LH Overdrive

[David Ramsbotham]

Hello All, can anyone tell me the differences between a “black” and a “blue” cover plate overdrive unit and if they are interchangeable?
Many thanks, David.

[David Ramsbotham]

Think I ‘ve just answered my own question! Black goes with 1280 tpm speedo whereas blue goes with 1000 tpm speedo as drive gears in overdrive units are different.
Anything else? David

[steve00136]

Found this link that explains the difference as well at https://mymgbinfo.wordpress.com/2019/01 ... ox-mgb-gt/ just taken my gearbox out.

[Peter Cresswell]

Although you can use a blue Overdrive in car that had a Black overdrive originally the speedo will be wildly inaccurate. In theory a Blue LH Overdrive can be rebuilt as a Black LH Overdrive and vv. The speedo drive gear needs changing, but the only way you can do this is to use a overdrive specialist as you need a lot of specialist tools to dismantle and reassemble the unit. There are not many specialists in the UK (3 I think) that deal with Laycock Overdrives, but I have used ODSpares in Rugby who I have found to be very good.