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Second-rate parts mean second-rate results

When it comes to diagnosing a problem, one of the biggest mistakes is thinking that the problem is gone after you’ve installed a new part. I’ve had vehicles brought in countless times with the same old story attached to them. The customer will say:...

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GearWrench Launches Street Team, a New Mobile Driver Program

GearWrench, a premier hand tool brand from Apex Tool Group, has announced Street Team, a new program that gives independent mobile distributors the support of an established tool brand without the restrictions of a franchise. "Response to the program...

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AUTO 7 Named Approved Vendor For Automotive Parts Associates

Steven Kruss, president of Auto 7, which supplies Korean-made, OEM-quality automotive parts to distributors across North America, announced that Auto 7 has been named an approved vendor of Automotive Parts Associates (APA), one of the nation’s...

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Internal Engine Oil Consumption Diagnostics

Due to the variables in engine design and ­operating conditions, internal engine oil ­consumption complaints are often the most difficult to solve. In some cases, oil consumption might be more severe under low-speed operation, in other cases, high-speed...

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Hyundai Fuel System, Emissions Diagnostics

Hyundai has done a good job of improving its ­offerings over the years from both an aesthetic and mechanical viewpoint. Complemented by a strong warranty and good value, the carmaker has been able to increase its market share year over year. If you aren’t...

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Curing Volvo Manual Transmission Rattle

In an effort to increase fuel efficiency, today’s engines produce more torque so they can be ­driven at extremely low rpm. ­Reduced viscosity engine and gearbox oils, less vehicle weight and improved aerodynamics also contribute to better fuel economy....

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Talk To All Available Modules With Autel's MaxiDiag Elite MD802

Derived from Autel’s Professional Series tool, the MaxiDAS DS708, the MaxiDiag Elite MD802 enables the user to not only get into the OE enhanced OBD II system with mode 6 access and live data graphing, but it also allows a technician to scan the...

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Reflashing & Reprogramming Tools

In the first half of 2014, NHTSA has issued more than 15 recalls where the fix was to reflash a module on a vehicle. In the same time frame, more than 100 TSBs have also been issued where the solution is to reflash a module. These recalls and TSBs...

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Pulling Codes: An Advanced Misfire Story The Story of P0301

This article will document code P0301 — Misfire Activity on Cylinder No. 1 — a code many of you have run into, but sometimes we have case studies that are worthy of mention. Our subject vehicle is a 2007 Mercury Mountaineer. The vehicle has...

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The Why, Where, When of TPMS Sensors

To understand any TPMS relearn procedure, you have to understand this: Sensors only transmit, they do not receive. No vehicle asks a sensor for information on how it is doing. I know you’re thinking a sensor does receive signals when the vehicle...

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Most Common Causes of Misfire Codes

A flashing check engine light and a P0301 to P0312 diagnostic trouble code (DTC) is a surefire indication that one or more cylinders are misfiring. Occasional misfires may pass unnoticed, but a steady misfire is hard to miss. The engine usually feels...

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Pattern Failures of MAF and MAP Sensors

Pattern failures are those failures that happen over and over again — and the same applies to how customers describe these failures. Customers might unknowingly give you the answer to their problem without needing to open the hood. In this article,...

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Home Brakes Twin-Piston Calipers: Are Two Pistons Better than One?

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generate more torque. More torque means more stopping power. Also, by using the floating caliper design instead of an opposing piston design, engineers are able to avoid wheel clearance issues and other robust design features of the floating caliper.

With a single-piston caliper, the footprint of pad is limited in some ways to the diameter of the piston. The diameter can only grow so large in relation to the rotor and brake pads. If the pad is too long, it flexes. When the pad flexes, it creates an uneven friction coupling on the rotor’s face. The uneven friction can create unwanted noise. If the flexing is sever enough, the friction material can separate from the backing plate. An example of this is the early Chrysler Neon. Also, there is a direct relationship between the diameter of the rotor and the diameter of the single piston caliper.

With dual- or twin-piston brake pads, the pads can be larger with even pressure distribution. A larger brake pad has several benefits. First, a larger pad will absorb more initial heat (less thermal shock). Second, a larger brake pad will have better wear characteristics and a longer life due to even pressure distribution. Third, a larger pad is able to absorb more unwanted noise and vibration because it is able to cover more of the rotor.

Another advantage is in the area of drag and fuel savings. With dual- or twin pistons, it is possible to have more aggressive piston seals that can pull back the pads more effectively after the driver removes his foot from the brake pedal.

SERVICE CONSIDERATIONS
Dual-piston calipers can be serviced in the same manner as single-piston calipers with a few exceptions.

  • Look for uneven pad wear. If the pads have tapered wear, it could mean a problem with the caliper. Tapered wear could mean that the slides are binding or that one piston could be exhort more force than the other, or both conditions could be present.

    The slides and bushings play a critical role on dual-piston calipers. If there is too much play, the caliper could rotate on the slides. This will cause uneven pad wear.

  • The pistons on dual-piston calipers may be difficult to retract. Both pistons must be pushed back at the same time and rate with special tools. If unequal force is used, it is possible to scrape the pistons against the bores. This can damage the finish and coatings on the pistons and bores. Also, it can damage the seals.

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Andrew Markel

Andrew Markel is an ASE Certified Technician and former service writer, and he brings this practical knowledge to the Brake & Front End team as editor.
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