Curing brake-squeal complaints

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Curing brake-squeal complaints Powered By Docstoc
                                                                                                              By Dave Cappert

     Curing brake-squeal complaints
        f you perform brake work, squeal problems are some-         for lubricating the caliper mounting slides. Since you don’t
        thing you’d like to avoid at any cost. Although brake       routinely repack front bearings on front-wheel-drive cars,
        squeal causes more brake-job comebacks than any             make sure to periodically clean and lubricate the slides
     other type of service, you can prevent most of them if you     and hardware.
     recognize the major causes. Here’s a countdown of the
     top-10 brake-squeal factors. Get to know them well; your       Rotor/drum defects
     reputation rides on it.                                        Roughness, scoring, hot spots, out-of-square, out-of-round
                                                                    or bell-mouth conditions are the things to look for. Scoring
     Missing/damaged disc pad insulators                            occurs when sand or grit gets between the lining and
     Even with a securely mounted pad, squeal can result            the rotor or drum, when the lining is of poor quality or
     without a good insulator shim. It’s especially important       has excessive wear. Before machining rotors and drums,
     on imports, because both inboard and outboard pads may         make sure the lathe’s cutting bits are sharp. Check the
     use an insulator shim. Check the pad closely to make sure      lathe’s cutting depth, speed and feed for proper setting.
     it’s insulated properly. If the shim looks damaged in any      Use a dampening device during machining to prevent a
     way or is missing, install a new one.                          chatter-related rough finish. After machining, use a lathe
                                                                    swirl grinder or sand in a circular motion with a piece of
     Loose pad-to-caliper fit                                       No. 120 emery cloth.
     A loose outer pad can vibrate at high frequency against
     the caliper housing, producing brake squeal. Although          Improper drum/shoe contact
     measures to ensure a snug outer pad are no secret, there are   Lining pinch is one of the most frequent causes of squeal
     several ways to get the job done. Since methods can vary       on drum brakes. This occurs when the heel and toe of the
     for the same manufacturer because of different calipers,       shoe push against the drum, but the center doesn’t. Today,
     the best thing to do is follow the procedure that applies      most brake shoes come with lining that has an eccentric
     to the brake system you’re working on.                         grind, rather than a concentric grind, right off the shelf.
                                                                    This means the lining is thickest at the middle of the shoe
     Rusty, burred or worn caliper slides                           and tapers towards the heel and toe. Eventually, the lining
     This results from a lack of lubrication between the caliper    will wear in and match the diameter of the drum.
     and the caliper mounting. On vehicles that get a liberal
     seasoning of salt during winter, this lubrication is even      Defective lining
     more crucial. Follow the manufacturer’s recommendations        Look for wear, grease, glazing, dirt and loose rivets or

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22     ■   August 2009
bonding. If there are signs of damage, replace the shoes or                             squeal. This spring looks a lot like those used on screen
pads in axle sets. On some vehicles, brake squeal may be                                doors. Don’t rely on comparing the other drum to see if its
loudest when the brakes are applied for the first time in                               spring is in place. It cou
Description: Reputable brake manufacturers go through costly, painstaking processes to make sure their brake shoes are OK, but there's always the possibility of shoe damage during shipping and handling. If the lining looks like it has the proper eccentric grind, look down the ends of the shoes while holding something known to be square against the spot where the webbing joins the metal backing for the lining. Check both ends and both sides of each shoe.
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