Adjusting Drum Brakes

All you need to know about drum brakes

Although drum brakes are being phased out of newer vehicles, they are still widely used in many popular older makes and models of 4WD. Drum brakes are made up of brake shoes, wheel cylinders, retaining clips, springs, adjusters and in some models, handbrake levers and cables.
When putting your foot on the brake pedal, brake fluid passes from the brake master cylinder to the wheel cylinders. The wheel cylinders push the brake shoes outwards, where they contact the brake drum. The rotation of the brake drum forces the brake shoes into itself, jamming the shoes harder into the drum and stopping the vehicle.
An improperly adjusted brake drum setup can cause long travel in the brake pedal, pulling the vehicle to either side of the road, as one side brake contacts before the other side. Brake drum set-ups are really simple in operation and very easy to adjust.

The rear disk rotor retup incorporating the handbrake inside the disk rotor.


The rear disk rotor retup incorporating the handbrake inside the disk rotor.


REMOVING STUBBORN BRAKE DRUMS

Removing the brake drums can be difficult, especially in 4WDs which may have been dunked into water on numerous occasions. Sometimes when you remove the wheels the drums will come straight off, but sometimes a quick hit with a hammer on the face of the drum is necessary to release it from the axle hub.
Some manufacturers have actually made drums with bolt threads in them, so if they are really stubborn you can give them a quick spray with CRC and screw a bolt in either thread. Screw them in evenly and the brake drum should come right off.
If you’re having trouble removing the drum, check you haven’t accidentally left the hand brake on, as this will obviously hold the brake drum on. Even though this sounds simple, it’s a very common mistake.

 The manufacturer has fitted screw threads so the rotors can be removed without damage.


The rear disk rotor retup incorporating the handbrake inside the disk rotor.

 Adjusting the handbrake with a flat blade screwdriver through the hole in the rotor.


The rear disk rotor retup incorporating the handbrake inside the disk rotor.


QUICK CHECKS
When you are checking and servicing a rear brake system you will need to carry out a number of quick checks. The brake shoes themselves have a brake lining and that lining will have a minimum thickness. If the brake shoes are less than 1mm, it’s time to replace them.
The wheel cylinders are the hydraulic components to the rear brake system. They have rubber dust boots covering their sides. Internally, the wheel cylinders have some basic cup seals, which will need to be checked for leaks. By pulling back the dust boots slightly, you can see if there is any brake fluid visible. If brake fluid is visible then the wheel cylinder is leaking and will need to be replaced. Wheel cylinders are always replaced in pairs.
The brake springs, clips and retainers will need to be checked for cracks or damage and the brake adjuster will need to be checked to make sure it is free and not seized.


ADJUSTING THE BRAKE SHOES
Also check the inside of the brake drums for wear. If all the checks are ok, then the brake shoe set up will need to be adjusted. Adjusting the brakes is all about decreasing the size of the gap between the brake shoes and the brake drum, so that when the brake pedal is pressed the brake shoe only travels a short distance to contact the brake drum.
Some brake drums have a backing plate with a cut out in the rear, which allows you to turn the brake adjuster, pushing the brake shoes closer to the drum. Others require you to remove the wheel and the brake drum and manipulate the adjuster slowly.
Brake ShoesThe brake adjuster is on a screw thread so when you turn it out it will push the brake shoes closer to the drum. The adjuster can be reached through the backing plate of the brake set up and turned with either a screwdriver or a brake-adjusting tool that is designed for the purpose.
Adjusting the brakes through the rear of the backing plate, you turn the adjuster until the brake shoes contact the drum and begin to grip. Once you feel the shoes grip tight you will need to the turn back the adjuster in the opposite direction until you are able to turn the brake drum freely.
Before you attempt to adjust the brakes in this way, you will need to remove the brake drum and take a good look at the adjuster as they are designed with a locking ratchet so the adjuster cannot undo itself. You will find the adjuster will turn easily when adjusting the brakes up, but the locking ratchet will need to be released in order to back off the brake adjuster. This can be done simply by pushing a small flat screwdriver through the hole in the backing plate and lifting the locking ratchet from its position. While holding the locking ratchet up you will then find you will be able to back off, or release the adjuster.
As mentioned above, some brake set-ups have a hole in the backing plate for adjusting and others don’t. If there isn’t a hole in the backing plate for adjusting, then the brake drum will need to be removed and you can access the adjuster from the front. You will be able to turn the adjuster and refit the brake drum to see how much tighter the adjustment is. Brakes that are adjusted correctly should have very slight drag when the brake drum is rotated.
Drum brakes are also used in camper trailers and can usually be adjusted in the same manner. Some do have snail cam adjusters which are just a different type of adjuster. They are very simple in operation and are usually adjusted with the brake drum in place. The snail cam adjusters are turned from a bolt on the rear of the backing plate, and are simply turned until they lock the brake drum and then just loosened off until the brake drum turns freely.
If you are going to attempt to replace your rear brake shoe set up by yourself, there is a bit more you should know before you do so. The brake shoes have a leading and trailing shoe which will need to be fitted correctly. Replacing wheel cylinders requires bleeding of the brake system and springs, and the retaining clips and adjusters all need to be reassembled in their correct positions or the brakes may not work correctly. It is important to be aware of these things before attempting to adjust your brake system and if you’re not confident in your ability you should get a professional to replace the brakes for you.

Travel safe and GO NUTS!


Qualified motor mechanic Adam Adler has spent half his life under the bonnet of a 4WD and has worked for some of the top accessory companies and workshops. He knows what it takes to get your vehicle out there and back home in one piece. He runs the online aftermarket store www.nutsabout4wd.com.au.


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