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Q & A: 3 Syncro to 4 Synchro Box

Tuesday January 03rd, 2006
Q & A, MGA, MGB, MGC, MG T-Type, Midget
John,
1. I read your tech tips with interest. There is obviously little about
MGBs
that
you have not seen!

I have been told that the post 1967 4 synchro gearbox is more robust
than
the 3
synchro box with which my early 1967 MGBGT was fitted.

I have managed to get a 4 synchro box with overdrive, but the gear lever
comes
out in a different place (several inches back),
and I understand that the box may or may not fit in the narrower
transmission
tunnel. (without some help from a heavy hammer???)

What is your advice? Should I go through the hassle of converting the
gearbox
to fit the engine by fitting a later backplate, and remounting the old
starter
to match the old flywheel etc, or should I just keep looking for a 3
synchro
with overdrive if I want one?



2. Thanks for your reply. It was later than my decision, but welcome all the
same.

In the end, I opted to fit the 4 synchro overdrive to the 1967 MGBGT
because everyone I spoke to said that driving without an overdrive is hard
on the ears, and 3 synchro O/D boxes are as rare as hen's teeth.

I changed the engine backplate to match the new box, and fitted a new
flywheel and starter to match, and when I fitted the unit up to the body,
I
found that I only had to cut off a small corner (less than 2 in.) to clear
the starter motor.

Other than that the unit fitted well, with no further mods (the prop shaft
is the same length as the original one from the 3 synchro non O/D box)
except for the need to move the gear lever several inches backwards, which
I did by lengthening hole in the tranmission tunnel, and then cutting the
existing gear lever cover plate, lengthening it and fitting new "nutserts"
to bolt it over the longer opening.

I "recalibrated" the speedo roughly by measuring the speed at 50mph
against
another car, and then resetting the pointer to read 50 mph at that
deflection. This does result in an offset error at other speeds, but it's
the best I can do at home.

The car now works well, with a dash mounted O/D switch as originally
fitted.

Thanks

John
John!

1. My thoughts are: Don't do it -- because it corrupts the
originality of the car, AND, it doesn't fit very well.

If you want to fit it, you DO have to move the gearlever back
about
four ... read more