Alun,
All the GT6 and Spitfire 3 rail four Syncro gearboxes have a "noisey" first
gear. This is caused by reverse teeth on the 1-2 shift hub making
incidental contact with the reverse idler gear when the box is shifted into
first gear. It seems to be part of the design as there just isn't enough
room in the casing to prevent the contact. If the reverse idler and 1-2
shift hub gears are not "bull nosed", but are still sharp, then this noise
usually isn't bad. As they wear however, it makes more noise, eventully
sounding like you have a "loose" gear in first. You may even feel some
vibrations in the shifter in first. This can also make shifting into 1st a
little tougher as it has to whack the reverse idler gear into mesh as well.
If the bearings are quiet, and it syncro's downshifting into 3rd and 2nd,
then leave it alone. The replacement bearings and syncro's that are sold for
these boxes are junk. The RHP bearings right out of the box have "rough"
spots in them and the later syncro's (71 and up) just don't work. They are
physically too large to properly syncro. It is a weak spot no doubt. But
with proper oil, it should last just fine. If you want to re-build it, then
find an old spitfire MKIV gearbox in good shape and strip it for parts.
These are usually very inexpensive, compared to the GT6 box, and usually
show very little wear. You can strip the syncro's bearings and the shift
hubs out of it if your GT6 box has worn parts. The gears aren't the same ,
with the exception of the reverse idler, so don't even try.
The 2000/ 2.5 box, while it will fit, is much larger, and requires
modifications to "make it fit". Also you lose the nice close ratio's of the
GT6 box.
Steve Harris
Treasurer Cape Cod British Car Club.
From: "Alun Bain" <MPArun@minorplanet.com.au>
Subject: GT6 Gearbox
I have recently purchased a Mk3 GT6 and I have been told by quite a few
people
that the gearbox is very weak. can any other gearbox be used without too
much
modification? does the 2.5 PI/TC engine and gearbox fit in without much
trouble? is it at all worth doing? First gear is noisy and doesn't engage
as
easy as it should, the other gears are fine and I want to get the gearbox
fixed but if there is an option to upgrade the gear box (and maybe the
engine)
I would be interested to hear your thoughts...
Alun Bain - 1971 Mk3 GT6
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