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Triumph Repair/Triumph differentials


Bobbyspit wrote at 2010-02-04 22:18:50
You could fit a different Differential from a triumph, GT6 has a differential that is a lot higher but this will mess up your gearing in other ways. Do as Howard says and fit an overdrive box. They were an add on for the Triumph owner to use motorways (freeways) at lower revs,


BRG wrote at 2013-08-14 01:19:38
Actually, the GT6 or 3.27:1 differential was fitted to the 1980 Spitfires sold in Switzerland. It is more reliable and trouble free than any problematic electronic overdrive. In my opinion, there is no real problem, especially if you fit your Spitfire with originally designed and fitted dual 1.5" SU carbs that can be purchased on ebay UK with the correct intake manifold, rebuilt, and make a world of difference. The GT6 3.27 differential is a simple swap and will reduce your rpm's by about 600 at highway speeds.  The difference per 1000 rpm's is 20 mph vs. 17 mph, so at 60 mph your rpm's would be 3000 with the 3.27, and over 3500 with the 3.89. At 70 mph your rpm's would be 3500 with the 3.27 vs. over 4100 with the 3.89.

76 Spit wrote at 2014-06-23 02:01:49
BRG is correct.  I set up my 1500 with rebuilt dual 1.5" SU carbs and correct intake manifold from ebay uk, and then swapped the 3.27 GT6 differential. Overall, no appreciable loss in the low gears, and revs a lot less at highway speeds.  Don't waste time and money on the electronic overdrive or with the 5 speed Ford Mercury tranny available at about $3800 with tax and shipping, and an expensive installation.  

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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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ASE Master Auto with L-1 certification up to 2000

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