[Mgs] Another way for engaging the O/D

Bert Palte palte at gmx.net
Mon Nov 11 10:30:38 MST 2019


Using a relay for latching, you may consider using just a (non-latching)
pushbutton to engage the O/D.

Assuming the O/D works only on 3rd and 4th gear, you don't even need a
(second, NC pushbutton) switch to disengage the O/D.

Just move the gear lever to between 3rd and 4th and then just a very
short time to the left to let the relay disengage and thus to have the
O/D disengage.

(Similar as in my 1972 Sunbeam Sceptre. In that car, there is a stalk to
the R/H side of the steering column.

Stalk momentarily down = engage; momentarily up = disengage. I never use
the "momentarily up" function;

I always disengage as just described. Very convenient!)


70 B

Op 11-11-2019 om 17:08 schreef Charley Robinson via Mgs:
> 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,
> CR
> 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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