Auto Service World
Feature   November 1, 2006   by Ron Henningsen

Changes in light trucks, SUV designs mean new challenges to the technician

Being both a truck and an automobile has placed additional stresses on chassis, brakes and ride control systems

Late model light-duty trucks (LDTs) and sports utility vehicles (SUVs) are complex machines. Three important systems on these vehicles are the chassis, the brakes and the ride control system. While seemingly simple, these systems are really are quite complex and present challenges to the technician.

In the old days, LDTs were known as half-ton trucks and all others — heavy-duty half tons, 3/4-ton and larger trucks were referred to as heavy duty. Back then SUVs — a name that hadn’t been invented — consisted mostly of International Harvester, some GM models designed as early Suburbans, some Dodge people haulers and Jeeps. Air conditioning was almost unheard of, and all of them rode like a truck. By today’s standards they were extremely crude. To repair these vehicles you didn’t really need a great deal of technical skill, except in the area of understanding wheel alignment angles.

Brakes on most of the early LDTs and SUVs were usually a four-wheel-drum; suspensions in the front were most often solid axles using king pins; and the rear end being a Hotchkiss set-up using leaf springs. If a technician today saw these vehicles on a regular basis they would think how crude and backwards they were. In the area of ride control on these early vehicles, the only variable was the installation of heavy-duty shocks. These were shocks that had a larger diameter piston, improved calving or sometimes an overload spring mounted on the outside.

In the late ’80s and ’90s the race was on to update existing models to supply the general public with affordable and attractive LDTs and SUVs. These LDTs and SUVs came in every shape and size, and with a wide range of design variations. These vehicles looked like they would do more from a load hauling, load pulling, handling, braking and ride standpoint. And people driving them often used them in a wide variety of driving conditions and environments because they seemed, and were often sold as being, a combination of a car and a truck.

Drivability puts new strains on the chassis

But such a combination has created several unique problems which today’s technician has to deal with. The most obvious is the trade-off between ride ability and load handling.

“Before, manufacturers of these vehicles took a standard truck chassis and then put an SUV body on top,” said Mark Christiaanse, director of product marketing with Tenneco Inc. in Monroe, Mich. “Today, the consumer expects the same comfort and ride ability as a passenger-type vehicle.”

This means the traditional chassis design has changed to provide that smoother, car-like ride that consumers expect now from LDTs and SUVs. But problems occur when those same consumers take the vehicles off-road, or expect them to haul or carry heavy loads like a standard truck or pickup, or operate in rough environments on uneven and messy terrain.

“As soon as you start loading those things, a tremendous strain is put on the upper ball joints,” said John Thody, owner and president of XRF (USA) Inc. in Marysville, Mich.

Thody added that strain over time can cause the ball joints on some LDTs and SUVs to fail, which is why his company has created a line of ball joint replacements that are made from high-carbon tempered steel for improved strength, have more degree of stud swing and come with rubber coverings.

“SUVs tend to get driven through mud puddles and pot holes with water, so all sorts of material, dirt and mud can get into the exposed joint,” Thody said. “So we thought it would be a good idea to put an accordion-type cover on the joint to protect the stud.”

In the area of wheel alignment on late model LDTs and SUVs, the trend by most manufacturers is to have an adjustable angle chassis/suspension, but to fix the manufacturing angles within a moveable range and then require an alignment kit to adjust the vehicle for a conventional service alignment. Many such vehicles exist today. The Ford Explorer, the Expedition starting in ’03 is another, the F-150 starting in ’04 and the Dodge LDTs starting in 2002 are all examples of this method of manufacturing.

To make maintenance of such systems easier for the technician, aftermarket parts manufacturers have come up with complete replacements kits for these suspension systems. For example, Tenneco’s Monroe Quick Strut unit is a complete, ready-to-install replacement strut assembly that includes all the components required for strut replacement in a single, fully-assembled unit. The Quick Strut features pre-assembled replacement bearing plate, upper and lower spring isolators, upper spring seat, coil spring, boot kit, and a Monroe Sensa-Trac strut.

The actual service, maintenance and repair procedures on late model LDTs and SUVs, in some cases, are very conventional while in other cases can leave a technician asking the question “why did they do that?” One chassis service example is when the upper control arm is an integral part of the upper ball joint as it is in the late model full-size Dodge, Explorer and several others. If the technician needs an upper ball joint they will often need an upper control arm as well. Removing and reinstalling the upper control arm will change the alignment so it’s recommended that the technician also install an alignment kit and realign the vehicle when the upper ball joint is replaced. As well, if the technician aligns one side of a vehicle they should align the other side.

Don’t forget the brakes

In the area of brakes there isn’t as much new on late-model LDTs and SUVs as there is in the area of chassis, suspension and alignment. This being said, any technician must realize that even though GM made a change back to rear drum brakes on many of its LDTs and SUV vehicles, four-wheel disc are here to stay.

Some vehicles are still using multi-piston calipers but within the area of true LDTs and standard SUVs, a floating single piston caliper is still the norm. Friction is continuing to be developed that gives a vehicle the pedal feel and stopping power, but dusting is almost an expected byproduct on some manufacturers. OE brake noise is no longer an issue for almost all LDTs and SUVs. Brake life is also excellent as long as the vehicle is used in a somewhat normal manner.

Dann Ingerbritson, technical instructor with the Affinia Under Vehicle Group in McHenry, Ill. added technicians should still pay particular attention to the braking systems of LDTs and SUVs because of the way they have been designed. The braking mechanisms are now made to improve the ride ability of the vehicles and to be light weight in order to improve fuel efficiency. However, these systems can wear rather quickly if an LDT or SUV is used more as a truck than a passenger vehicle. So it’s recommended that a technician examine the braking systems closely during regular maintenance and to ask the owner how the vehicle is being used to better understand the stresses the brake parts are experiencing.

“It used to be when you got a truck, you got truck brakes and you could haul anything you wanted,” he added. “That’s not the case now.”

Dirt, mud can really muck up ride control systems

Perhaps if there is one area on LDTs and SUVs that has lagged behind passenger cars, it is the area of ride control. Granted, there are some vehicles that have optional air spring suspensions on the rear, but for the most part it’s coil-on, conventional coil springs or torsion-bar front suspensions with standard hydraulic dampening and coil springs, leaf springs or air bags again with standard hydraulic dampening on the rear.

“A vehicle is a system. When a person puts several thousand dollars worth of tires and wheels on a vehicle they do little good if they don’t touch the ground,” said Carlos Falcigno, Program Group and North American training manager for Gabriel Ride Control Products Inc. in Brentwood, Tenn. “If you think about it, the ride-control system is what really makes and allows the chassis and brake system to work up to its design potential. Proper inspections are a necessity. Not enough time is spent on inspection service. If 40 per cent of vehicles need service only three per cent will get the recommended service.”

Carlos added that in the future vehicles with ride-control systems, chassis and suspension systems that fall outside the coil spring, leaf spring and torsion bar type will most likely have an aftermarket conversion to conventional coil springs. This conversion is now commonly done on passenger cars using air bag and air-ride strut systems along with some vehicles that fall just outside of the SUV category.

Affinia’s Ingerbritson added technician should also pay attention to is dirt getting into the electronic connections of ride control systems. Dirt can cause intermittent problems and sometimes those problems can be difficult to diagnose or to pick up during normal maintenance inspections. The technician should ask the vehicle owner about any kinds of intermittent problems and see if they can be reproduced, then examine the connection to see if dirt is the culprit.


Affinia Group

Gabriel Ride Control Products Inc.

Tenneco Inc.

XRF (USA) Inc.

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