How do you check brake shoe wear on the rear drum brakes of a Subaru Legacy?

Answer 1

Since this procedure involves removing the brake drum, you may wish to consider wearing a face mask of some sort to avoid breathing in brake dust which is none too good for you! You should also buy a spray can of brake cleaner at a local hardware or auto parts store.

Chock the front wheels to prevent the car moving.

Release the hand brake and select neutral.

Jack up a rear corner or whole rear end of the car and place secure supports such as axles stands underneath. Remove the road wheel in the usual manner.

The brake drum is exposed and theoretically will just pull off - there are no other fixings! In practise, it is often tricky to remove since the brake shoes may bind a little. Try wiggling it rather than banging it. Certainly don't use any hammering other than gentle taps with a rubber-faced hammer. The brake drum is made of cast iron and can easily be cracked.

On some models, there are two threaded holes in the drum roughly concentric with the wheel studs. These are designed specifically to help drum removal - you just find two bolts (8mm) or screws to screw into these holes and they push against the hub. Since this is the same size bolt used to remove the front brake rotor, you may want to buy a pair, label them and set them aside for brake work. Again, take care not to crack the drum. Only very light torque should be applied to these screws. Alternate between the two screws for best results.

If no success, then look behind the brake assembly so that you are looking at the back plate which the brake cylinder is mounted on. On some models, there is a little cover which can be removed to expose an adjuster. Turn the adjuster with the end of a small screwdriver in a kind of ratchet action. This will loosen the brake shoes away from the drum provided you move it in the right direction. So if it tightens, try the other direction! Remember to replace the cover afterwards. Now the drum should come away and you can inspect the shoes for wear. The lining thickness starts at a nominal 4.1mm (0.161 inches) and the lower limit for service is 1.5mm (0.059 inches).

It's a good idea to clean out all the brake dust (you are wearing that face mask, aren't you). It's best to use a spray can of brake cleaner, spraying all parts of the brakes, including the inside of the drum. That old vacuum cleaner that you kept when you bought a new one can be used for this job, making sure the exhaust is pointed outside away from you. Also check that the hand-brake and adjuster mechanisms are operating freely. Finally give a good look at the brake cylinder to check for any signs of leakage of brake fluid. If the outer dust seals are cracked, it's worth buying new ones provided that the pistons are still moving freely and there is no leak. The new seals will prevent you having to replace the entire cylinders so soon.

Finally, check the interior of the drums. There should not be any serious scoring. If you have a good internal caliper guage then measure the internal diameter of the drum on the wear surfaces. The high limit for service is 230.6mm (9.08 inches). Since it started life at 228.6mm (9 inches), not a lot of wear is permitted. Check in several places in case there is ovality (which can sometimes be detected by slight jerkiness when braking very gently at very low speeds on a smooth surface or by some types of brake judder).

IMPORTANT

When you have replaced the drum and wheel, operate the handbrake repeatedly to activate the auto adjustment. Keep doing it until no further change is detected in the position that the handbrake comes up to. This may be only one or two pulls if you didn't have to adjust anything when removing the drum to many tens of pulls if you backed off the whole adjuster (which you have to do if you fit new shoes, for instance.)

Test the service brake (foot brake) for the first time whilst the car is stationary with the engine running. Make sure there is the normal "feel" to the pedal. In other words, that it comes up firm and well off the floor! If not, don't drive until you have found the problem.

Finally, make a cautious test drive well way from traffic and other hazards if you can. This answer was written using UK terminology. Apologies if this causes any confusion for US readers!