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MG MGB Technical - 3 synchro/ D-Type O/D manufacture date?

Hi everyone.
I've just pulled my gearbox from my 1965 MGB in preparation for rebuilding the box and overdrive. Like all Australian assembled MGBs until 1968, my car had a non-overdrive gearbox originally. I purchased the gearbox we've just removed in the UK when I was working there in 1984. (They were relatively plentiful then. The motor breaker/wrecker had two lying on the ground when I called by. "just pick on of them" he casually said!)
Just out of interest, I'm wondering what the date the box was built is. The solenoid (long since replaced), from memory was stamped "?/66" and therefore I'd imagine was made in 1966.
I photographed the Laycock plate on the side of the overdrive tonight. The final digits stamped are: ....../ 019673
Would this imply the overdrive was built in March 1967, or are these numbers just in a numerical sequence, unrelated to the date of manufacture? There's of course a 1st/2nd plane lock out switch on the top of the gearbox case, but no place that I can see for a reversing light switch, so I'm thinking the box was probably originally built in 1966, like the solenoid.

(I've gradually over the years collected a genuine 2nd gear steel synchro ring and a matching original genuine 2nd gear, a BL 4 hole layshaft, and a set of genuine matching layshaft bearings, and these will all be incorporated with the rebuild. If the box still has the earlier layshaft, we intend to ream the housing to accept the 4 hole shaft).
T Aczel


T Aczel

That plate carries the OD type and serial number info.

The solenoid could have been replaced before.

The gearbox should have a serial number somewhere, which in theory originally could have followed the engine number sequence. But with two types of main gearbox for non-OD and OD for the 3-synch that complicates matters.

I suspect it is lost in the mists of time ...

Could always ask these people - did a super job on the Marathon MGB Overdrive.
Staffed by ex-laycock employees
G R Wilder

Thanks Paul and "G R".
The gearbox has been taken apart now. All in all, things are not too bad in there.
It has the earlier "3 hole" layshaft, but the (blanked off) aperture for the reversing light switch is present. So I'm guessing the circa 1966 date on the solenoid probably was close to the date the gearbox was originally built.
As anticipated, the overdrive cone clutch needs replacing.
The Mk I MGB was only offered with overdrive in Australia in its final year of production here (1968, till August, and long after UK production had changed to the Mk II. I suspect the parent company used us colonials to offload superfluous superseded Mk I MGB stock, just as they did a few years earlier with the MGA 1600, but I digress...).
However as a result, parts for the 3 synchro gearbox/D-Type overdrive combination verge on the "unobtainium" here.
So thank you very much indeed for the link Mr Wilder, I've sent an email to order a new overdrive cone clutch to "Overdrive Repair Services".
T Aczel

Ironic that the had so many home market cars with OD but failed to send many to the colonies where long high speed autoroutes cried out for them!
Bill Spohn

This thread was discussed between 24/05/2017 and 26/06/2017

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