Automatics... what stops them

[dollywobbler]

^^^^Those things wear with gear changes, into reverse or D from neutral etc. Nothing wears when the engine is holding the car on a hill. But the oil does heat up. Quickly too if more revs are required for the hold.

 

Which is why it's better to leave an automatic in D at traffic lights rather than keep knocking it into Park or Neutral. I know who folk religiously switch into N or P for the merest pause, which is doing more damage than just leaving it in D. In a good car, the handbrake will hold it against being in Drive (the Colt for example). It becomes a pain in a car with a shit handbrake, as you end up having to keep your foot on the brake to stop the bugger creeping - and I hate doing that as I actually care about the retinas of the people behind me.

 

As for DAFs, they have a centrifugal clutch, so drive is entirely disengaged at tickover, hence the rollaway effect as Ray describes. It's pretty simple compared to a conventional auto.

[SiC]

Some autos (I know the AW55 used in Volvos/Saab/Vauxhall/Renault/others does this) if left in drive and the footbrake is applied, then it will put it in neutral until the footbrake is released. Releasing the footbrake sticks it back in Drive. The switch that detects it triggers before the brake is fully up, to try and reduce the time with no brake and neutral to the minmium. Done for fuel efficiency reasons apparently.

 

If I'm too quick on a steep hill, I can make the Laguna rollback slightly until it engages drive again. Really, really steep hills it can't hold on, so there is a limit to what is possible to hold on. I guess big diesel auto passenger cars should do better in this regard.