Gents,

I have found the answer to a question I had about the parking brake, the drum style, not electric one with baby caliper.

The question is about the behaviour of such drum brake system.
01. Go to an incline, say 10-15 degrees where your car without braking will surely roll down the slope.

02. BASED ON AUTOMATIC TRANNY - Since our tranny selector is easy to go to P directly, usually we place tranny in P directly from D and then applied parking brake for additional safety. Turn off the engine.

03. Sometime later, you want to drive the car, turn ON the engine and then go for neutral and release parking brake, the car will jerk ( with pop sound ) a bit, not from the parking brake but the parking lock claw/pawl is under tension.
https://en.wikipedia.org/wiki/Parking_pawl

I explained how to avoid this for my driver in Bali, as my villa there parking space is sloping. So parking brake is a must use.
I hate hearing the jerk-pop sound.

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I knew about this, but I never knew the actual mechanical reasoning for this, except I assumed by parking brake bite ain't so good.
Boy, oh boy, the mechanical truth is the servo effect.
I accidentally got the answer when watching an old Toyota tech video by Toyota USA.

This is what is happening.......
http://theengineersjunction.blogspot...um-brakes.html






In summary, drum brake is NOT like disc brake.
Disc brake is instant, the moment the piston pushes the brake pad and squeezed hard on the rotor, car does not move even 1 millimeter.
In a drum parking brake, the good grip only occurs after the drum ( or tire ) has spin some degrees like I think 1/5 tire revolution at least and the brake shoe then gets its good grip
for the leading brake shoe towards the drum as servo effect starts to work its magic.

So apply parking brake first on a slope with tranny in neutral, let wheel rotate a tiny bit till brake shoe gets maximum grip, and then hit PARK on tranny.
This way the parking pawl is zero loaded, the drum brake pad is the one doing all the holding.
No jerk-pop sound later on when going to neutral from PARK, as the parking pawl is not under tension.

I hope this info is useful.

 

Yes, self-energizing brake pad/pivot geometry.

Thanks for posting.

 

The gear selector module responsible to relay the
< P R N D > selection is not built to withstand repeated stress of parking on hills.


glued half-shells: no fix! 😏

It is attached externally and is consumable. This module can't be opened to lubricate gears

Don't use the transmission as parking brake is an excellent advise