44 three reasons your drum brake will stick
three reasons your drum brake will stick
By Jamie Rogers on 2018-07-04 17:15:06
Despite most new cars using disc brakes, there are still one or two older cars or commercial vans that use drum brakes ñ quite literally a ëdrum´ in which two brake shoes are forced against (internally) to slow the vehicle down.
The mechanical side of it is simplistic, and truth be told, they are no way as efficient as the more modern disc/pad setup, but when set correctly, they work well enough to slow you down, although when compared against a modern setup, you tend to feel as though you´d be better off throwing an anchor out of the car.
Performance they´re not.
Understanding how drum brakes work is key to understanding why you may get problems, although you would usually find that the problems centre around inefficiency rather than sticking on.
As we explained, the drum setup usually consists of a cast-iron drum which is fitted over two brake shoes, operated by a wheel cylinder (usually hydraulic) that forces the shoes against the drum, adjustment is normally through a º´ square adjuster located at the back of the drum, although there are other, less-common methods.
The shoes are coated in a friction material, just the same as a brake pad, although usually less abrasive and less hardwearing, and more often than not, they take care of the handbrake also.
The most common reason for brake shoes & drums to be sticking is through mis-adjustment ñ people tend to adjust them to the point of almost binding, and then leaving them set that way. When the brakes get hot, the friction material expands more than the braking surface of the drum, which leads to the brakes binding on. Rectification is easy ñ just back the adjuster off slightly, usually around one quarter of a turn.
Although sealed within the drum, it´s entirely possible that the brake mechanism gets gummed up with the friction material, leading to them not releasing properly ñ just two springs (one top, one bottom) have the job of pulling the shoes from the braking surface, and when the dust from the brakes gets into the mechanism, these springs can struggle to overcome the added pressure. As the brakes heat up, the shoes tend to bind, leading to a catch-22 situation ñ the heat makes them bind, which in turn produces more heat, which of course leads to them expanding further and tightening up even more.
Finally, it´s entirely possible that the drum itself isn´t that round ñ due to the nature of the design, and the job that it has to do, the drum itself can end up being slightly oval. This means that the brakes may feel free at certain points, but when the wheel is turned a further 90 degrees, they find a tight spot, which the same as badly adjusted brakes or brakes that aren´t releasing properly will cause added friction, leading to a heat build up.
Drum brakes aren´t quite the same as discs and pads when it comes to maintenance ñ they need adjustment on a fairly regular basis, although thanks to not being quite as abrasive, then tend to last longer between replacement.
This means that if you´re quite handy with the spanners, you should always take the extra ten to fifteen minutes to check that the brakes are adjusted properly. Usually, cars fitted with drum brakes (which tend to be older or cheaper cars) incorporate the handbrake, so spotting when they need adjustment is easy ñ the handbrake isn´t quite as efficient, meaning that it needs more ëclicks´ to hold to the vehicle, if it holds it at all.
Having said that, you shouldn´t confuse adjusting the handbrake with adjusting the brake shoes ñ the handbrake is operated by a cable, and over time, the cable stretches and doesn´t apply as much force to the shoes.
Something else to be aware of is the wheel cylinder leaking fluid ñ these are little hydraulic cylinders that effectively operate a lever, pushing the brake shoes into the drum. When fluid starts leaking (which happens quite a lot), the wheel cylinder cannot push the shoes apart, meaning that you´ll get an inconsistent braking force to the wheels ñ the car will start ëpulling´ left or right under braking, and of course, the braking distances increase. Replacement cylinders are available, as are replacement seal kits (that fit inside the cylinder), but in all honesty, you´re much better off replacing the while cylinder, and doing both sides (instead of just the faulty one) makes for good practice.
Keeping your car in A1 condition doesn´t necessarily mean hours of work every weekend or hundreds of pounds in parts ñ regular check-ups, maintenance and inspections can make a huge difference to the reliability or mechanical roadworthiness of a car.
Part of the reason why failures are so expensive is because they´ve been allowed to get worse over time ñ imagine a brake pad wearing out, when caught in time, it´s a simple replacement, but if it goes unchecked, it can lead to damaged discs, hubs, wheel bearings, brake lines and even tyres ñ all for the sake of a five minute inspection.
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