Jim Cathey wrote: >> totally OT question - how did that electronic OD work? > > My guess is the usual: a bolt-on planetary gear with a solenoid > to engage/disengage a clutch on the outside. A planetary gear, > with nothing pinned down, doesn't change the gear ratio.
That's basically it, as far as my limited understanding goes. It was manufactured by Laycock, so Googling "Laycock overdrive" will probably find a description of its internals. The same unit was used on Triumph TR4s and some other cars. I can't quite visualize how it works; I get lost somewhere in all the talk about Sprague clutches and such. In stock form there's a 4th gear interlock switch to prevent it from engaging in any gear but 4th. I'm told bypassing the switch isn't a good idea as the overdrive doesn't take the greater torque in lower gears very well. Also, trying to back up with it engaged is said to destroy it almost instantly. Interestingly enough, early versions of the owner's manual say that clutching while shifting the overdrive is unnecessary, but suggest pushing the clutch in slightly to smooth the shift. Later versions unequivocally recommended pushing the clutch in fully. Perhaps there were some wear issues with unclutched shifts? Mine was a bit worn, which made it slow to engage, but it worked very well otherwise. The 4-speed plus overdrive is said to be sturdier and longer-lived than the conventional 5-speed that followed. Apparently the 5-speed had some lubrication issues.
