Sonic'

Quick question on Overdrive on Auto boxes

just got a Toyota Previa (1996) with an auto box, and it has an overdrive switch on the gear lever

Previously I had a 1993 Shogun Auto, which also has an overdrive switch on the gear lever

Now should that overdrive button be on all the time or not ?

The handbook isnt very clear and just says use it if you want better fuel economy, my Dad reckons I should only switch it on when I am going over 30-40 mph, I always left it on on the Shogun

So which is the best way to use it ?

NotoriousREV

If the autobox in the Previa is similar to the autobox in my Soarer, having the switch in just allows the box to use top gear whereas not having it in keeps it in 3rd.

I suspect your dad thinks the overdrive is like the old overdrive units you got on old British cars and vans (I used to drive my mates Transit with overdrive available in 3rd and 4th so it effectively had a 6 speed box)

Sonic'

Yeah thats what I was trying to tell my Dad, he is old school

He said the overdrives he knew actually disengaged the gears and was a straight through drive

But I suspect in the Previa & Shogun that it does just put it in 4th gear

Shark Man

Bit of a gimmick to overcome the shortcomming of a stupid gearbox which changes into top gear too soon and unwiling to downshift once its there. Its no different in construction (or gearing) to an automatic gearbox without an overdrive switch.

All it does is just lock out 4th gear (or 5th if its a 5 speeder) and sometimes prevents the torque converter locking up (depending on design), works like if you select "3" on the shifter on automatic cars without a switch.

Basically overdrive=off in city traffic (sub 40mph) And "On" any other time.


My Land Rover has a "true" Overdrive...its a seprate overdrive gearbox bolted onto the back of the main gearbox (orginally manual...now 3 speed auto), can use overdrive in 1st, 2nd or 3rd....and reverse. Also works when the transfer box is in low range, so thats 12 different forward gears to choose from and 4 reverse gears

Sonic'

Cheers SM

Had a gearbox like that on the old Terex Trucks I used to drive on the open cast mines, although they had 12 forward and 6 reverse