> < snip> Triumph racing team who told me that
>a 3.27 ring and pinion gear set would only fit in a non-overdrive GT-6
>rearend. Thinking about it now that makes sense to me because the GT-6
>gear set is probably a lot more heavy duty to handle the additional
>torque.
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No unfortunately, that's not the case - the parts are the same (see below)
With the 3.27 gears though, It's not so much the Diff casing as the
internal ring gear carrier. These are machined different for the 3.27 ring
gear which requires about a .09 thousandths offset away from the pinion
gear than the *usual* ratios for them to fit. This also requires special
shorter, "thin head" bolts with NO lock washers and Loc-Tite to install
this gear set. If standard ring gear bolts with lock washers were fitted
they would foul the carrier bearing supports in the front housing because
the ring gear is so close.
***********************************************
>I purchased a non-overdrive GT-6 pumpkin with a broken 3.27 ring and
>pinon, and a new 3.27 ring and pinion. I traded my 4.11 rearend to the
>mechanic for installing the new ring and pinion into the non-overdrive
>GT-6 pumpkin I purchased.
***********************************************
I will however add that the GT6 internals ARE NO STRONGER than the Spitfire
(MK4 and up until 1976). The internal parts are all *basically* the same
(if you check they will carry the same Stanpart part numbers) and up until
around 1976 things weren't any different. After that there were some
changes mainly to the carrier itself (slightly stronger) to increase it's
durability I suspect because it was also used in the TR7. The TR7 also has
a 3.27 ratio used in the automatic, which would be a better choice as far
as strength, but you still have to transfer the internals (pumpkin plus
ring and pinion) to a Spitfire/GT6 outer casing. Unfortunately, while the
front half of the TR7 (small diff units) are *almost* identical to the
Spitfire/GT6 it doesn't have the required four front mounting bosses, and
the threaded holes to mount the Spitfire/GT6 front plate. A pity, because
if they were there one could simply unbolt the front half from a TR7 and
install it in the rear half of a Spitfire/GT6 housing and be done!
Not to be the bearer of bad news, but no matter how well you have it setup
it will fail. It may be quite awhile, but it's not a matter of *if* but
when. Chances are when it goes, it will be the carrier casting that fails -
I have a feeling that the 3.27, because of its ratio, puts less of a strain
on the internal components (as opposed to the lever arm of a say 4.11) and
that leads to less overall stress. However, with that much horsepower
everything changes, although you can't really apply anymore internal stress
per say than the tires would allow anyway. When the tires loose traction
and spin, that's the max loading you would incur at that point - no matter
how much horsepower you got! Usually when one installs a larger engine,
one also installs bigger tires. If you don't go overboard you shouldn't
have any problems.
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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