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MG MGB Technical - overdrive conversion

Hi everyone,
I have to remove the engine in my 1966 MGB for overhauling this winter. I was considering adding an overdrive to my 3-synchro gearbox while I have got everything out. Has anyone any experience of doing this and how hard is it to do?
Thanks

Jim
J Reckitt

It needs a replacement gearbox with the overdrive, and that means a longer propshaft - 31.125" in place of 30" - for a banjo axle, or 32" in place of 31.125" for the Salisbury.

Originally the 3-synch OD electrics included a relay and a vacuum switch to control when OD was disengaged as well as the manual switch and the gearbox switch, but the vacuum switches are NLA unless one comes with the gearbox. It's not essential, you can power it using just the manual switch and the gearbox switch.

Unless you have already found one I think you are more likely to find a later 4-synch, which can be mated to the 3-synch engine, with a modification to the top of the tunnel.
paulh4

My tunnel was also widened by the bellhousing on both sides.

It was fitted with an 18V engine and 4-synchro �box while SU still had it, although it may well have gone back to Abingdon for the mods.
Dave O'Neill 2

Widening the tunnel was done by the factory for the auto, it's not needed for the 4-synch. The only mod is to cut the removable top panel near the front and insert a filler strip, to move the gear lever hole back, as in the attached. You have to be sure to move it back enough or the lever fouls the edge of the hole in reverse.
paulh4

That�s interesting, Paul.

In that case, I wonder if my car could have been used for testing with an auto �box fitted?
Dave O'Neill 2

Who knows? :o)

Ha! No 'attached'.

paulh4

Who knows? :o)

Ha! No 'attached', I was sure I did ...



paulh4

Thanks for your comments everyone. I wasn't planning on changing the gearbox, so I think I will have to keep filling the piggy bank for a while longer!
J Reckitt

Jim, I love your surname for the work you're about to do. :)
Nigel Atkins

This thread was discussed between 28/10/2018 and 31/10/2018

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