Q When I'm braking normally, the steering wheel on my 2006 Toyota Corolla with 31,000 miles starts to shudder. There is no vibration in the brake pedal, and there is no pulling to either side. The car stops normally. I notice it when the afternoon temps started to climb, but not in the cooler mornings. What could the problem be?

A There are several potential explanations. A sticking brake caliper slider or piston can cause the friction material to overheat, leading to inconsistent braking. Look for a bluish discoloration on the rotor surface. Worn, loose or damaged steering components such as a tie-rod end, rack or rack mounts can cause this shuddering as well.

And don't forget the tires. Your five-year-old tires with 31,000 miles on them may have developed an internal belt fracture or shift, or some type of strange wear pattern. Rotate the front tires to the rear to see if it affects the shudder.

Q I have a question about using the emergency brake. My friend told me to use it when parked facing uphill or downhill to protect the transmission, but I use it all the time. What is your advice?

A Because the front brakes provide most vehicles' braking power and parking brakes typically operate on the rear wheels, I tend to refer to this auxiliary system as the "parking" brake, not the "emergency" brake.

In an automatic transmission, the parking "pawl," or finger, mechanically engages into a notch to physically lock the transmission and prevent the vehicle from moving. When parked on an incline, it can be difficult to disengage when "leveraged" by the weight of the vehicle. So, when parking on a hill, hold the foot brake, shift into park, then apply the parking brake before releasing the foot brake. This prevents the weight of the vehicle from "leaning" on the parking pawl and makes it much easier to shift the transmission out of park when you're ready to drive again. And obviously, the parking brake provides a backup system to prevent the vehicle from moving while parked on an incline.

My advice on the use of the parking brake is this; either engage the parking brake every time you park the vehicle, or don't use it at all. Road salt, dust and dirt can cause the parking brake cables to stick if the system is not used regularly. And a stuck parking brake will make itself known by mechanical drag as you drive, followed shortly by a nasty bitter smell of overheated brake material.

Q My '99 Pontiac Bonneville's transmission shifts perfectly during first 10 minutes of driving. After warming up, it shifts with a slight pause and a mild thud sound but without any slippage. The dealership test-drove it after the 100,000-mile service and said it shifted normally. The transmission was serviced at 50,000 and 100,000 miles. Is transmission fluid viscosity a possible cause?

A Check for fault codes to see if the transmission has been operating in the "limp" mode, which is designed to protect the transmission from slipping. This could be caused by low hydraulic pressure, internal fluid leaks in the valve body, shift solenoids or accumulators, or even an engine problem such as low vacuum or a faulty throttle position sensor. Before spending big bucks on this issue, try adding half a can of Trans-Tune to the transmission fluid.