> A friend wants to upgrade his street TR3 to later all synchro gbx
>
> Any problems in doing this??
Nothing insurmountable. The 4-synchro box is about 3/8" longer, so he'll
need to elongate the holes in the rear crossmember to move the rear mount.
For a TR3 (& TR3A to TS50000), he'll also need to modify the tunnel
slightly, to clear the larger starter bulge (later 3A/B already have this
change).
Depending on the vintage of his new gearbox, he may need longer studs in the
back of the engine (as the flange got thicker during the TR6 run), also
longer bolts for the rest of the joint.
Some advise changing the input shaft to the slightly longer TR3 version, but
I found that the TR3 input shaft will not mesh with later TR6 gearsets; and
the TR6 input shaft works fine for me. If he's keeping the TR3 clutch, it's
probably worthwhile to change the gearbox front cover to the slightly longer
TR3 version (and of course use the TOB that matches the clutch).
The all synchro boxes lack the dipstick/filler found on the early ones, but
it is possible to rebuild an early cover with the later forks & shafts to
keep the dipstick (if he chooses, otherwise the fill plug on the side will
work). If he keeps the later top cover, it may need to be drilled to accept
the through-bolt for mounting the TR3 gearshift (of course, keeping the
later gearshift is another option).
If it's a late TR6 box (after approx 73), the speedo drive gear will be
wrong. I don't know if the TR3 gear can be used or not, but maybe.
Personally, I like the wide brass bushings that the TR3 used to carry the
clutch cross shaft, so I replaced the narrow TR6 bushings. But that's
purely optional.
HTH
Randall
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