Undercar - Service Repair

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Checking the stoppers

Your customers have to be able to trust the left pedal, so they put a lot of trust in you.
Thursday, June 20, 2013 - 12:30
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These, along with the tires they’re connected to, are responsible for bringing a 3,000-plus pound vehicle from road speed to a stop over and over for thousands of miles.  The middle photo is a rotor with its cooling fins packed full of mud.  The right hand picture is what happens when the pads grind the rotors thin enough that the piston comes out of its bore.  Scary stuff.

A friend of mine was driving his high mileage Toyota Camry a few years back and experienced normal stops right up to the point where one brake pad finally wore thin enough that it left its perch in the caliper and shot out of there without warning. His pedal went to the floor and he had to swerve off of the yield lane over onto the grass to avoid driving under the side of a passing semi trailer.  It happened because the Camry’s rotors had been repeatedly machined but not measured too many times (I did not do this work, by the way). The moral of that story is to always measure the thickness of the rotors and the diameter of the drums when doing the brakes, even if they look good. And it’s a no-brainer that we should replace the rotors rather than machining them if they’re too thin.

Every driver desperately needs to be able to trust that left pedal. The old adage that “a miss is as good as a mile” might make some brake failure stories humorous, but brake failure is no laughing matter, and there are many other stories involving failed brakes that are life-changing in a very bad way.

Iron, Steel and Linings
Drum brakes are still very common and require more inspection effort than discs, particularly when the shoes have dished the inside of the drum and/or the drum is rusted solidly to the hub. Most foreign nameplates have 8-mm threaded holes near the center of the drum where bolts can be screwed in against the hub flange for drum removal. A smart tech working an unfamiliar platform will leave the drum brakes on one side assembled for comparison while doing the opposite one. When machining drums, measure them first for service limit and don’t let the drum pass the bit too fast or you can thread the drum while machining it and cause noise concerns.

It is always amazing how much punishment and neglect brakes can put up with and still stop the vehicle in a fairly normal fashion. It’s also amazing how some folks are at doing those grass-and-dirt patch jobs (see right).

Those drum-style parking brakes that are in the rotor hat on newer Chevy pick-ups usually are worn out and are easy to replace while doing the rear disc pads. On the ball-and-ramp park brakes used on some rear disc systems, you need the tools to screw that rear caliper piston back in rather than simply shoving it, so don’t get blind-sided on that deal. If the park brake cables are rusty and cause the brakes not to release, those cables might need to be replaced. This happens sometimes on older pick-ups.

If we’re doing any service at all on a vehicle and we’ve got it on the lift, we’re remiss if we don’t at least bust out a flashlight and have a look at the disc brakes, both front and rear. Disc brakes usually feel just fine, but we’ve all heard them make noise when the lining gets thin enough that the sensor reed begins to sing against the rotor. A few platforms have pads with an imbedded wire that illuminates a dash panel warning light when the lining is worn to replacement thickness. And be sure to check both pads on each rotor; a caliper that won’t float sometimes will wear the pad completely out on the piston side while leaving the outboard pad looking really good. When pad lining exhibits wedge-shaped wear, that means one end of the caliper is hung and won’t float. Replacing the bolts and boots on calipers that have that hardware is a must if those parts are compromised, and make sure the caliper abutments are clean, rust-free and lubed on the older ones that ride in slides.

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