The handbrake no longer holds your car on the slope in front of the house, and the brake pedal feels a bit deeper than it did last year? If you drive a Polo, Fabia, Clio, Corsa, Punto or an older Golf, you most likely have drum brakes on the rear wheels, and they send their warning signals differently than the discs up front. In this tip we walk through the symptoms of worn shoes, the quiet failure of the wheel cylinder, and what the handbrake reveals about the condition of the rear axle.
Why drum brakes are still around on the rear wheels
Many people drive for decades without realising their rear axle is still on drums, because the front brakes overpower them in everyday driving. The reason manufacturers keep the drum system is simple. The rear axle takes a smaller share of the braking force, around a third, so it is not economical to fit expensive discs and calipers to a wheel that does less work.
A drum brake has one practical advantage that a disc does not, and that is an integrated handbrake. The handbrake cable pulls a lever inside the drum, which pushes the shoes apart and locks the wheel. That is why cars popular in BiH, from the Polo and Fabia generations to the Renault Clio, Opel Corsa and Fiat Punto, still use a classic drum with a cable rather than the electronic parking brake found on more expensive sedans.
In other words, the drum is not outdated tech but a sensible solution for a job that is not demanding. Like anything mechanical, though, it has its weak points that you need to catch in time.
Symptoms of worn shoes and a damaged drum
Brake shoes, or as the trade calls them brake linings, wear more slowly than the front pads because they do a smaller share of the braking. Still, once they wear past the specified limit, they start sending clear signals. The most common is scraping or metallic clunks under light braking, especially at low speeds when you are pulling out of a parking spot. That is the lining that has worn down to its backing, and the metal part is starting to scrape the inside of the drum.
The second common symptom is the car pulling to one side under braking, but only at the rear, which you will feel as a slight sway of the back end while the rest of the car tracks straight. Usually one shoe is in significantly worse shape than the other, or one drum is overheated and grips unevenly.
The third sign is the smell of hot brake material after long, slow braking down a hill. The drum traps heat and dust inside itself, unlike a disc which cools through the air, so dragging the pedal for kilometres down Vlasic or Manjaca can completely glaze the shoes and destroy them in a single trip. Learn to brake in measured, shorter but firmer pulses, instead of resting your foot on the pedal for kilometres at a time.
The drum itself has the maximum allowed inner diameter stamped on it, usually on the outside, for example 200.9 mm for a nominal 200 mm drum. When a mechanic measures with a micrometer and finds it has crossed that limit, the drum gets replaced. Machining drums on a lathe is no longer routine on modern thin drums, because the wall becomes too thin to safely carry the load.
Wheel cylinder failure, leaks, seizing and one hot wheel
The most common quiet failure we see on drum brakes is not shoe wear but a leaking wheel cylinder, the working cylinder that uses brake fluid pressure to push the shoes out against the drum. Over time the seals inside the cylinder give way, fluid starts to weep, and when we open the drum, everything inside is soaked. The shoes get contaminated, lose their coefficient of friction and stop biting, even though they still look like they have plenty of material left.
The other failure mode of the cylinder is seizing, when the piston gets stuck in the extended position. The shoe then stays pressed against the drum even after you release the pedal, which shows up as one very hot wheel after a short drive. Put your hand near the rim after a couple of kilometres. If only one side is hot and the other is cold, you are very likely looking at a seized cylinder.
That is why the fix is never just swapping the shoes. If the shoes are soaked with fluid, you have to deal with the source as well, meaning the cylinder itself or at least its seal kit, and the return springs which often give up after years of working under heat.
How the handbrake reveals the condition of the rear brakes
The handbrake is your best diagnostic tool for the rear drums, and most drivers do not use it that way. If the lever travels almost to the end of its range before the car stops on a slope, or does not hold at all, the first suspect is not the cable but the self-adjuster inside the drum. That is a small toothed mechanism that automatically compensates for shoe wear, moving them closer to the drum as the lining wears down.
On cars that rarely use the handbrake when parking, the self-adjuster rusts and stops working, so the shoes stay in the position they were in a couple of years ago. The cable then has to travel a huge distance to bring them close to the drum, which gives that deep and lifeless feel to the lever. The fix is cleaning and lubricating the self-adjuster during service, or replacing it if it is already permanently seized.
A practical tip that extends the life of the whole assembly. Use the handbrake every time you park the car, even on level ground. The motion of pulling and releasing the cable activates the self-adjuster and forces the mechanism to work, which keeps it alive and clean far longer than it stays on cars that rely on first gear alone.
When to come in and what gets replaced as a set
A vehicle with faulty rear brakes will not pass the technical inspection, because the rolling-road tester measures braking force per axle and the handbrake has to show enough force on the rear. So do not wait for the inspection to find the problem, especially if you are noticing any of the symptoms above.
Once a drum is opened, it always gets serviced as a set across the axle, on both wheels. That means both shoes left and right, the return springs, the seal kits inside the cylinder or the whole cylinder if it has already leaked, and possibly the drum itself if it has gone past the maximum diameter or has cracked. The reason for replacing in pairs is simple. New shoes on one side and worn shoes on the other give uneven braking, which brings the pulling to one side right back.
If you are not sure what condition your rear brakes are in, book an appointment and we will open the drum on the spot. Better to check now than to find out on the inspection lane or, worse still, on a slope.