back in the day when general motors spent a lot of money training me,
we had two kinds of automatics, the (in)famous gm hydramatic which was adapted by rolls royce, and the borg warner t35, which became a famous
racing box later. then came the powerglide which was gm's 3 speed hydra, and eventually formed the basis of the transmission in the famous chaparral racers of can am and lemans fame.
the basis of an auto is the speed at which the oil is thrown between the vanes of the clutch, as the speed falls, the oil pressure lowers, and the vanes have less drive and drag. in principal one takes ones foot off the throttle at lights, thus there are no real strains on the hydro clutch.
having driven autos for 30 years, the change back to manual a couple of years ago caused a major change in my driving since i had left foot braked for all that time. kind of embarassing to have no drive when you hoped to be stopping
although historically manual boxes were more economical than auto, these days, the fact that so many auto boxes have more than 3 gears and the computer chips which check the various things like mixture and air intake etc mean that in most cases the difference is no where near the 10-15 % it used to be.
many of the manufacturers have auto switch of devices for long periods,
in particular VW, others like cadillac now have devices which reduce the number of cylinders in use, this is because it is easier now with electronics to get the engines working at their optimum for most conditions, hence the ability to run at some speeds on fewer cylinders. in the case of vw, they automatically re-start when the throttle is depressed again to move away.
whilst i understand that many auto boxes are quite expensive to repair, they have become so standardised and so common, that often the repairers just rebuild one or two and swap them into the relevant cars which come in, hence reducing costs and timescale. and in many cases
for instance certain ford mondeos in the early days, the clutch change was about 600 quid for a 90 quid item because designers had forgotten they need changing, particularly after hill creep, or speeding off from the lights :twisted: :lol:
anyway my feeling after all this time is that leaving it in drive for a short time on the flat at lights is not going to create too much wear, not least since everything should be running in oil, it will maybe cut brake life, but not dramatically unless you have your tickover set very high, certainly easier than judging the clutch throttle ratio at lights.
:?
paul :wink:
