Growing your strut service

Jan. 1, 2020
Struts affect steering, braking, stability, ride quality and road feel ? and they actually help keep the wheels firmly against the road so the tires can do their jobs, too. But unlike, say, brake pads that have wear indicators or sensors to indicate

Struts affect steering, braking, stability, ride quality and road feel – and they actually help keep the wheels firmly against the road so the tires can do their jobs, too.

But unlike, say, brake pads that have wear indicators or sensors to indicate that they’re worn out, struts often don’t cry out for attention when they need service. It’s usually up to technicians to notice problems in these important safety components during routine inspections, and that can happen only if the tech knows what to look for.

Most modern Asian-brand vehicles use MacPherson struts at all four wheels. These strut units are a space-saving system that combine the shock absorber, spring and often the bearing into a single unit. The units are often quite small and compact — making them a bit more difficult to inspect for crucial clues that service is required.

Even though it’s a bit more difficult to inspect these units, it’s well worth the effort since they’re so important to so many critical systems. And actually, inspecting and servicing MacPherson struts is easy (and profitable) once you understand what to look for and a few things to be careful of.

It may look intimidating, but it works just like a normal strut assembly. But using the right tools is critical.

Road Test
Ideally, the inspection process starts before the vehicle is even in the bay, with a good road test over various surfaces including both smooth and bumpy roads. One experienced technician I know follows the same set test route on every suspension-related road test, so he knows what to expect, knows he’ll be able to test everything and knows when something’s not right.

The test drive evaluates a few essential things.

First, the drive needs to determine if any strange noises are coming from suspension components (meaning they occur in relation to steering or suspension input, as opposed to engine or driveline input). Rattles and crunches often mean broken parts below.

The test drive should also check the vehicle’s reaction (body roll) during swerving and braking (dive). Excessive body movement usually means problems with the struts or dampers. Don’t go too crazy, but do move the vehicle around and make sure it’s pretty stable.

And the drive should also test for returnability of the steering wheel — in other words, that the steering wheel centers itself after a turn. If the wheels seem to bind or the vehicle has “memory steer” the problem may well lie in the strut assembly.

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Even if you didn't do anything to the alignment angles during strut service, this 2008 Highlander would still need an alignment. Note the tire wear on the inner edge.

One quick, obvious note: These tests should never be performed on major highways during busy times, bbecause these diagnostic maneuvers could cause an accident or mean explaining your actions to an observant police officer.

On-Ground Inspection
Once the vehicle is in the service bay, the next phase of the inspection begins.

Before shutting off and exiting the vehicle, turn the steering wheel from lock to lock to check for noises and binding, often indicating a problem with the bearing in the upper strut mount.

Then, in the bay, bounce test the vehicle by pushing one corner of the vehicle down and counting the number of bounces until it stops moving — a fairly good indicator of shock absorber performance. More than two or three bounces typically indicates problems.

Additionally, compare the height of the vehicle from one side to the other. This isn’t a scientific test or an official practice, but a huge difference from side to side does give you a hint that there might be a problem that needs investigating. It’s often difficult to find the repair manual’s height specifications. Some manufacturers have even moved away from measuring ride height, opting instead to specify other measurements such as Z-height (the distance between certain suspension components), so this quick field test often can save some time.

And as a final on-ground check, open the hood and have a look at the area where the strut mounts to the body. Look for signs of problems or movement with the mounting bolts — if they’ve been sliding around that usually indicates trouble. It’s also not a bad idea to take a look to see how high the strut comes off the wheel arch (Is it flush or does it stick up a bit?) to make sure the two sides are equal at this point as well.

Up in the air
Once the on-ground checks are done, the vehicle should go up in the air more a few more tests.

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It's normal on many Asian-brand vehicles to have a bit of a gap at the top mount.

One timesaving idea is raising the vehicle halfway up and then moving the wheel assembly from lock to lock by hand to check for any noises or binding, since the power assist system may have hidden something. Usually problems in the top strut bearing will show up during this step of the inspection. The wheels should move equally smoothly in both directions, and there shouldn’t be any grinding noises.

If there are problems, note them down and continue on with your inspection. There might be more problems to identify.

Leaks
Checking the strut assembly for leaks can be confusing since many struts have a light (completely acceptable) coating of oil around the cylinder.

This light coating of oil doesn’t mean that the strut needs replacing. Quite the opposite.

This light coating develops as the piston travels up and down in the cylinder, and the lubricant for the piston rod wipes itself off. (Oil running down the strut, however, does indeed mean that the unit must be replaced.)

Remember how the damper part of the strut works.

The damper is an oil-filled tube and piston assembly connected between the vehicle’s sprung weight (the frame and body at the upper part of the damper) and its unsprung weight (the wheels, and suspension at the lower part of the damper). As the coil spring moves, that piston is forced up and down in the damper tube.

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Ensure that salt and snow haven't collected in the base of the strut and rotted it out. Also, notice the bolts at the base of the assembly. They might be machined bolts to maintain or adjust the camber, with markings on teh head. Don't mix them up or the alignment will be off.

Dampers are one of the rare instances of a vehicle system where resistance is a good thing. The piston has tiny holes in it, allowing fluid to pass through it under very high pressure and only at a controlled rate. This slows down the piston, which this slows down spring movements. As the vehicle moves up and down along the road, that piston encounters resistance as it moves up and down though the oil filled damper tube — the resistance of the oil is what makes the damper dampen.

Because the damper tube is sealed, there’s resistance both downwards and also upwards during compression and extension. The compression cycle handles and dissipates the motion of the vehicle's unsprung weight, while extension handles and dissipates the vehicles heavier, sprung weight.

On Asian vehicles (as with most others), there’s more resistance during the extension cycle than during the compression cycle.

So, while the coil spring is what controls the height of the vehicle and absorbs the motion of the road and that vehicle, the damper (or shock or strut) at the center portion of the strut assembly is what dissipates that motion quickly and effectively.

Without the dampers in place, coil springs could just oscillate, uncontrolled, until the vibration dissipated on its own, which would take a while and also make for one heck of a stomach-churning ride in a car that would be very tough to control.

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Five ways to prevent noises from developing


Want to keep headaches to a minimum? Here are five things to watch for.

Make sure the spring is seated correctly, against the seats, top and bottom.
Torque the bolts correctly – unless there were damaged components, it should be the same height going back in that it was coming out.
Inspect the mounting bushings — if they’re too worn or ripped apart they’ll be noisy when the vehicle travels down the road.
Inspect the bearings — they need to move smoothly and quietly, and be free from rust and debris.
Ensure the top mounts secure where they bolt to the body, and that the clearances are OK (nothing will contact the hood and make noise).

Remember how the damper part of the strut works.

The damper is an oil-filled tube and piston assembly connected between the vehicle’s sprung weight (the frame and body at the upper part of the damper) and its unsprung weight (the wheels, and suspension at the lower part of the damper). As the coil spring moves, that piston is forced up and down in the damper tube.

The dampers used on modern Asian vehicles react automatically to road conditions — providing more resistance when the suspension moves up and down quickly, less resistance when moving slowly.

No matter how fast they’re travelling, dampers turn kinetic energy into heat energy, meaning they get hot! Keep that in mind when removing struts from a vehicle that just came off the highway.

One important note: The oil used in a strut or damper of an Asian vehicle is clear, almost amber colored liquid (I can’t think of a single exception!). So, if the fluid that’s running down the strut is a different color, it’s likely coming from somewhere else besides the strut and you’ll need to keep looking to find the problem — and also check and rubber components for swelling and damage.

Mounts
If you’ve been following these helpful hints, you’ve already checked the upper mounts for noise, binding and rigidity. Now it’s time to check out the lower mounts too (if equipped). Check that the unit is firmly mounted in place and that the bushings are intact (not separating or missing) on all four MacPherson strut units.

Springs
The springs on these systems are often very small any tightly coiled, so it’s tough to see cracks in the spring. But it needs to be done because they do crack and break.

One tip that may help is to look closely at the area where the paint is chipped or rust has developed. That’s often where the problem area is. Stones and debris often fly up and chip the painted surface on the springs, allowing water and salt to get into the spring, rust then develops, and the spring breaks. Broken paint doesn’t always indicate a broken spring, but it does indicate an area that needs to be inspected more closely.

Damage
Not sure why these vehicles seem so attracted to curbs, but for some reason they seem to get damaged quite often. If there are obvious signs of damage or bottoming out, take an extra look at the struts to make sure everything’s OK. Comparing the components on one side of the vehicle against the other may help identify a component that’s not as straight as it should be.

Replacing components
Removing the MacPherson struts from an Asian-brand vehicle is very similar to removing the struts from any other vehicle. Just mark the position of everything that will move, remove any brake hoses or wires attached to the strut, then undo the bottom clamps or bolt, undo the top mounting plate (NOT the center retaining nut yet — the spring is compressed and under a whole lot of pressure) and remove the unit.

When disassembling that unit, though, it’s important to keep everything in its original position. If you’re only replacing certain components on the unit — like a spring or strut bearing — there’s no shame in marking the components with tire chalk, or even white out from the office area, to make sure everything goes back where it was before. You could even take a digital picture if you’re really worried. Aligning everything correctly saves time (sometimes the strut will only fit one way) and prevents noises from developing after the repair, so it’s well worth the effort.

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Even though the units are small, the springs must still be safely compressed before the retaining nut is removed.

One important thing to consider is if the strut will fit safely into your spring compressor. The units used on these vehicles are often quite a bit smaller than you’d expect, and that can lead to problems compressing the spring. Even the bolt pattern on the top of the unit may not fit cleanly into the top portion of the spring compressor, causing a bit of a problem. Plan ahead, and be careful not to damage the threads on the top mount while compressing the unit.

And remember that these vehicles often use rather unusual bolts and fasteners. The thread pitch is sometimes very fine, and the bolts are unique to that purpose, meaning you can’t just grab another bolt out of the miscellaneous bolt tray if the fasteners gets lost or goes flying. Be careful to keep track of everything that comes off the unit.

Maintaining the Angles
Ideally, a vehicle should get a four-wheel alignment anytime work is done on suspension components, especially if anything affecting ride height was changed. But you can minimize the impact your work has on alignment angles.

The angles most likely to be accidentally changed during strut service are camber, the in-and-out tilt of the wheel at the top of the tire, and toe, the distance between the fronts of the tires compared to the rear of the tires.

If you’re the cautious type, have a look at the tires to see if the camber was causing problems before the vehicle arrived in your bay for strut work. If a tire’s are worn down on the inner or outer edge, there might have been a problem beforehand. Remember the difference between toe-wear and camber-wear? Toe wear is feathered or directional, while camber is smooth.

The most common way of keeping everything as lined up as possible it checking the dirt, pressure or wear marks on the other components, and reinstalling everything back where it was before. It’s not the most sophisticated method but it does work pretty well.

But if new struts are being installed on the vehicle, the matching marks method isn’t possible. In that case, note the possible adjustment points (if there are any — most commonly this means slotted alignment holes) and note how the old strut was positioned, trying to recreate the previous position.

But if all else fails and the vehicle is going for an alignment, try to keep the adjusters in the middle of their adjustment range to make the alignment process a bit easier.

Conclusion
Most Asian-brand vehicles use MacPherson struts, so there are plenty of them on the road.

Even though they can be a bit tricky to service and inspect, servicing the units’ vehicles isn’t tough. It’s actually quite rewarding.

Most of the problems come from lack of planning and rushing to get the job done, but that causes problems on all vehicles. With a bit of practice, you’ll be an expert at finding and fixing any problems that roll through your bay.

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