Hard Core Light Truck

When Ford introduced the F-Series pickup, it did so with a poster that boasted its carrying capacity with a sky-high load of timber that would have made Paul Bunyon work up a sweat. Today’s F-150 is more likely to head to the forest for a weekend camp than a logging camp.

As with all light trucks and SUVs, today’s pickup is treated in much the same way as yesterday’s station wagon.

But they’re not station wagons, they’re trucks. Just beneath the surface, you’ll find a different assortment of parts, and a different set of potential problems.

Joe Cirino, who was the chassis product manager at Federal-Mogul for several years before recently moving over to handle the firm’s ACES catalogue data mapping responsibilities, says it is a market that continually keeps manufacturers on their toes.

“Parts in the industry, like a basic Chevy truck part, where the design has been around for 30 years will all of sudden start failing. Why is that?”

The short answer is that something must have changed. Sometimes vehicle manufacturers make changes to vehicles or vehicle packaging, but leave the underpinnings of the vehicle alone.

A good example is the increase in wheel and tire sizes on vehicles, and consequent changes to the suspension stresses.

“The tires and wheels are so much bigger and taller. The higher ride height puts much more load on the vehicle suspension, particularly the ball joints,” says Cirino.

Tom Byrnes, manager research and development for the company, elaborates.

“Take a look at your suspension. You have an upper and lower ball joint. Measure the distance from the ground to the lower, and up to the upper ball joint. The loads that are applied to those ball joints are a function of the distance between those ball joints and their distance from the ground. It is usually a two to one ratio.”

Byrnes says that the engineers refer to these points as L1, L2, and L3. If the wheel gets taller, for example, the ratio changes.

It can be thought of as a sort of lever, where the road seeks to lever the tire back and forth under cornering and bump forces.

The further from a ball joint the point of force is, whether that be the road surface or a bump, the greater the leverage it will have on suspension components, including wheel bearings, but especially items like ball joints that take a great deal of the force.

The whole situation is complicated by the fact that a single part can find itself in use in a number of vehicles.

“A single part can fit an extensive list of applications that go from passenger car to light truck,” says Ron Strain, program manager, chassis products, Affinia Canada. “From a manufacturer’s standpoint, you look at the worst case scenario.

“When you have done your engineering for fit, form and function, is there more to it? There is always a minimum specification. Those specifications may be the only things available to you.

“You look at the toughest applications, the most demanding applications, and that is what we are building to. We can incorporate those things that we have learned over the years so that when there is an opportunity to put those improvements in a part, that will make it last longer and perform better.”

Strain says that it is a constant learning process that allows companies with the R&D investments to use what they learn from today’s technology to improve parts that were intended for vehicles built in years past.

He says it is a case of continuous improvement, and backward evolution.

Some of those enhancements can have significant effects on the life expectancy of the part, such as the use of permanently attached boots or a case-hardened seat on a ball joint. Other times it can be a change that makes it easier for a technician to perform regular service, such as relocating a grease nipple.

In either case aftermarket suppliers must work within the existing design dimensions; an OE ball joint that was designed for “most drivers” but doesn’t stand up to the “worst case scenario” offered by Strain can’t just be replaced with an aftermarket part of larger size. Whatever the design enhancements envisioned by the aftermarket engineer, to some extent his hands are tied by decisions made at the OE level.

“We have to make our part fit the vehicle; but we can change our materials,” says Byrnes. And fit can be crucial. He says that parts of a design, such as taper, must be within 1/20th of a degree. Outside of that tolerance, he says, the part will fail prematurely.

And the work to understand OE designs and to improve on them continues.

Currently, the F-150 has employed a different type of stud on a variety of parts.

“It’s new to the industry and we’re trying to understand it. They use it on ball joints, tie rods and sway bars too.”

The design uses a stud with a shallow taper that takes a cone-shaped adapter, with a wider taper on the outside surface. Byrnes says they are still speculating about the reason for the change, but they have some good ideas.

“It is used on aluminum knuckles so when you increase that angle, it gives you more surface. If you took 65 ft.-lbs. and put it to 75 or 80-ft. lbs., that stud will pull through the knuckle. The wide taper spreads it out, so you can get up to 110-plus ft.-lbs. of torque.

“But we don’t know why they want to go that high.”

While the thinking at the OE level on that component may remain a bit of a mystery for now, there is little doubt that leading aftermarket companies will solve it by the time they begin to fail. And, if history is anything to judge by, they’ll improve it, too.

What kills bearings?

What is the most common cause of premature bearing failure? Being dropped prior to installation.

This causes fretting or brinnelling (a type of scoring) across the race the ball bearings roll in. Over time, the bearings will hit this score over and over again, causing premature wear.

A key additional cause includes water incursion, such as during off-road excursions or driving through deep water. This breaks down the grease inside the bearing and it is only a matter of time before the friction takes its toll on the bearing.

One example is a recent recall in the U.S. of the Kia Sedona. The rear-wheel-hub assembly on some minivans equipped with alloy wheels are prone to premature failure. What is causing this early failure is that the alloy wheels on some models allow water to accumulate around the dust cap on the wheel bearing; the standing water can infiltrate the bearing over time breaking down the lubricant. When that happens, the bearing begins to fail.

Bearings Going High Tech

Wheel bearings have been taking a beating on the highways and byways of Canada all winter and summer, with potholes and curbs vying for supremacy in the bearing wear championship.

Of course, along with many other areas of automotive technology, wheel bearings have not stood still.

“They are moving toward fully integrated hub assemblies as opposed to tapered sets,” says Tony Ramos, marketing, FAG Automotive in Canada. This, he says, echoes a similar move made in the passenger car segment over the past number of years.

He says that the units are becoming quite heavy-duty too, and that eight-stud units, looking like a scaled-down Class 8 truck hub, are also finding their way into the market.

He says that, at the OE level, virtually everything is going to hub assemblies. The notable exception is the super-heavy-duty class of vehicle that is still relying on the tapered bearing style.

One of the advantages for the OE is that a hub bearing will allow them to use the same unit for two- and four-wheel drive applications. “With the tapered sets, you would usually find a different set.”

What the integrated hub development means for the jobber, the service provider, and the consumer, is a greater cost.

“Now they come with the attachment to the wheel, the ABS sensor, sometimes traction control in one assembly. As these technologies come forth and get incorporated, the price is going up.”

The impact on inventory investment can be significant.

“The only way that a jobber could try to reduce that is they have to be smarter,” he says. He says that it means that each jobber is going to have to be more sophisticated in deciding what to stock, making hard choices to keep investments and turns in line with profitability.