old volvo transmission question

[MajesticMoose]

I know someone that has an '81 volvo 240. It has the m46 transmission with laycock overdrive. basically it's a 4 spd that you push a button on to get a 5th overdrive gear. Can anyone explain how it works, or tell me where i can find out? Does it have some other clutch inside or something?

thanks,
m00se

 

[NutBucket]

Exactly. Its a 4 speed tranny with a planetary fifth gear stuck on the back. When you hit the overdrive button on the top of the shifter, and electronic clutch engages and poof! fifth gear. So effectively, you've got 8 forward speeds. I think there's some sort of relay that prevents you from using OD in any gear other then 4th.

 

[TonyH]

The O/D switch probably passes through another switch on the transmission that works off the 3/4 shift rail. Much like back up lights do in some transmissions.
That way the circuit to energize the soleniod to shift into fifth would only be completed with the transmission in the fourth gear position.