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Q AND A: 'Spongy' brake may have air in hydraulic system

QUESTION: I have a 2007 Honda Odyssey. When I'm stopped and push my brakes as hard as I c an, the pedal nearly touches the floor. It's a soft and spongy pedal, as if air is in the hydraulic system. The car stops adequately without having to depre...

QUESTION: I have a 2007 Honda Odyssey. When I'm stopped and push my brakes as hard as I c an, the pedal nearly touches the floor. It's a soft and spongy pedal, as if air is in the hydraulic system. The car stops adequately without having to depress the pedal really hard. Two dealers said the vehicle is operating properly.

ANSWER: I suspect air in the hydraulic system. My Alldata automotive database pulled up Honda service bulletin 07-045, dated March 2009, that addresses this symptom of a soft or low pedal. The likely cause is air leaking into the system from the ABS/traction control modulator control unit. The brake system should be bled manually to see if the pedal height returns to normal. If it does, the control unit should be replaced. If the vehicle is out of warranty, the bulletin indicates the repair may be eligible for "goodwill consideration."

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Q: The automatic transmission in my 2001 Buick Regal with 180,000 miles shifts normally in cold weather, but it shifts very hard when the weather is warm. I've changed the transmission fluid and filter every 40,000 miles.

A: Which is probably why the transmission is still operating at nearly 200,000 miles. Start by having a scan tool check for transmission fault codes. Problems such as binding, sticking or sediment in the pressure control valve or in the valve body can cause this symptom. It's also worth checking the connections in the 20-contact connector between the transmission and the powertrain control module (PCM).

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I would also suggest a test drive in warm weather with the scan tool still connected to see if the transmission fluid operating temperature is above normal, causing the transmission to operate in a "limp" mode. And finally, a half-can of SeaFoam Trans-Tune may help clean the pressure control valve and valve body.

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Q: I have a 2007 BMW X3. At about 10,000 miles it began having a very irritating, loud howl or whine in the rear end between 34 mph and 41 mph. The BMW service garage told me that this is normal on all BMWs and cannot be repaired, but the car is still safe to drive. Why should this howl happen at just 34 to 41 mph and then be quiet at all other speeds? Do you have any thoughts on what I can do or what is wrong?

A: Wear patterns on tires are often the cause of unusual howl, whine or drumming sounds, so start by rotating or replacing the tires. Next would be a careful check of the complete exhaust system and its mounts to see if some type of resonance is creating the noise. And check the rubber mounts for the rear final drive assembly.

Does the noise change or go away if you lift off the throttle at those speeds? If so, the noise may be from the ring and pinion gears in the rear differential.

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Q: A co-worker and I are having a disagreement about gas mileage. He maintains that if he is pulling a heavy load with his Suburban and uses 91 or 92 octane fuel instead of unleaded regular, he will get better mileage. I say it does not matter, and it's not good for the engine because of the carbon buildup on the pistons.

A: I agree with you. The rule of thumb is to use the lowest octane the engine will run properly on. Unless his vehicle is exhibiting symptoms of pre-ignition or detonation -- "pinging" or "knocking" sounds under load -- there's no performance, mileage or durability advantage to using higher-octane fuels.

Related Topics: TECHNOLOGY
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