IML: Disc Vs. Drum

[Jeff Cantor <jcantor791@xxxxxxxxxxx>]

I'll add two more pennies to the discussion.

First, with regard to brake fade.  Brake fade in drum brakes is due  
to the heating and subsequent expansion of the brake drum which moves  
it beyond the reach of the shoes.  In disc brakes, the expansion of  
the rotor moves the friction surfaces CLOSER to the pads rather than  
further away thus minimizing the impact of long or repeated stops.   
It was stated in one previous post that disc brakes are better at  
dissipating heat.  While that may be true, it is the direction of  
expansion rather than the direct ability to handle heat that is of  
interest here.

Second, the effects of water.  While most of the cars we are  
discussing here seldom if ever see any wet weather anymore, water,  
particularly standing water, and drum brakes don't mix very well.  I  
can still remember as a tot riding in my folks 71 Coronet with all  
drums and being snapped around when the brakes grabbed when my dad  
had to slow down right after we went through a puddle.  He used to  
point out to me that it was a good idea to ride the brakes very  
lightly for a second or two after going through standing water in  
order to boil off the water that got into the drum and might make for  
unpredictable stopping.  Disc brakes don't have this problem.  Any  
water that gets onto the rotors when the car is moving is flung off  
immediately by the rotation of the wheel whereas in a drum system,  
this water gets trapped until it boils off with the heat.

All that being said, the factory brakes on our cars were all very  
good or excellent for their day and, so long as one still drives with  
the respect and moderation that the original owners most likely used,  
are more than sufficient.  On the other hand, if your goal is to turn  
your 30 to 50 year old Imperial into a daily driver that can safely  
navigate today's suburban and major metropolitan areas during rush  
hour on a regular basis, disc brakes may offer some advantages.

Jeff
'56 Sedan (with recently redone 4-wheel, center plane drum brakes)
Trenton, NJ


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