Marcin Posted March 8, 2013 Report Share Posted March 8, 2013 (edited) I'm going to attend TR international this year and facing long motorway driving ( 2200 km and back). I'm considering the overdrive conversion of my TR3A (number TS75769L). I have following questions: What type of overdrive should I look for? J or A?? Which gear ratio? Is it necessary to exchange my whole gearbox or its possible to convert original one? What associated parts need to be replaced (driveshaft, wires)? Any recommended source of parts for this conversion? Any other suggestion related???? I'll appreciate any help in that matter. Marcin Warsaw, Poland Edited March 8, 2013 by Marcin Quote Link to post Share on other sites
John390 Posted March 8, 2013 Report Share Posted March 8, 2013 (edited) There has been a lot of talk about this on here. Go to the search box at the top right and put 'overdrive conversion' (forums) Loads of stuff! Cheers John Edited March 8, 2013 by John390 Quote Link to post Share on other sites
Kiwifrog Posted March 8, 2013 Report Share Posted March 8, 2013 (edited) Marcin The ideal is an A type overdrive gearbox from a TR, Mechanically its a bolt on affair and of course there are the eletrics to modify. It uses the same driveshaft. Adding an overdrive to an existing non OD box requires the gearbox mainshaft to be changed as well as sourcing the overdrive mounting plate etc. Another option is a saloon type box either A type or J type but the modifications are more involved Regards Alan Edited March 8, 2013 by Kiwifrog Quote Link to post Share on other sites
vivdownunder Posted March 8, 2013 Report Share Posted March 8, 2013 Yes, A type but they are getting scarce. The correct model was 22/61374 but you can fit 22/61712 from a late TR4 and the softer engagement 22/61753 used on IRS cars. Other O/D's may not have the correct speedo drive. J Types can be adpated to fit, but need a special rear mount. TR3A ratio in top overdrive was 0.82 with 3.7:1 diff. Can convert the original gearbox. Associated parts needed are a gearbox mainshaft for O/D, gearbox end adaptor, O/D relay, O/D wiring looms, O/D toggle switch. LHD cars with O/D used a longer speedo cable. Driveshaft doesn't change. An O/D and related parts might be easier to find in the UK from a supplier such as Classic Gearbox Repairs, but there are others. Other suggestions - don't just purchase an O/D and fit it without having it fully checked over by an expert. Usually they have been removed from a car for a reason. Best to fit a new operating solenoid too. After fitting an O/D, synthetic gearbox oil can't be used. There are many opinions on the best oil to use, but ordinary SAE 30 non detergent oil was used originally.. Make sure the O/D has a set of 3 pickup magnets inside the large drain plug to catch any floating particles. When filling the gearbox, run it for a short while to get the oil through to the O/D, then top up. Viv. Quote Link to post Share on other sites
johnhodges Posted March 8, 2013 Report Share Posted March 8, 2013 Marcin I have sent you a PM John Quote Link to post Share on other sites
AlanT Posted March 8, 2013 Report Share Posted March 8, 2013 This is a very helpful company: http://www.overdrive-repairs.co.uk/ Al. Quote Link to post Share on other sites
Marcin Posted March 9, 2013 Author Report Share Posted March 9, 2013 (edited) Thank you all for your input. Johnhodges I have sent an email. If I go with J type overdrive, what modification have to be done. There is Overdrive Conversion Mounting Bracket available at Moss. Any other large modification required???? What could I expect in terms of driving performance difference if I go with J type instead of A??? Regards Marcin Edited March 10, 2013 by Marcin Quote Link to post Share on other sites
Richardtr3a Posted March 9, 2013 Report Share Posted March 9, 2013 Overdrive Repairs Services in Sheffield repiared my overdrive gear box after ten years of aggravation from other suppliers. Stick with ORS they are vey experienced.. It makes the car very smooth on motorways and helps alot with fuel consumption as well. A good investment. Quote Link to post Share on other sites
Ashley James Posted March 9, 2013 Report Share Posted March 9, 2013 It's very handy having overdrive on second for blatting past self righteous ditherers that clutter almost everywhere these days. Quote Link to post Share on other sites
AlanT Posted March 9, 2013 Report Share Posted March 9, 2013 J type has a better solenoid arrangement. This is a weak point on A-types. J type has a softer engagement. The early A-type has a huge piston and engages with a bit of a jump. Al. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted March 9, 2013 Report Share Posted March 9, 2013 I would have thought a cheaper option is to convert the rear axle ratio from the standard 3.7 to the TR6 3.45.this gives almost 2 mph or 3 kph increase in road speed per 1000 rpm 3000 rpm gives 98 kph standard as against 106 kph with the 3.45 TR6 axle ratio. According to the excellent minty lamb calculator. http://www.mintylamb.co.uk/gearspeed/ Overdrive gives a larger engine rpm drop for given road speed but costs an arm and a leg to do it as original. Remembering this is a 3 synchro box that is being proposed by Marcin as a starting point. Discuss........ Peter W Quote Link to post Share on other sites
AlanT Posted March 9, 2013 Report Share Posted March 9, 2013 Actually I nearly told him not to bother because OD's are a pain in the neck. Even though I have one and enjoyed dismantling and fixing it. Thats the point really. Its an interesting dinosaur. A blind alley in vehicle development. Cheaper more reliable ways to do the same thing. Just think about it. A miniaturised epicyclic gbox. 400psi hydraulic pistons. Oil-pump and relief-valve. Rising-roller uni-clutch. Friction cone-clutch. Ball sealed operating valve. High current linear actuator with cut-out. How many more maintenance problems can you put in one thing that does not do much. The good feature is that the most likely failures still leave direct drive working. If I was planning to drive 2000km through half a dozen different countries, in a 60 year old vehicle .... Al. Quote Link to post Share on other sites
Guest ntc Posted March 9, 2013 Report Share Posted March 9, 2013 Triumph must have got it wrong then they built high reving engines Quote Link to post Share on other sites
johnhodges Posted March 9, 2013 Report Share Posted March 9, 2013 Al and Peter I think you were a bit harsh on overdrives. One of the beauties of driving 50s and 60s classic of all makes is the ability to gain or lose 500rpm at a flick of the overdrive switch, in 3 gears in the sidescreen cars. I always found them to be one of the more robust components, as you say if it does fail to engage you've still got direct drive. I wouldn't consider not fitting one to any car which didn't have one if only for the fun aspect. Who wants to be stuck with a fixed higher ratio back axle, especially for the average non motorway driving conditions where nippiness is more important than high speeds. John Quote Link to post Share on other sites
Ashley James Posted March 9, 2013 Report Share Posted March 9, 2013 I've got and overdrive, a 3.5 to 1 axle and a sports cam. All works fine and means 84 mph should be 3000 revs, but neither dial supports that theory. I'm in a very hilly area with no issues. Even with overdrive, TRs are undergeared by today's standards. Quote Link to post Share on other sites
AlanT Posted March 9, 2013 Report Share Posted March 9, 2013 (edited) Oh I didn't say it wasn't a useful or fun thing to have. Just that there are a lot of bits to go wrong. If you strip one you realise that it was a struggle to get it into the short length available and some of the bits would do with being thicker. I'd recommend that Marcin reads: http://www.buckeyetriumphs.org/technical/AOD/AOD2/AOD2.htm and its companion articles. These are beautifully written by a top mech-engineer. I too had "broken bits" inside. In my case the end had come off the circlip. Fortunately it made its way to the bottom without meeting any gear teeth, just leaving a few "dings" here and there. Al. Edited March 9, 2013 by AlanT Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.