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BACKYARD MECHANIC: Noisy Tacoma truck could be easy fix

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QUESTION: We have a 2006 Toyota Tacoma Sport 4x4 with 100,000 km. We purchased it new. Of late, we have not been driving it as the problem that exists is annoying, if nothing else. When driving the vehicle, there is a sound like that of a whistle from a kettle that appears to be coming from the passenger side rear.

A technician, who worked for a Toyota dealership and now has his own business, took our vehicle for a ride and subsequently put it on his hoist, using a scope to identify what he believed was the problem. It was determined that the problem was the bearings in the differential.

New bearings were put in the vehicle and the owner/technician determined that the problem was fixed. Well, we took the vehicle to go shopping (round trip of 115 km) and, right from the start, the whistle sound was still there. We took it back and the shocked technician can't believe the problem still exists. He is at a loss as to explain what it could be. Any recommendations to solve our problem?

ANSWER: Toyota has a couple of bulletins out regarding differential noise on your year of Tacoma. The repair includes replacing the differential and installing sound-deadening materials beneath the carpet in the rear cab area. Because the bulletin requires they replace the complete differential instead of just bearings, I would assume the noise is caused by the gearset wear pattern, which in turn may have been caused by a bad bearing.

Diagnosing this type of problem can be difficult, because the noise may not be present or be different when there is no load on the drivetrain, such as operating the vehicle on a hoist. Driving down the road with the weight on the wheels and torque through the bearings and drivetrain components will typically cause the noise to be more pronounced.

Before you spend a lot of money on the rear axle, there are a couple other items to look at. Check that any dust shields on the differential pinion and driveshaft are not close to touching any other parts. Even if the parts are not touching but only close, it can create a whistling/howl type sound at speed.

Also, remove the driveshaft and inspect each u-joint for roughness or binding. A u-joint that has brinelled (washboard wear pattern usually caused by load or impact) can create a noise similar to what you describe. Hopefully the problem is in this area and will be easy to fix.

QUESTION: A technical question concerning turbochargers was answered in the November 2012 issue of Road and Track. One line in the reply to the writer's question caught me by surprise. (The question related to the Ford Focus Ecoboost engine but I assume it applies generally.)

The author stated the design life of a vehicle is 150,000 miles (250,000 km in our units.) This seems rather "unoptimistic" to me. I like to keep my vehicles for at least 10 years and the last was running great after about 350,000 km.

What does design life mean? Is this when major repairs can be expected to occur? If they are designed to last this long, why are warranties so low in comparison? How does this value for design life compare to vehicles manufactured a generation ago?

ANSWER: The design life of a vehicle component is an engineering estimate. In your example, the turbocharger was indicated to have a life of 250,000 km. This is under typical driving conditions with normal maintenance. I have heard them talk of a design life of 350,000 km for some of the diesel engine turbochargers.

These estimates of lifespan would indicate when a major repair may be needed to maintain the original performance level of the vehicle. Often, you can drive much further but performance may be decreased. In my experience, most vehicles will last far beyond the "design life." Hauling heavy loads, towing and performance driving will all shorten the life of components, so the design life is meant to include all common uses of the vehicle.

As for comparing this to vehicles built two or three decades ago, design life wasn't typically discussed back then, but looking at vehicle repair history and usage, new vehicles last much longer than before and require less-frequent repairs.

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.

kerr.jim@sasktel.net

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