: Purpose for detent switch and kickdown?

06-13-11, 07:05 PM
Can anyone provide me with a quick run-down of how a detent switch works with the transmission for kick-down, why is it used, and what is it intended to help with? Why does the tranny need to kick down to a lower gear when the pedal is fully compressed?

I'm trying to get a better understanding for what the car is doing. Thank you in advance.

07-18-11, 11:52 AM
It is July now and no-one has replied. I'll give it a go, but it's been a while.

An automatic transmission or trans-axle attempts to do what a driver does with a manual tranny. Kick in the clutch, bring the engine revs up to meet axle speed, then shift into a lower gear for more torque for passing, going up a hill, etc....

The detent is the point that tells the automatic you need a down-shift for more torque. In the old days, it was accomplished with manifold vacuum. When the manifold vacuum dropped sufficiently, because you had your foot in it, the pull off didn't have sufficient vacuum applied and it released, throwing a switch in the tranny and making the transmission shift into a lower gear. This can be accomplished with a detent as well.