I took parts to the new shop for the MGB today. I noticed a round module on the firewall, about two inches in diameter, with a tube sticking out of the top. i was told that it was a vacuum device for the overdrive. I know basically how an overdrive works: it allows the engine to rev more slowly at higher speeds. The final drive is something higher than 1:1; thus, ‘overdrive’. And I know that the Laycock de Normanville overdrive is electrically activated. Flip a switch in 3rd or 4th gear, and it kicks in.
They were jerking your chain. Either that or they are idiots.
I have taught rebuilding LdN o/drives, and just to be sure, I went out to the garage and I now have in my hands a factory workshop manual for an MGB.
The O/Drive does not use vacuum. LdN units use only electricy.
Was this a small copper item about 3/4" in diameter with a copper pipe coming out of the top and bottom? IIRC this is a vacuum capsule for the vacuum advance on the distributor. One end of the pipe should lead to the intake manifold, and the other to the vacuum capsule on the distributor.
If you have any further questions about how it works, feel free to ask.
I didn’t see the back of it, as it was mounted to the firewall. It had a black plastic cover about 2" in diameter. The tube sticks straight out the top and is about 1/4" dia.
I could have misheard about the o/d. I don’t know much about engines other than the cycle, and I tend to glaze over when people go on and on when it’s after noon and I haven’t had breakfast yet.
understood about the glazing over.
Your description does not ring any bells. Picture?
Oh and to answer the question you asked in the OP How does a Laycock de Normanville overdrive work?
The answer is quick well actually. We used to call it the most reliable part of a British car.