Standard/Heavy Duty brakes???

[Doober]

I was looking at the Rock Auto site, and came across something I didn't know about/realize... apparently there was a 'heavy duty' brake option on only the '79-'80 Malibu. Could this have been part of the deal on the 9C1 Malibus?

Up until now the only ones I knew of were single- and dual-diaphragm boosters.
single

dual

"heavy duty"

I looked at Autozone's site and they even list it there, but there is no other HD-option brake part for the car... something strictly to do with the booster/master cylinder maybe? :-k

 

[DOUG213XRJ]

Im not seeing a differents.

 

[Doober]

Looks like the only major difference is the booster. I can only find one master cylinder listed for any given year.
Also, for anyone curious, the listed bore size for power brakes is 24mm, and manual brakes is 21.4375.