Wheel bearing, not tire, is likely source of noise

Hey there, time traveller!
This article was published 17/03/2006 (7160 days ago), so information in it may no longer be current.

QUESTION — I would like to get your opinion on what could be the cause of tire noise. I have a set of Michelin Arctic Alpins on steel rims. The tire noise is most noticeable whenever I drive over pavement or any hard road surface and the sound increases when I go faster, but reaches a certain level and doesn’t get any higher. The sound is like a rolling hum. The tire pressure is correct, and when you look at the tires, they all look normal to me, lots of thread left, as they are only two winter seasons old. I have full wheel covers made out of plastic. This is the first season that this noise has started. I live in Winnipeg. Does the warmer temperature of this winter season have any effect?

ANSWER — Different type treads can make a significant difference in noise transmitted into the vehicle, but my experience with your tires has shown them to be relatively quiet on dry roads. Unusual wear patterns can also cause noise, but you say yours appear normal. Also, the noise has just developed, even though you have had the tires two years. Therefore, I suspect the noise isn’t coming from the tires. Instead, it is probably coming from a bearing.

You didn’t mention the type of vehicle you have. The noise is more likely from a wheel bearing although a final drive transmission bearing could also be the source if it is front wheel drive. If it is rear wheel drive, the pinion bearings or differential bearings could also cause noise.

Wheel bearings are best diagnosed by driving the vehicle and varying the load on each bearing. Steer from side to side at the vehicle speed where the noise is present. This places additional load on the side of the vehicle on the outside of the turn. If there is an increase in noise, then a wheel bearing is suspect. If the noise doesn’t change, then look at differential bearings. Noisy differential bearings will usually change as the vehicle is accelerated and decelerated.

QUESTION — As a first-time owner/hauler of a 5th wheel trailer, I would like your opinion on whether an extra transmission cooler is recommended for towing. The truck is a 2002 F150 XTR, 2-wheel drive, 4.6L engine, A/C, extended cab, shortbox. GVWR is 6050 lbs.

The trailer is a 1987 Prowler, 21.5 ft. 5th-wheel, tandem axle. Dry weight is 4100 lbs. Towing will be mostly flat prairie highway driving. Would it be wise to use a transmission fluid temperature gauge?

ANSWER — An auxiliary transmission cooler would be a good investment on any vehicle that is towing large trailers. Factory towing packages do include heavy-duty cooling systems for additional transmission and engine cooling, but transmission temperatures can skyrocket in seconds if heavy loads are placed on the vehicle. The cooler should be installed in the fluid line from the transmission to the radiator. This cools the oil before it goes into the radiator.

Your towing will be mostly flat prairie, but transmission temperatures quickly rise when you accelerate from a stop, climb any hill, or drive into a wind. Normal transmission temperatures will be in the 210 F to 230 F range but can climb over 300 F just pulling away from a stoplight. Heat is generated inside the transmission mostly by the torque converter operation. Oil starts to break down very fast at temperatures over 300 F.

To prevent this, accelerate with light throttle application. Operate the transmission in lower gears on hills or into the wind and don’t tow in overdrive. Use the mechanical advantage of the transmission gears. This allows the torque converter clutch to lock up more of the time, keeping temperatures lower. Your engine will be revving higher, but this shouldn’t be a problem.

A transmission temperature gauge isn’t necessary but it will increase your awareness of how you should drive. When the temperature starts to climb, back off the throttle or choose a lower gear. You may find yourself driving at 90 km/h instead of 100 sometimes because of wind or road conditions, but it will prolong the life of your transmission.

Jim Kerr is an experienced mechanic, instructor of automotive technology and member of the Automobile Journalists’ Association of Canada. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net