There is a saying that the table is round. In the case of brake systems on pickup trucks, this means that what fell from favour a decade ago is back.
In case you haven’t read the specifications sheet for the new Dodge Durango, Dakota, some Ram pickups, or the sheets on 2006 Silverado-Sierra trucks, drum brakes are going to be standard on the rear axle. No disc brake options.
You might point out that you’ve been told discs are better and you’d be right, but not necessarily accurate. To figure out what works best and what is going to be used are two different things.
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Way back when, the first brakes were leather bands that wrapped around the drive shaft. Since this system only worked well a couple of times before needing to be replaced, harder materials were used next. The issue of wear still existed because of the heat created with the friction of stopping.
Next, the brake moved to the rear wheels, one on each wheel to be exact. These new rear brakes were a novel design. They used “shoes” inside a drum and they expanded to push against the drum, creating the friction to bring the vehicle to a stop. Since the braking surface was much larger, stopping improved. Getting rid of heat was still an issue and brakes were still subject to fade if used excessively.
A few years later, with the implementation of hydraulic systems, drum brakes were added to the front wheels. Another huge improvement in stopping ability was logged. Improvements to drum brakes over the years included self-adjusting systems so that near daily maintenance wasn’t required.
Then power assist systems came on line, so you could work the brake pedal without having 25-inch thigh muscles.
Somewhere in the late 1950s, disc brakes began to appear on exotic cars like Ferrari and Jaguar. By the time the early 1960s came, these cars had disc brakes all round and the idea was that four-wheel discs gave more consistent and better stopping power than drum brakes.
Today most up-market vehicles have four-wheel discs, because everyone wants to have the best. The trouble is, except for a narrow range of applications, discs on the rear are no better in stopping than drums and are more expensive to maintain. Disc brakes are at their best when the workload is the highest.
According to Gerry Malloy, a retired General Motors engineer, disc brakes on the rear are better than drums when the vehicle is loaded to capacity and heavy, repetitive braking is required. If you look at the usage patterns of trucks on the Prairies, this situation does not arise often.
Now you have to add in a couple of physical factors, the first of which is that by design, disc brakes require air movement around them to cool properly. At the rear axle, this air flow usually has more contaminants than at the front. Gravel kicked up by the front wheels and water off the road are directed into the working parts of the brakes.
Second, said Malloy, “drum brakes need the same cooling to be effective, but the air flow is over the drum, which protects the working parts of the brake.”
Other problems have cropped up as well with rear disc systems. GM once issued a recall for thousands of Canadian pickups with rear disc brakes, saying that road salt may cause corrosion that forces the ABS sensor away from the wheel, rendering it unable to read wheel speed correctly. The end result is the ABS system comes on at the wrong time, resulting in extremely long stopping distances.
Now let us look at the one item near and dear to the hearts of the manufacturers – cost. It costs less to put a drum brake system on the back axle than it does a disc system. With the numbers of trucks produced and the rebates now in place, it doesn’t take much of a saving to get a company to seriously consider changing over.
In GM’s case alone it produces about 1.4 million trucks a year and a saving of $5 per unit is huge dollars on a year-by-year basis. In addition, if you add in the cost of the current recall and any future ones, the savings multiply quickly.
This whole issue, if handled properly, can be positive for everyone involved. The company saves money in manufacturing and warranty, while you don’t have as much down time for unexpected service. Safety is not compromised and stopping distances are the same.
On the psychological side, not having your truck fail means that you will most likely come back and buy another one from the same company. Brand loyalty is a big deal these days, particularly now that trucks are the largest profit centre that manufacturers have.
Charles Renny is a freelance automotive columnist and a member of the Automobile Journalists Association of Canada. The opinions expressed in this column are the personal views of the writer.
