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I need a little help here. I am in the process of restoring a 1966 Spitfire Mk2, more rust then metal at this point. The car has the original 4 speed trans. My question is will a later trans from a Mk3, 4, or 1500 fit? I would like to upgrade to one of these with O/D.
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Spitfire Spitfire Transmission Swap
- Thread starter JKB1957
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The Mk3 gearbox is identical in every way to the original Mk2 gearbox. A MkIV gearbox is almost identical, save for a synchro first gear and about 5/8" additional length. The non-OD version will still bolt right into your car, since there should be enough travel in the sliding part of the propeller shaft to allow for that length. A 1975 and later 1500 gearbox still will bolt in, but it will require a change of the clutch driven (friction) disc, since the splines are different.
If you add OD to the mix, the above still pretty much applies regarding bolting to the engine back plate. However, the OD gearbox requires a different, special rear mount. Good news is that this mount will bolt up to your chassis without any modifications needed. Some minor sheet metal work may be needed on the driveshaft tunnel area to accommodate the OD gearbox, and a few other fiddly bits are needed.
If you add OD to the mix, the above still pretty much applies regarding bolting to the engine back plate. However, the OD gearbox requires a different, special rear mount. Good news is that this mount will bolt up to your chassis without any modifications needed. Some minor sheet metal work may be needed on the driveshaft tunnel area to accommodate the OD gearbox, and a few other fiddly bits are needed.
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Another and likely much cheaper alternative is to switch differentials. In the US market, all MkIV and 1500 models (except the 1972 model year) had 3.89:1 diffs. later home market-spec. 1500s had a 3.63:1 diff. Most GT6s had a 3.27:1, but that might be asking a lot of the original 1147!
But diffs are more plentiful and cheaper...and they'll also bolt right in. You'll have to change the u-joint flanges on the axles and propeller shaft, but that's about it.
Something to think about....
But diffs are more plentiful and cheaper...and they'll also bolt right in. You'll have to change the u-joint flanges on the axles and propeller shaft, but that's about it.
Something to think about....
Trevor Triumph
Jedi Knight
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It has been my experience that the fly wheel is different from the three rail transmission to the single rail. I think the bolts are a different size as well. The OD means that the engine will turn about 500 rpm less at highway speeds. T.T.
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Actually, the critical difference between three-rail and single-rail gearboxes is in the number of splines on the input shaft: 10 for the three-rail and 20 for the single-rail. But there are original Triumph driven plates that can be swapped back and forth to deal with that if necessary.