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 www.pten.com ■ 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