Close up of the wheels on one side of a car

Explained: How Do Drum Brakes Work?

For the vast majority of drivers, the most they know about their brakes is that they put their foot down on a pedal and the car slows down as a result. 

What are drum brakes?

Braking systems can be found in one of two ways, either a disc or a drum. Disc brakes are the easiest type of brake to spot from a distance – particularly if the car is fitted with a bright red Brembo pad – whereas a drum isn’t as noticeable from afar. Instead of the car being slowed down by pads pressing against a disc as is the case with disc brakes, drum brakes operate with a brake drum within the wheel. In fact, drum brakes were the first type of brake to be fitted within the wheel itself, first seen on a Maybach but patented in 1900 by French inventor Louis Renault, who co-founded the manufacturer which bears his name alongside his two brothers a year earlier.

How do drum brakes work?

Drum brakes are made up of a system containing hydraulic wheel cylinders, brake shoes and a brake drum, hence the name. When you press down on the brake pedal, the two brake shoes are pushed against the inside of the drum and the friction material lining the shoes generates the required force to slow the car down to a stop.

Do drum brakes have pads?

There are no pads on a drum brake system, instead they use something called a brake shoe. To the uneducated eye, and at a very brief glance, brake shoes can look similar to brake pads, and they do provide a similar service within the brakes themselves. However, if you’ve been told you need new pads, then you will not be running a drum brake system, and instead will be using brake discs.

Do drum brakes last longer than disc brakes?

The brake shoes found in a drum brake have a larger contact patch than you’ll find on a brake pad in a disc system, which means that, generally speaking, it will take longer for them to wear down to the point where you need to replace them. However, while they may last longer in the long run, when it comes to actual braking ability, you are more likely to overheat a drum brake than you are a disc brake, meaning in short bursts, disc brakes actually last longer in terms of performance. 

The reason for the lack of performance on drum brakes is due to all of the components being housed within the metal cylinder of a brake drum, which retains the majority of the heat generated under braking. The more heat there is, the less friction can be applied, and the less friction that can be applied means that your brake pedal will suddenly feel a lot less responsive, commonly known as ‘brake fade’. Even though modern technologies have vastly improved the drum brake since Louis Renault’s first attempt 120 years ago, the overarching design flaws still remain, and you’re only ever likely to find drum brakes fitted to the rear axles.

While the substantial flaws in the way drum brakes operate has seen them phased out in favour of disc brakes, particularly on front wheels, they remain on almost all cars in the form of the handbrake (parking brake). Disc brakes shrink and expand as the temperatures drop and rise respectively, meaning if a car was fitted with a disc brake as a parking brake and left on a hill overnight, as the temperature dropped the brake would lose contact and you’d wake up to find your car had rolled all the way down to the bottom, unless it had found something else in the way first.

Do drum brakes need to be replaced?

It is advised for brake discs to be changed every 80,000 miles or so, but if you’re running with drum brakes you’ll be pleased to know that they last considerably longer before you’ll need to replace them. The shoes are likely to need checking a little more regularly, but the brake drums themselves can last between 150,000 to 200,000 miles. Regularly maintaining brakes will ensure that they’re kept in top condition and elongate their usable life, so it’s important to keep up with your car’s service schedule.

How long does it take to replace drum brakes?

If you do get to the point where your drums now need replacing, then luckily for you it’s not going to be a mammoth job, providing you leave it to the professionals. Left in the capable hands of a garage and qualified mechanics, and assuming that you have no other major work that needs doing, it should take no more than two hours – plenty of time for you to drop the car off at the garage, walk into town, browse a few shops, have a coffee and slice of cake and slowly wander back to pick your car up.

How to adjust parking brake on drum brakes

  1. Lift the vehicle

First off, ensure that your car is parked on a level, flat, surface and jack it up. Always hold the car up with jack stands, as jacks themselves are not designed to support the weight of a car on their own for long periods of time and you could risk serious injury of the car falling on top of you.

  1. Relax the brake cables

Once under the car, locate the brake cable adjuster, which is usually either pretty much halfway between the front and the rear, or connected to the parking brake lever.  After you’ve found the adjuster you’ll want to turn it anti-clockwise to provide some slack in the system – although it’s worth checking your user’s manual to ensure that this is correct for your specific model. Do not slacken it off entirely so it becomes loose, but just enough so they’re not pulling on the rear shoe adjuster. If you fail to do this you may not be able to make the adjustments correctly.

  1. Adjust parking brake shoes

In some cases you may need to remove the wheel in order to access the star adjuster, which can sometimes be accessible through a hole in the back of the drum backplate. Double check which side of the car you’re working on and turn the adjuster in the correct direction, referring to the owners’ manual if you get stuck. You’ll need a flathead screwdriver – or a tool called a brake spoon, which has bends to allow you to reach star adjusters in tricky locations – and will only need to turn the adjuster a few clicks. Once you’ve shortened the adjuster, reinstall the brake drum, and double check to ensure that the brake shoes are centred within the drum itself. When reinstalled, turn the drum and listen out for the rubbing sound. The sound should be consistent and the drum should turn without any resistance. Keep expanding the adjuster and centering the shoes until you have reached the correct shoe-to-drum pressure.

  1. Adjust parking brake cables

With the wheels reinstalled, now begin to tighten the cable adjuster that was loosened at the very start of the process, although only do this a little at a time as you don’t want to overtighten the cable and cause the shoes to drag within the drum. Once tightened, pull on the handbrake to engage the shoes, the level should firmly stop about halfway through its available travel. If the lever pulls up much higher than expected, you’ll need to turn the cable adjuster more.

Now, with the brake engaged, attempt to turn the wheels. If you can turn them, then the cables aren’t tight enough and the brake won’t hold your car in place. Again, just be aware that overtightening can also cause more problems with dragging brakes. Now release the brake, lower the car down off the jack stands and go out for a quick test drive.

How to change rear drum brake

  1. Remove the wheel

Before you get started with anything, loosen the wheel nuts on the wheel(s) that you’ll be making the changes to. Then, as with all tasks that require getting underneath the car, make sure you’re on a level, flat surface and jack the car up. Again, always ensure that the car is held up by jack stands and never by simply the jack itself. Once up in the air, remove the wheels. If you’re working on the rear axle (which is likely given you’re working on drum brakes), then you’ll need to make sure you’ve secured the front wheels, either by chocks or wooden blocks, as the handbrake won’t work with the rear wheels in the air.

  1. Remove brake drum

Removing the brake drum can usually be achieved by simply moving it back and forth while pulling away from the hub. If it seems to be stuck, then double check that the handbrake is disengaged as this will lock the brake drums if it’s set. On some vehicles you may find the drum held on with screws, so have a screwdriver to hand just in case.

  1. Clean brake mechanism

Once you’ve managed to remove the drum, the brake assembly will now be exposed, giving you a great opportunity to give it a thorough clean. Place an oil drip tray underneath the brake assembly and spray brake cleaner meticulously throughout the system. Cleaning is an important part of the process, as a build up of brake dust inside the drum can cause more problems down the line such as uneven brake wear and noises or vibrations from the brakes.

Remember: Always wear a mask when cleaning or working on brakes. Although asbestos has not been used in brake manufacturing for many years, brake dust itself can still be very harmful if inhaled. 

  1. Inspect brakes

Once everything has been cleaned, before you start replacing parts you should take the opportunity to inspect the components sitting within your brake drum. 

  • Brake Shoes – Using a digital micrometer, you can measure the old shoes and if you notice they’re under 1.6mm, then it’s time to replace them.
  • Brake Drums – Check for scoring, cracking or grooving.
  1. Dismantle the brake

Now there’s a long list of pieces to take apart, in a specific order. First off remove the brake shoe retaining springs using a set of needle-nose pliers. There are often multiple sets of springs, so the best practice is often to remove the top spring first, as this will loosen the overall tension and make it easier to remove the remaining springs.

Once the retaining springs are off now you can remove the brake drum shoes. These are often secured with pins and washers, so using your needle-nose pliers again, remove any pins and washers and remove the shoes.

With the parts removed, you now have a great opportunity to inspect your wheel cylinders for any fluid leaks. Any leaking at this point would suggest that there is a brake fluid leak, and that would compromise not only the efficiency of your braking system, but also the safety of the car in general. If you find any then replace the cylinders as soon as possible.

Finally, remove the parking brake cable retainer clip. This can be done by either prying it with a flathead screwdriver or twisting with your pliers. Be sure to check your new brake shoes to check if they come with a new clip or not, as if they don’t you will need to be able to keep the clip somewhere safe to be reused when the new shoes are installed.

  1. Install new brake drums and shoes

Now everything is out of your way, take the opportunity to clean the backing plate with brake cleaner. Again, a build up of brake dust could cause problems in the long run so give it a thorough clean. Once it’s cleaned, apply lubricant to the relevant areas, including the anchor of the pin and parking brake actuating lever pivot surface. 

The reinstallation process, unsurprisingly, follows the removal process timeline, just in reverse. To reinstall the parking brake lever and retaining clip, slide the pin through the new shoe and replace the clip, remember you may need to find the old clip if the new shoe doesn’t come with one, and then install the adjusting screw assembly and spring.

Place the new shoes onto the hub, and secure them in place with the pins and washers that should have come with the drum brake kit. If your kit also comes with a new adjuster component (found at the bottom of the brake shoes), replace this as well.

Replace the tensioning springs, again in the reverse order to that you removed them in at the start of the process – so go from the bottom up to the top this time. Once these are back in place that should now mean the entire brake assembly is now reassembled, so you can now install the hold down pins and springs of the drum assembly, and then the return springs by attaching the spring to its correct location.

  1. Adjust brakes so shoes expand

Using a screwdriver, or dedicated brake spoon, adjust the brake shoes until the drum can only barely be turned by hand. Now back off the adjusting screw a few notches so that there is no dragging. Set your torque wrench to the desired reading and turn it until it clicks – the correct torque specification is found in the owner’s manual.

  1. Install the new brake drum

Most drums will come coated in a thin oily film to prevent them from rust during the shipping process, so make sure to coat it in brake cleaner to remove any of the film that may remain before installation. Then slip it over the shoes and install it on the hub. If you encounter any problems, you may need to adjust the shoes so that it can be fitted correctly.

Once in place, you should make a final adjustment to ensure everything is in the right place and sitting correctly – ill-fitting shoes may not work correctly, and could also cause problems with the parking brake if too loose, while you could find overheating and unwanted damage to the drums and shoes if they’re too tight.

  1. Reinstall wheel

Put the wheel back onto the car, and tighten the wheel nuts – but not all the way while the car is still in the air. Carefully lower the car back down off the jack stands, then when it is back on the ground, tighten the wheel nuts to the correct specification for your car.

  1. Test drive

Give the brakes a pump of the pedal to distribute hydraulic pressure into the system and check that the handbrake is also working correctly and not feeling too loose. A short test drive should give you the information you need to be able to tell if your brakes have been replaced and installed correctly.

If you discover any issues, such as the pedal feels loose or hard to push, then stop as soon as it is safe to do so and make adjustments, or alternatively have the brakes inspected by a professional mechanic at the nearest garage.

How to keep drum brakes from rusting

The difficulties with brake drums is that, being made up almost entirely of metallic parts held within a metallic house, rust is simply a hazard that can be hard to get away from. To try and avoid as much of the rust as you can, when you’ve got the wheel off to carry out maintenance or replace your brake drums (as above), remove all of the rust and clean the drums thoroughly with brake cleaner, and then paint the inside of the drum with anti-rust spray paint.

If you’ve been having issues with your brakes, or perhaps have attempted to repair them yourself and have simply made things worse, then it may be time for you to send the car off on one final one-way journey to the scrapyard. Selling your car as scrap or salvage with Scrap Car Comparison is not only the simplest option, but will also guarantee you an unbeatable quote. No matter where you are in the country, we’ll come and collect it for no additional cost. Jump online today and find out just how much you could receive for your old car and let Scrap Car Comparison handle the rest.

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