The Motorist's Pride
This comprehensive guide details the fundamental differences between drum and disc brake systems, covering their design characteristics, operational mechanics, and real world performance implications. Drum brakes function as enclosed systems where hydraulic pressure expands a wheel cylinder to push brake shoes outward against a rotating drum, creating friction through a self energizing action that can be prone to heat buildup and brake fade. Disc brakes operate as open systems where hydraulic pressure squeezes brake pistons to clamp pads against both sides of a spinning rotor, offering superior heat dissipation and consistent stopping power. Key advantages of drum brakes include lower manufacturing costs, effective parking brake integration, and longer lining life in some applications, while their disadvantages encompass poor heat dissipation, water sensitivity, and more complex maintenance requirements. Disc brakes excel with higher stopping power, better cooling, easier serviceability, and fade resistant performance, though they come with higher manufacturing costs and faster rotor wear. Typical usage patterns show drum brakes commonly on rear wheels of economy cars and older vehicles, while disc brakes dominate front wheels universally and are standard on performance vehicles and motorcycles. Practical insights highlight common issues like scored rotors, seized calipers, and brake dust buildup for disc systems, versus stuck adjusters, out of round drums, and pulling symptoms for drum systems. Technical notes emphasize the importance of regular cleaning and adjustment for drum longevity, and checking rotor minimum thickness during pad replacement for disc systems. The brake torque comparison reveals that disc brakes maintain higher clamping force during repeated stops due to better heat management, while drum brakes suffer from mechanical fade as heat causes drum expansion, increasing pedal travel.
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My 2011 Jaguar fault code P0105 tells me my MAP sensor is playing up, Have replaced sensor with genuine part, have since found out that my Barometric reading is at odds with my map sensor . The car ecm reads Baro pressure at ignition stage 1 then once started the MAP sensor takes over, (I think) The ECU Baro pressure reads 199kpa?? How can I change the Baro back to the 99kpa it should read. Many Thanks
Seeing a barometric pressure reading of 199 kPa on a 2011 Jaguar at ignition-on is a red flag, this value is physically impossible under normal atmospheric conditions.
At sea level, you’re looking at roughly 100 to 102 kPa, and even at the bottom of the Dead Sea (the lowest point on Earth), it doesn’t exceed 108 kPa. So, 199 kPa suggests either a serious sensor input error or a corruption in the ECU’s interpretation of the signal. On Jags of this era, the ECU performs a barometric pressure snap shot during key on before engine start, using the MAP sensor as the measuring device since there’s no separate BARO sensor. If the intake manifold or MAP port is contaminated, restricted, or sees abnormal pressure (like a stuck open EGR or boost control issue), it can skew this reading.
Yes, a faulty O2 sensor can cause this issue. It helps regulate the air-fuel mixture. If it's not working properly in cold conditions, the engine may run too rich or lean, resulting in rough idling and vibrations.
If it’s the O2 sensor, why would it only happen when the engine is cold? Wouldn’t it affect performance all the time?