Question: We have a 2009 Chrysler Town & Country with 63,000 miles on it. When we brake, it makes a relatively violent shake, and it's getting much worse, especially on the highway at speeds faster than 30 m.p.h. I have had the wheels checked and retightened with no luck. I don't see any enlargement of the lug holes.

Could this be wheel bearings, brakes, brake rotors, or what? The vibration starts in the steering wheel, but at upper speeds the entire van shakes.

Having a disability in our family, it's important we have a safe van. Should I take this to our dealer or a specialty brake shop?

We have a Chrysler extended warranty.

Answer: The most common cause for a heavy vibration when the brakes are applied is warped or worn brake rotors. Has the vehicle been in a crash or had a curb or pothole impact? Any bent or damaged wheel, tire, steering, or suspension component could contribute to this.

Steering rack mounts and worn inner tie rod ends are also possible causes. Worn MacPherson struts/shocks could allow minor vibrations to amplify dramatically.

I would suggest a complete brake, suspension, and steering component inspection as soon as possible. Since you have the extended warranty, the dealership might be your best choice, although brake components are considered normal wear items and would not be covered.

Q: I have a 2014 Honda Civic with a continuously variable transmission that feels sloppy. If I am rolling backward slowly (say, about 1 m.p.h.) and shift to drive, it takes at least two full seconds before engaging. This often startles me and feels dangerous.

I asked at the dealership and they said it was normal. What do you think?

A: I don't think you should shift into drive while rolling backward at any speed. Trying to engage drive while moving backward is never good for a transmission. It may not be catastrophic, but the engagement impact creates more mechanical stress.

In an automatic transmission, this action applies hydraulic pressure to a drive clutch that is rotating in the opposite direction, causing a somewhat sudden and violent engagement. In a continuously variable transmission, the belt/chain rotating in one direction attempts to engage the sheath/clutch that is rotating in the opposite direction, creating a similar sudden engagement.

I suspect the result of this type of engagement is normal, but the fact that it startles you and feels dangerous is a not-so-subtle reminder not to do it.

Q: I have a 2013 Toyota Tacoma pickup. It is a two-wheel-drive model with the four-cylinder motor and five-speed manual transmission. With a little more than 40,000 miles, the tires need replacing.

The original size tires are 215/70/15, and I would like to replace them with a set of 235/75/15 that I have on hand. I have done this on previous Tacomas I've owned with no problems.

Given today's more complex computer systems, can I swap tires without fear of damage to these systems?

A: As long as all four tires are the same size, yes. Since antilock braking, traction, and stability control systems monitor relative wheel speeds, this will not change if you install the larger tires.