share Posted February 3, 2016 Sorry for the late reply Colt. I actually bought an old gear box from a dolimite sprint that had a J-type OD on it. I am hoping to just just chuck away the dolimite gearbox and then fit the J-type overdirve stright onto my Tr4 gearbox. After a very quick inspection, I think everything fits, I need to obviously change the main shaft, but this shoudl all be do-able. To get it to fit into the car, you need to mount it correctly and Rimmer do sell a conversion bracket that might help (http://www.rimmerbros.co.uk/Item--i-GRID200129). Other then that things are fairly simple I believe and most problems should have a way around them. Adam Quote Link to post Share on other sites
TR NIALL Posted February 3, 2016 Report Share Posted February 3, 2016 Sorry for the late reply Colt. I actually bought an old gear box from a dolimite sprint that had a J-type OD on it. I am hoping to just just chuck away the dolimite gearbox and then fit the J-type overdirve stright onto my Tr4 gearbox. After a very quick inspection, I think everything fits, I need to obviously change the main shaft, but this shoudl all be do-able. To get it to fit into the car, you need to mount it correctly and Rimmer do sell a conversion bracket that might help (http://www.rimmerbros.co.uk/Item--i-GRID200129). Other then that things are fairly simple I believe and most problems should have a way around them. Adam Adam,please do not Throw Away the Dolly Gearbox,someone will be delighted to take it off of your Hands I'm sure. Quote Link to post Share on other sites
Britishbest Posted February 4, 2016 Author Report Share Posted February 4, 2016 Adam let us know if it fitted without issues. Thanks Quote Link to post Share on other sites
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