overdrive in a car

Does the car have a standard or an automatic transmission?

Either way, switching it on and off frequently doesn't seem to make a lot of sense, unless maybe you drive in an area where you're constantly changing from very hilly terrain to flat. It could cause the OD relay or solenoid to fail early, leaving you without OD until it is repaired.

Driving mostly with it off causes the engine to run faster for the same driving speed. Overall this raises your fuel consumption and - if all other things remain equal, which they never do - would increase the rate of engine wear due to more engine revolutions per distance travelled.

Aneuploidy wrote:

If it's an automatic then the only reason to turn the OD off is towing a trailer or going up a steep incline when the tranny is shifting back and forth a lot, otherwise the OD will only engage when cruising anyway so turning it off will only increase fuel consumption, won't hurt anything, just doesn't help.

Automatics should be left in OD unless desending a very steep hill, then put it into drive 3, or if the tranny can't make up its own mind of what gear it should be in... There is no performance difference.... Of course if you need to have a kickdown from 4 to 3 instead of being right in 3rd gear then yea, a split second.

There's nothing special about the pushbutton overdrive, it works just like any other 5th gear except you push the button instead of move the gearshift. It's kinda nice actually since you can downshift to 4th without touching the clutch if you want.

Hmm... but you need the clutch to bring it up tho?

You don't *need* to clutch to do either, but a lot of them engage pretty roughly if you don't, I usually clutch for both engage and disengage, there's been arguments both ways on this but it seems logical that taking the load off it before shifting would reduce slippage and wear. Disengagement without clutching is quite smooth though.

Cool...

I asked my dad about the overdrive button, but he said his 240 and two 140's didn't have it, they were 4 speed (he thinks the 4th gear was an OD, but isn't 100% sure, is this possible, or is it a direct ratio). He said our

The 740 had an AW-71, the button closes a solenoid valve that locks out 4th gear. You don't often have to use that.