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

Charley Robinson Charley38 at twc.com
Mon Nov 11 09:08:34 MST 2019

I've swapped OD gearboxes into two CBBs.  In both cases I used the gear 
levers from the original non-OD transmissions.  I don't see any reason 
that you can't use the gear lever you already have for the OD box.

As to the OD switch, I'd put it on the dash if I had an open spot for it 
that was handy to my right hand.  In the CB cars the wiring and switch 
are already installed but there's no reason you can't find the white 
circuit that Paul mentioned and run a wire from it to your switch and 
from the switch to the lockout switch on the OD box.  Looks like there 
are a couple of switches in the Moss catalog that would look OK on the 
dash.  The switch is just a SPST that can handle the solenoid current.

My $ .02,


On 11/11/2019 7:35 AM, Andrew Lundgren via Mgs wrote:
> 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 
> <mailto: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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