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No More Free Tire ­Rotations!

Tire rotation is a cornerstone of vehicle preventive maintenance and tire longevity. It is a well-proven fact that tire tread life can be greatly enhanced by regular and timely tire rotation. During rotation, each tire and wheel is ­removed from...

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ASE G1: How To Measure Cold Cranking Amps, Reserve Capacity

The ASE G1 test contains 55 scored, job-related questions, 15% of which will concern electrical maintenance and repairs. From the ASE G1 study guide, you will need to know how to: • Perform battery tests (load and capacitance); ­determine needed...

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ASE A5: Brake Fluid And Bleeding Sequence

The ASE A5 Test includes a portion on brake fluid, bleeding, flushing and leak testing. You must know how to: • Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determine needed repairs. •...

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Modern Charging Systems: Cover All The Bases During the Diagnostic Process

To quote a familiar situation: “My customer’s car is now on its third alternator in six months and my jobber store refuses to ­warranty a fourth.” In other words, the parts supplier believes that an underlying problem is causing these alternators...

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Audi Fuel System: MIL On/Multiple Low Fuel Pressure DTCs

Due to fuel intrusion into the low-pressure ­system fuel pressure sensor (G410), a false signal may be sent to the controller, resulting in a reading that is out of tolerance. Model: 2007 Audi A4 Sedan V6-3.2L Scenario: The MIL is on and one or...

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Toyota: Check Engine Light Leads To New Battery Temperature Sensor

Complaint: The customer states the check engine light is on. Cause: A scan tool finds code P0517 – Battery Temperature Sensor Circuit High. A road test, while using the scan tool to ­monitor live data, finds the battery temperature sensor signal...

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Top 5 Tools: John Forro, AST, Automotive Service Technology in Hinckley, OH

John Forro AST, Automotive Service Technology Hinckley, OH ALLDATA Information System: I use this system daily for researching labor pricing, wiring schematics, circuit descriptions, torque specs, etc. One doesn’t need to memorize all the information...

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Phoenix Systems And NAPA Announce New Retail Agreement

Phoenix Systems has announced an agreement with NAPA/Balkamp to put Phoenix Systems products in their stores. As part of this agreement, NAPA locations will now have access to BrakeStrip Brake Fluid Test Strips and the New NAPA Service Tool 2104-B Reverse...

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MAHLE Service Solutions Unveils New Website

MAHLE Aftermarket, Service Solutions, formerly MAHLE RTI, has introduced its new website at www.servicesolutions.mahle.com. The site contains updated information on MAHLE Aftermarket’s newest division, providing visitors with a clean, user-friendly...

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Must-Read TPMS Technical Service Bulletins

Here’s a rundown of the top technical service bulletins related to TPMS. These TSBs should be analyzed by every technician that services TPMS. Audi TSB Number: 4413382034445/1 Models: 2010-’14 A4/S4, A5/S5 and Q5 Summary: This TSB addresses TPMS...

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Ford Reflash: Setting Up Your PC

You’ve just finished up a job on a Ford vehicle, and you’re about to try and start it up. However, it needs programmed first. You’ve decided to use a J2534 tool, but there are certain things you’ll need to consider ­before purchasing that subscription...

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Fuel Line Replacement: The Why and How

If you live in a state that doesn’t get snow, you can stop reading right now. If you live in the Snow Belt, you are about a month away from snow and ice. It’s not the adverse driving conditions that should scare you or your customers, it’s...

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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.

Latest posts by Andrew Markel (see all)

  • anthony daurnhime

    yeah 2 is always better then 1

    • Danny

      Sure thing

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