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FAQ Suspensions

WHY REPLACE RACK & PINION STEERING RATHER THAN REBUILD IT?

Overhauling a power rack is not a job for the novice. Special tools are required to remove and install internal seals. The tools are expensive and may not be cost justified for a shop that only does an occasional rack. For a do-it-yourself, the tools could end up costing as much as a new or remanufactured rack.

It is tricky to get seals properly positioned. If a seal slips or is damaged during installation, the rack will leak. For that reason alone, many professional mechanics won’t waste their time trying to rebuild questionable racks.

Operating pressures within a power rack generally do not exceed 100 psi when the wheels are in the traight-ahead position. In an easy turn, the pressure can increase to as much as 30,0 psi and it goes up to 700 psi in a tight turn. The highest pressures are usually
encountered when parking. If the wheels are up against a curb or if the steering wheel is turned hard against the stop, internal pressures can climb to 700 to 1,400 psi. This is why anybody who overhauls a rack better make sure the seals don’t leak.

Time is another important factor to the professional installers. Anything that makes their job easier and faster is money in theirpocket. If given a choice, most avoid doing repairs the old fashioned way because verhauling certain components in the shop slows them down and takes too much time. That’s why many components (like starters, alternators, front-wheel drive driveshaft assemblies, even brake calipers) are often replaced with new or remanufactured units rather than overhauled in the shop. The same is true for racks.

Time is money and at $40 per hour it doesn’t take long for a mechanic’s time to add up. By the time a mechanic spends $25 to $30 for a seal kit and several hours overhauling a rack (assuming it can be overhauled), he can end up spending as much of his customer’s money as if he had bought a replacement rack in the first place.

If the housing is worn, distorted, cracked or otherwise unusable, a new housing can cost upwards of $125. If the control valve is bad, it will cost $150 to $250 to replace -if you can find the parts. Individual component parts for racks are not readily available in the aftermarket because everyone knows it is cheaper and smarter to go with a new or remanufactured rack if the original rack needs to be overhauled.

Another reason why installers and do-it-yourselfers do not rebuild their own racks is because some racks are not rebuildable -at least not with a seal kit alone. If the teeth in the center of the rack are worn or damaged, a replacement rack bar can run $100 to $150.

Rebuilders can often salvage worn aluminum spool valve housings by boring out the housings and installing a stainless steel sleeve. The sleeve not only restores tolerances, but also prevents the wear problem from reoccurring. In that respect, a remanufactured rack may actually be better than the original. Most rebuilders also pressure test their racks after reassembly to make certain they function correctly and do not leak.

One mistake installers should avoid when replacing a rack is not flushing out the power steering pump and lines to remove all traces of old fluid. Flushing is a must because it removes contaminants that could ruin the replacement rack. The system also needs to be purged of air by cycling the steering slowly back and forth until there are no more air bubbles in the fluid.

WHY SHOULD SHOCKS AND STRUTS ALWAYS BE REPLACED IN PAIRS?

Unlike some steering and suspension components, there is no significant difference in wear rates between left and right shocks or struts. If one shock or strut is shot, chances are its companion also needs to be replaced.

For front versus rear, there can be differences in wear rates depending on vehicle loading and usage. Generally speaking, when front shocks or struts need replacing, so do those in the rear. Shock absorbers and struts are designed to dampen spring oscillations as the suspension goes through jounce and rebound. This prevents unwanted body gyrations and helps keep the wheels in contact with the road. The ride control elements inside perform this task by creating resistance, which in turn transforms the energy of motion into heat. The up and down strokes of the piston inside the shock or strut pumps fluid back and forth through metering orifices in the piston and valve
body.

After zillions of such cycles, the cylinder bore, piston and shaft seals eventually wear out. Though original equipment shocks have improved in recent years, many still may need replacing in as little as 30,000 miles. With struts, the lifespan is about double that of a shock.

The resistance created by these orifices helps dampen spring oscillations while limiting body and suspension motions. The pumping friction heats the fluid and the heat then dissipates through the shock body into the surrounding air. Problem is, most people do not notice the gradual deterioration in ride quality until things get really bad: Many shocks and struts are not replaced as often as they should be.

Replacement is needed if any of the following symptoms are noted:

-A bouncy or uncomfortable ride
-Nose dive when braking
-Excessive body sway when cornering
-Tail squat when accelerating
-Fluid leaks
-Physical damage to the shock or strut itself or its mounting hardware
-Cupped tire wear
-Indications of bottoming (check suspension stops)
-Vehicle fails a bounce test (more than two oscillations after rocking and releasing the
bumper)
-When the rod on a gas pressurized shock or strut does not extend by itself (indicating it has
lost its gas charge)

WHAT ARE THE SIGNIFICANT CAUSES OF EXCESSIVE TIRE WEAR?

Uneven or accelerated tire wear can be caused by wheel misalignment, worn suspension and steering components, and/or improper tire inflation. The most critical alignment angle with respect to tire wear is toe, Camber is also important and can be affected by caster. Misalignment is usually caused by worn, loose or bent suspension and steering parts (bad tie rod ends, idler arms, control arm bushings, ball joints, struts, etc.), but can also be due to spring sag or improper ride height.

With tire inflation, underinflation is just as bad as overinflation. Both can cause uneven tire wear. Underinflation can also make a tire run dangerously hot.

For a tire to roll down the road with the least amount of resistance and maximum directional stability, it must be aligned with the road, parallel to the other three wheels on the vehicle, square with the chassis, and properly inflated.

Rolling resistance is affected by a number of things, one of which is the straightness of the tire with respect to the direction of travel. If the tire is skewed slightly to one side or the other (toed in or out), it will scrub as it rolls. Scrub increases rolling resistance and also wears away the tread, leaving a feathered wear pattern.

Toe refers to the parallelism of a front or rear wheel to its companion on the opposite side. From a bird’s-eye view, all four wheels should be parallel to one another and pointing straight ahead.

Toe is measured by comparing the distance between the front edges of both tires on an axle to the distance between the trailing edges. If the distance between the front edge is further apart than that at the rear, wheels have toe-out. If front is closer together than rear, wheels have toe-in. Toe settings may be specified in inches, millimeters or degrees. Toe is most affected by worn tie rod ends, a worn or loose idle arm or center link, or a bent steering arm.

To minimize tire wear, rolling toe should be kept as near zero as possible. To achieve this, the compliance or amount of give in the vehicle’s steering linkage and suspension must be taken into consideration. As a vehicle starts to move, rolling resistance pushes the tires back.

With front-wheel drive, the situation is different because the front wheels pull the vehicle down the road. Engine torque causes the wheels to toe-in under load. Most FWD suspensions have a negative scrub radius built into the steering geometry.

The tire pivots slightly to the outside of its centerline. This helps to offset the tendency to toe-in. Even so, most front-wheel drive vehicles still require toe settings of zero to 1/8" toe out.

Toe also changes as the front wheels turn. Because the inner and outer wheels don’t follow the same path (the inner one follows a smaller circle than the outer one), the inner wheel must toe-out to compensate. This is called the" Ackerrnan Principle of Steering" after the engineer who invented the idea.

Toe-out depends on the angle of the steering arms with respect to the steering knuckles and chassis. The amount by which toe changes is called "toe-out on turns." This angle is also listed in alignment specs and is checked by turning the wheels on the alignment rack. If toeout on turns is off because of a bent steering arm, the tires will squeal and scrub whenever the wheels are steered.

Camber also affects tire wear. For directional stability, the tires must be perpendicular (straight up and down) with respect to the road. Any tilt to the inside or outside will cause a tire to turn in that direction like a bicycle leaning into a turn. This causes steering to pull to one side and creates uneven wear across the tread face.

Camber is the inward or outward tilt of the wheels as viewed from either front or rear of the car. If wheels lean in, they have negative camber. If they lean out, they have positive camber. The amount of camber is always expressed in degrees and is found by measuring the tilt of the wheels on an alignment rack or by using a level that attaches to the wheel.

Because camber affects tire wear, the ideal situation is to have zero running camber on all four wheels to maintain full tread contact with the road. Like toe, camber changes as the: suspension moves up and down. To keep the wheels vertical once the vehicle is loaded, a small amount of static positive camber may be required.

Camber should generally be within 1/2 degree side-to-side. Otherwise, the vehicle will lean toward the side with the most positive camber.

Camber misalignment can be caused by a sagging spring, a bent strut, bent spindle, worn control arm bushing, worn ball joint, or mislocated strut tower (too far in or out).

Camber corrections are made by replacing worn parts and/or by realigning the suspension using either the factory adjustments (cams, shims or elongated holes) or aftermarket aids.

Related items that may also need replacing include rack mounts and steering input shaft coupling. If the coupling donut is deteriorating with age, it needs to be replaced. Metal swivel couplings also need to be checked for rust and binding. Do not forget to include new power steering fluid (follow manufacturer recommendations as to the proper type of fluid).

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