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Q: I have a suggestion, not a question. I have evergreen trees hanging over my driveway and the tree sap on the vehicle is hard to remove. I tried a variety of products and had little success. But what seems to work is Off insect repellent in the orange spray can. Spray it on, wait a few seconds and wipe it off. Then clean with soap and water. It doesn't seem to harm the paint.

R.R., Mundelein, Ill.

A: Maybe the SC Johnson company should begin marketing it as Sap-Off. We are going to file this tip along with the ones suggesting toothpaste to clean discolored headlight lenses.

Q: Let's say I need to slam on the brakes but the pedal won't work, so I quick pull back hard on the hand brake. What happens? Which wheels brake? Do the wheels lock and the car skids? Will the car be brought to a rapid, safe stop?

R.H., Hinsdale, Ill.

A: The rear wheels will lock up and the car will go into a spin. It is known as a bootleg turn or handbrake turn and competition drivers use it to their advantage, knowing precisely when to release the hand brake and accelerate. It is a quick way to make a 180-degree turn in a small area. Do not try this at home!

Q: I have a 2010 Mazda3 hatch with an "auto-manual" transaxle. Normally I use "D" and let the car select its own gear settings. Once in a while when approaching a suburban stoplight at 30-35 mph, I switch to "M" (manual) and flick the lever to physically downshift to third then to second gear and have the engine slow the car for four or five seconds before using the brakes. The owner's book says that the system will prevent me from taking this action if the engine or vehicle speed is too high to be done safely. What's the trade-off on engine wear and fuel economy vs. brake pad life (or any other considerations) between the two methods?

B.M., Palatine, Ill.

A: This is a feature becoming more common on many cars and some even have paddle shifters on the steering wheel to make shifting more convenient. Similar systems are the norm for Formula 1 racing, making shifts much faster than a human can with leg and arm. But race cars have manual gearboxes plus a single- or dual-disc clutch. Your car has a fully automatic transmission and all you are doing is activating the shift solenoids instead of allowing the computer to do so. You won't hurt or help anything and, as you noted, the computer will not allow the shift if the engine speed is not correct. So, go ahead and have fun.

Q: I recently had to replace an A/C blower in my 2015 Subaru Outback. The dealership said my cabin filter needed to be replaced. I replaced it; it was a charcoal cabin filter, which may have appeared dirty to the technician. Is it worth the extra money to buy a cabin filter with charcoal?

R.S., Glen Ellyn, Ill.

A: We prefer the activated charcoal filters. Not only do they filter particulates such as dust and pollen, but they trap many exhaust fumes and other objectionable outside odors.

Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber's work appears in professional trade magazines and other consumer publications. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to