<VV> Early drums from Z car

[Bryan Blackwell]

On Nov 5, 2008, at 5:43 AM, Kenneth E Pepke wrote:

> Remember that brakes 'work' by converting energy of motion
> to heat energy ... rapidly collected in the mass of the drum or
> disc then dissipating that heat into the air over a period of
> time.

Yes, to a point.  However, if the drum can transfer the heat to the  
airstream well enough to stay below the point of fade, then the  
system will continue to work.  The difference is that aluminum  
transfers heat far better than iron - witness what happens on a water  
pumper when you change from iron to aluminum heads.  This same  
advantage in transferring heat should allow an aluminum drum to run  
cooler, even though its capacity as a heat sink is lower.

Bottom line - manufacturers used iron drums because they are  
*cheap*.  The Al-Fin drum was developed in the 50's to improve drum  
brake performance in performance applications before discs were  
practical.  Once discs became practical, there wasn't any point in  
making expensive drums, except for unusual applications.  I'm sure  
the Nissan engineers made these drums primarily to save weight.

>   Reduction of the mass reduces the drum or discs ability
> to store heat.  It is the reason that a drum or disc has a limit
> on how much it can be resurfaced.

I disagree.  The drum needs a certain amount of physical strength to  
withstand braking.  I'm pretty sure brake components are made as  
light as possible otherwise.

--Bryan