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MG MGB Technical - Do I have overdrive?

I have a rubber bumper 74 "B" and I need a new steering collar wiper switch. I noticed that all of these switches are listed as combination overdrive switches. I'm guessing this activates when the switch is pulled towards the driver as I don't know what else this position is for. How do I determine whether I have overdrive? Also, my Haynes manual refers to a Type D and a Laycock Type LH. If I have overdrive how is best way to be sure which one?
Tom

Tom,
The surest way to determine if you have overdrive (OD) is to crawl under the car and look. If you have a bulbous cast aluminum housing inches away from the driveshaft, you do. If the tail end of the transmission is slender, you do not.

Type D OD's were only used on the non-synchro first gear transmissions fitted up through the '67 model year. From 68-74 the LH 'black label' was fitted. From 74.5 onwards (all rubber bumper (RB) cars) used the LH 'blue label'. You should have an LH 'blue label' OD - if fitted.

All North American bound MGB's from 68-76 had that style combination switch whether they had OD fitted or not. Having the switch is no indication that the car currently has, or ever did have, OD fitted.

HTH - Tom
Tom Sotomayor

If you need the switch, then there is only the one. As Tom says the same switch was provided regardless of whether OD was fitted or not (up to 77 anyway when it moved to the gear lever), and some of those with cars without have used the switch as an anti-theft device.

The engine number prefix indicates whether an OD gearbox was originally attached to that engine or not. But the engine and/or gearbox could have been changed to an earlier or later unit and hence an earlier or later gearbox and OD could be installed than the *car* year might otherwise indicate. However if the 'wrong' gearbox and OD has been fitted unless the speedo is changed as well the reading will be off as the gearing differed for each type of OD. OD was only ever an option for North America although it came as standard on UK cars from 76. Opinion seems to be that very few North American cars were fitted with OD for some reason, and even if it has the 'lump' there is no guarantee it works!
Paul Hunt 2

This thread was discussed between 13/12/2007 and 15/12/2007

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