Drum Brakes Inspection & Service First you must get the drum off! • Some slide right off, • Some have to be hit with a hammer. • Some have holes to install two bolts (Tighten each bolt equally) Remove A Brake Drum Use penetrant around axle hub May need to hammer floating drum Wet down inside of drum to control dust before hammering Only hammer on the axle flange! (ask to be shown) May need to adjust brake shoes inward Remove A Brake Drum For a fixed brake drum you will need to carefully adjust the wheel bearings when done! There are many tricks to removing stuck brake drums. Before you break something ASK! Understand each piece and avoid mistakes Terminology Anchor Wheel Cylinder Brake Shoes Primary Secondary Return Springs Shoe hold downs Terminology Parking Brake Strut Parking Brake Cable Self Adjusters Backing Plate (often neglected) Backing Plates Backing plates are often overlooked and usually have grooved & worn shoe support pads Be sure to thoroughly clean backing plate and lightly lube the support pads • contact points on backing plate are called a shoe pad. They should be filed flat to prevent shoes from hanging up in deep grooves or better yet just replace the backing plate. Always lube Shoe Support Tabs with a thin layer of Synthetic Disc Brake Lubricant (or suitable lube) Be careful… do not use too much. Grease on brake shoes is BIG TROUBLE! Dual-Servo or Leading-Trailing • Drum brakes on Rear Wheel drive are most often Dual Servo. • They have a Primary and Secondary brake shoe • The Primary shoe friction material is shorter and it faces the front of the vehicle Dual Servo braking action Both brake shoes will pivot Primary shoe will wedge the secondary out into the drum Primary and secondary shoe will fit backwards, but not properly work Which is the primary shoe? Where is the front of this vehicle? Dual-Servo or Leading-Trailing • Drum brakes on Front Wheel drive are most often Leading-Trailing. • They do not have Primary or Secondary brake shoe • Less effective for stopping power but less likely to lock up on heavy braking Leading-Trailing Leading-Trailing There are MANY variations in drum brake design • Springs must be in proper location • Clips and self-adjusters are not always obvious as to how they fit • ALWAYS take a picture first, or repair one side before starting the other Brake Inspection Machine or replace drums with any visible wear Most require .030” smaller than discard diameter, after machining Drum diameter must be within .020” from other side to prevent pulling brakes Use a brake drum micrometer Convert Inches to Millimeters Many brake drums specify diameter in millimeters. Multiply inches by 25.4 to get millimeters After machining you measure a drum at 7.890” - How many mm? Figure this now! Convert Inches to Millimeters 7.890” X 25.4 = ? 200.406 mm The drum is stamped “MAX DIA 201mm” - Can you use this drum?? .030” X 25.4 = ? 0.762mm Is this drum O.K. to use? 200.406mm + 0.762 = 201.168 REPLACE THIS DRUM! Brake Inspection Inspect rear axle oil seals ANY oil leaks will ruin new brakes Oil on brake linings will cause brakes to grab or pull Brake shoes contaminated with oil or brake fluid must be replaced Reline Drum Brakes Best to replace wheel cylinders Wheel cylinders often begin to leak after new brake shoes are installed Leaking wheel cylinder will cause? Spongy or low brake pedal Contaminated Brake linings that GRAB Brake shoes wet with brake fluid must be replaced Reline Drum Brakes Clean backing plate BEFORE removing wheel cylinder (This keeps open brake line free from dirt) Remember to flatten & lube Shoe support pads Location of wheel cylinder and open hydraulic brake line Prevent Brake Fluid from leaking out of brake lines! • Once brake fluid has run out of the brake line it can be VERY difficult to get rid of trapped air! Always HOLD brake pedal ON (blocks vent port in master cylinder) This will hold brake fluid inside the open brake lines Replace springs & Hardware if any signs of overheating, rust, damage Free & loosen parking brake adjustment Ensure park brake cables do not bind Free & Lubricate Ensure park brake cables do not bind While the brake shoes are off, pull cable to ensure it freely slides IN and OUT of cable housing Sticking cables should be replaced! Cables have a liner that wears out and allows corrosion that can not be fixed Free & loosen parking brake adjustment Ensure park brake cables do not bind Reline Drum Brakes Keep the new linings CLEAN Best to put masking or painters tape on lining BEFORE handling brake shoes Use brake clean on small grease spots Learn to use the proper tools for removing and installing brake springs & hold downs Brake adjustment is Critical! • Modern drum brakes are self-adjusting • Adjuster mechanisms often stretch, corrode, and quit working • Always clean & lube self adjusters Brake adjustment is Critical! • Some will adjust only when backing up • Some adjust only with parking brake Self adjusters work BACKWARDS when installed on the wrong side Repairing ONE side at a time avoids this problem Brake adjustment is Critical! • A poorly adjusted brake can cause the brakes to grab • A poorly adjusted service brake will cause the parking brake to have too much travel • Always pre-adjust brakes when installing new brake shoes Brake Adjustment • Use a brake caliper to start • If new shoes will not adjust down small enough for the new brake drum, loosen the parking brake cables • sometimes people tighten the parking brake before they check the adjustment of the service brakes • Properly adjusted new brakes will slightly drag on the drum Brake Adjustment • After adjusting service brakes…. • Adjust parking brakes • Must fully apply at about ½ of park brake pedal - lever travel Test Drive and Burnish Brakes Complete several stops from 30 mph • Use moderate braking pressure & allow time for brakes to cool between stops • Use parking brakes and perform several stops in reverse • Advise customer to use brakes gently while new brakes are “burnished” or fully seated.