Originally Posted by BonzoAPD
I have never heard this. Can you post some information on this?
I for one wouldn't use a parking brake on an auto. My first car was auto and my parking brake use to get stuck and hence lock up the rear brakes, wear then down and then i would have no brakes left in the back.
I have talked to numerous mechanics who have said a parking brake is useless in an automatic car unless you are on an insane incline.
Here's the background info I have on this. Keep in mind my region of CA is very hilly in general, so the loads and rate of failure are probably higher.
In conventional automatic transmissions, a sprung parking pawl engages a detent in the tranny's output shaft and prevents the shaft from rotating. But the pawl isn't designed to carry the entire load of the car. That's why the parking brake is designed as the primary system for keeping the car stationary. The parking pawl serves a secondary system.
If the parking brake is not engaged, and the vehicle is on any sort of an incline, the parking pawl will be under load as the wheels try to rotate, which causes the output shaft to rotate until the pawl locks the output shaft up.. hence the roll-back behavior.
Eventually, the pawl & it's engagment mechanism are damaged by this excessive load and the results are messy. In some cases, the pawl will fail, causing the car to roll away... in others, the parking pawl may fail to retract.
In either case, the damage is extensive.
Now how a manual handles these loads is another story for another time.
h: