[Mgs] Determine build date for an O/D transmission?

Andrew Lundgren lundgren at byu.net
Mon Nov 11 06:35:54 MST 2019

I have a '78. The transmission is a blue label, but the seller doesn't have
the shift lever.

A lever for a '78 is not a cheap thing, and my son who is driving it a lot
right now likes the Walnut MG logo shifter it has.  So I'm looking at
options for how to install the O/D switch.

>From the moss catalog, it looks like the '76 switch won't work with the
'78. So I might have to buy the parts to put together the shifter switch or
put it in the blank accessory switch above the fan on the dash.

On Mon, Nov 11, 2019, 1:45 AM PaulHunt73 <paulhunt73 at virginmedia.com> wrote:

> None of that is to do with the OD itself.
> Which gears it operated on is a function of the linkages on top of the
> gearbox, and you can have it on 3 and 4 or 4 only as you wish.  When the
> TCSA was introduced in late 76 to control 'surging' a third switch was
> added to the top of the gearbox that operated in 2nd and 4th, and this was
> wired in series with the OD switch operating in 3rd and 4th to produce a
> 4th gear only output controlling the TCSA and vacuum advance.  I suspect
> that was not very reliable as it was an external micro-switch so it was
> deleted and the gearbox components changed so the switch operated in 4th
> only, as done to the V8 several years previously.  The gearbox switch now
> controlled both OD and TCSA.
> The gear lever itself changed for the 77 model year to incorporate the OD
> manual switch, but that can also be fitted to any year, or the 77 converted
> back to some other switch, as you wish.
> The wiring prior to 77 was from the manual switch on the dash or the
> column, to the gearbox switch on a yellow and a yellow red, then from there
> to the solenoid.  For 77 on it was from the ignition supply on a white to
> the gearbox switch, then from there to the manual switch on the gear lever,
> and from there to the solenoid.
> Black label or blue label determines which speedo is compatible - black
> label was used on CB cars and used a 1280tpm speedo.  Blue label was used
> on RB cars and used a 1000tpm speedo.  But speedos can be recalibrated if
> you end up with the wrong combination.
> So as a 78 it should have a blue label OD and the manual switch on the
> gear lever, as the column switch - which together with the plastic dash was
> new for the 77 model year - won't have that function.  But if the car has
> the earlier RB dash and column switches you don't need the gear lever
> switch, which is prone to shorting out and causing harness damage.
> PaulH.
> ----- Original Message -----
> Not so much. It will be a a bit still until the transmission arrives.
> (Freight from NY to UT) I'm just trying to figure out which shifter it
> should have had as well as which gears it should work on.
> I'm going to be putting it into a 78, but the current owner is still
> trying to track down the shifter from his friend, the previous owner. He
> doesn't know if it was a late shifter or an early one.
> I'm trying to determine how to wire it in.
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