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If you compare the drum to the disc, I agree. The caliper piston is heavier and more complex. The caliper assy must ride on a slide/carrier and there are slider pins, seals and caps. The works need to bolt to the steering knuckle or equivalent. The drum brake simply gets bolted up with the hub bolts. There is a fair amount of machining for slides and complex shapes.
While drum brake assys appear more complex, many of the parts are inexpensive castings.
Most rear disk brake assys have a drum brake for a parking brake. This feature already has the part count of a full drum brake. The assy costs will be the same.
The discs can easily be heavier, creating increased 'thermal mass'.
Both are made of cast iron, not steel. However, I think that most drums have stamped steel flanges with iron cast onto that.
As a drum heats up, the shape of the swept surface is no longer cylindrical. It becomes slightly conical. These affects the friction performance.
Because of weight transfer, rear brakes do not have much work to do. Many vehicles are front heavy. Needing to avoid rear wheel lockup, the braking effort is relatively low. With non-ABS systems, the brake balance was worst case and the rear brakes did even less work. With ABS, the system can take the rear braking effort to the tractive limit when required.
Disc brakes are better at dissipating heat. Typical driving will not create problems with drum brakes. However, when going down a long downgrade in the mountains, the rear drum brakes can overheat and a small engine does a poor job of energy dissipation when shifting to low gear.
posted by 69.150.153...
, Thu, 29 Mar 2012 06:12:08, Wed, 28 Mar 2012 20:31:01
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