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Currently I own a Mk5 Astra SRi, however I am looking to sell this and buy a Ford Focus Mk2.

The other day I looked at a Ford Focus Zetec Mk2. My understanding is that Zetec is sort of the ford equivalent of an Astra SRi (given that ST is the equivalent of a VXR).

The only thing that really threw a spanner in the works for me was the drum brakes on the back wheels. I had a look around and found that the latest two models of VW Polo have discs, as do Golf's from Mk4 onwards, as do most Seat Leons, and even Prius's!

Why on earth would a reputable company still fit this ancient technology, when most modern cars are using rear disc brakes? And, how much of an impact do drum brakes have in comparison to disc brakes?

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6 Answers 6

up vote 8 down vote accepted

Drum brakes are cheaper to manufacture than disc brakes, because there are fewer moving parts and because in the rear the parking brake (which often works by a drum-and-shoe mechanism even on four-wheel-disc-equipped cars) can share a drum with the "regular" brakes.

All other things being equal, discs work better than drums, especially in wet conditions.

However, in this case, in regular driving you will very likely never notice a difference. Most of the braking effort, even in a panic stop, comes from the front wheels. So front discs are much better than front drums, but rear drums are not much worse than rear discs.

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4  
for what it's worth, plenty of disc-brake-equipped cars do not use drum parking brakes. –  mac Jun 18 '13 at 18:09
    
@mac: Good point. The only cars I've seen like that are '80s Saabs, but I can believe there are others. Edited my answer. –  dodgethesteamroller Jun 18 '13 at 18:44
    
Adding on to this - the braking percentages are something on the order of 70Front/30Rear or 80Front/20Rear in some cases. –  jsanc623 Jun 18 '13 at 21:14
    
More examples. 2g Mitsubishi Eclipse uses drum in disc setup for parking brake. MKII MR2 uses a special disc only parking brake mechanism. –  Brian Knoblauch Jun 20 '13 at 18:45
    
BMW 318 TDS E36 (1996) Compact has rear drum brakes –  Skippy Fastol Feb 4 '14 at 16:35

Tom & Ray point out that drum brakes can serve double-duty as the parking brake. Other people around the web believe it has to do with retooling costs.

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The rear brakes hardly contribute to stopping your car. They do between 20% and 30% of the work, so they can be cheap without compromising your safety or stopping distance. Mind you, drum brakes last much MUCH longer than discs. I have a Vauxhall Corsa B that has done 100k miles (160k kilometers) and the drums and shoes are still good for at least another 50% of that distance. See it as Ford saving you money. If you want to increase your braking performance, spend some extra money on pads and rotors up front the next time you have to change them. And stay away from slotted and cross-drilled rotors if you don't do lots of high speed stops. A smooth rotor has a larger contact area, so gives better stopping performance in normal conditions. Slotted and drilled rotors are a compromise between performance and better cooling characteristics for sport and track applications.

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"Slotted and drilled rotors are a compromise between ..." - they're not really a compromise when you take in to account the full set up of much larger pads and rotors. Interesting point nonetheless. –  andrewb Oct 5 '13 at 23:34
    
Understood. But your average ricer doesn't go for larger rotors or pads, they just have the OEM stuff drilled, which is stupid. –  Juann Strauss Oct 7 '13 at 10:21
    
They also have better performance in wet conditions, as they prevent hydroplaning ? correct me if i'm wrong –  chilljeet Feb 16 at 11:11

Besides being cheap to manufacture, lighter, being easier to use as a parking brake, and being of limited usefulness on a front engine car to begin with... Drum brakes also have the advantage of being "no drag". When they're off, they're completely off. Compare to disc brakes where there can still be a little bit of drag as there's no mechanism to pull the pads off the disc when not under braking...

It's a common thing for drag race cars that come with disc brakes to have them removed and replaced with drums for the weight and drag reasons.

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Drum brake using smooth driving stop & load based vehicle must used drum brake.working parts are simple mechanisum.

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I'm going to assume English isn't your first language, but was wondering if you could clarify what you are trying to say here? You are saying that drum brakes are smoother than disk? And that load based vehicles must use drum brakes? Maybe elaborate why you think this? And the last part the working parts are simple mechanisms? Am I on target here? –  Paulster2 Feb 14 at 17:01

Because it's cheaper to produce. And that may not be so bad since it's cheaper for you as well, to maintain at least.
They are also smaller in dia (not width necessarily) for the same braking force when compared to discs. This is due to the fact that the entire surface of the brake pads press against (and at) the circumference (in an axial direction). If you have alloy wheels and brakes are visible, then they might look a tad bit tiny compared to a similar class car employing disc brakes. So , if you're looking for street creds.. painting them red may not really..
Since the pads press against the drum shoe in an axial direction, they have a tendency to stick on/force the pads into full contact. This effect reduces the need for brake assist mechanisms, especially on smaller cars where it can be done away with (again, a plus for the manufacturer). Consequently, this effect, which affects the response time, could possibly be one reason why their use with ABS and similar systems is rare.
Drum brakes do not dissipate heat as well as disc brakes (open and exposed) which quite simply is its biggest disadvantage over disc brakes. This precludes its use from performance applications, though, there are exceptions.
As other answers have pointed out, this may not necessarily effect you in emergency braking situations as most of the weight shifts towards the front of the vehicle and hence most of the braking is done by the front brakes (discs in your case). This, of course is assuming that the car is pointed in the direction of travel. High speed pursuits/get-aways in reverse gear might require a different setup (fast and the furious. anyone?)
Some clarifications -
Drum brakes do, in fact, have more moving parts than disc brakes, and do have a more complicated mechanism .
Can be adapted easily for mechanical/cable linkages , making their use popular for parking/emergency brakes

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