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Re: MGB overdrive

To: MG List <>
Subject: Re: MGB overdrive
From: Max Heim <>
Date: Fri, 10 Feb 2006 10:21:13 -0800
On the subject of this alleged metal-bashing: I installed a late 4-synchro
tranny with LH overdrive into my 66 B, and I did not find a need for any
"metal bashing". It seemed to fit the tunnel just fine, width-wise. The part
that requires metal work is the top of the tunnel, since the shift lever is
moved about 4 inches further to the rear. It would seem to be simple to cut
a new hole, except for the fact that the 66 has a separate bolt-on top piece
for the tunnel, and the hole would have to be located right though the back
edge of this piece. British Automotive <> sells an
elongated plastic cover that is a tidy solution to this problem. You only
have to cut out the back edge of the opening a little with a hacksaw.

One warning about this conversion -- you will no longer be able to use any
fitted tunnel carpet kits, since the profile won't match either standard
configuration. For a totally tidy "factory" look, you would have to hand-sew
or glue a complex shape. I just padded it out with extra carpet padding, and
added a few snaps.

I don't know about the prop shaft issue -- seems to me I used the old one.
Maybe that is because I was going from early/non-OD to late/OD. I seem to
recall there were 4 propshaft lengths, for the different combos, and some of
them were so close as to make no difference.


Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires

on 2/10/06 9:05 AM, Paul Hunt at wrote:

> A Mk1 66 (3-synchro gearbox) originally had the D-type overdrive as an
> option, whereas in 67 the MkIIs (4-synchro gearbox) got the later LH-type.
> The later one will probably not fit the earlier gearbox.  The D-type came
> with a vacuum switch and relay to delay disengagement of OD if there was
> high manifold vacuum i.e. on the overrun at high-ish rpm to overcome an
> inherent weakness in the design.  The transmission tunnel was wider on the
> MkII cars to accept the 4-syncro gearbox, so you can't put a later gearbox
> in an earlier car without some metal bashing.  The later seats may also have
> been narrower/tapered to fit beside the later tunnel.  The OD prop-shaft was
> also 2.7cm longer at 78.9cm as opposed to 76.2cm.
> PaulH.
> ----- Original Message -----
>> I am going to pull my engine and transmission from my 66 MGB this summer
> for
>> a complete rebuild.  I am considering installing an overdrive which it
> does
>> not currently have.

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