Struts on A Car: A Comprehensive Guide
Thu Jan 01 1970
When you drive over a pothole, and your coffee stays in the cup, you have your suspension to thank. At the heart of that system—especially in modern vehicles—is the strut. While often grouped with "shocks," struts on a car are a distinct and vital component of your vehicle's anatomy.
What Are Struts?
A strut on a car is a major structural component of a vehicle's suspension system. Unlike a standard shock absorber, which is just a dampener, a strut is a structural link. It replaces the upper control arm and ball joint found in older suspension designs.
Think of the strut as the "leg" of the car. It connects the wheel assembly to the vehicle's body (chassis). Most commonly, you will find them on the front wheels of front-wheel-drive vehicles, though many cars use them on all four corners. The most popular design is the MacPherson Strut, named after the engineer Earl S. MacPherson, who invented it in the 1940s.
Uses and Function of Struts
Struts on a car are multitasking marvels. They don't just do one job; they handle three major tasks simultaneously:
- Shock Absorption: Like a shock absorber, the strut contains a hydraulic piston. As you hit a bump, this piston moves up and down against hydraulic fluid, converting the kinetic energy of the bump into heat. This stops the car from bouncing like a pogo stick.
- Structural Support: The strut supports the vehicle's weight. It holds the coil spring in place (which actually holds the car up) and keeps the tires aligned with the road.
- Steering Pivot: In front-suspension setups, the strut acts as the pivot point for the steering. When you turn the steering wheel, the entire strut assembly rotates, turning the wheels.
Benefits of Car Struts
Why do manufacturers love struts?
- Space Efficiency: Because the strut eliminates the need for an upper control arm, it frees up significant space in the engine bay. This is a huge advantage for modern front-wheel-drive cars that need to fit a transverse engine and transmission between the wheels.
- Simplicity: Fewer parts mean fewer things to break. A strut combines the spring, shock, and upper mount into one unit.
- Lower Weight: By integrating components, the suspension's overall weight is reduced, improving fuel economy and making the car feel lighter on its feet.
- Cost-Effective: For the manufacturer, it’s cheaper to build and install a single unit than to build and install a complex multi-link system.
Types of Struts
While the concept remains the same, struts come in a few different flavors depending on the vehicle's purpose:
- Standard MacPherson Strut: The industry standard. It features a shock absorber cartridge inside a structural housing, with a coil spring mounted around it.
- Coilover Struts: Short for "Coil Over Shock." While standard struts are technically coilovers, this term is usually reserved for performance aftermarket parts. These allow drivers to adjust the ride height (lowering the car) and the stiffness of the dampening for racing or sporty driving.
- Air Struts: Found on luxury vehicles (like Range Rovers or Mercedes). Instead of a metal coil spring, these use a rubber airbag pressurized by a compressor. This allows the car to raise or lower itself electronically and provides a "floating on clouds" ride quality.
- Sealed vs. Repairable Inserts: Modern struts are typically "sealed units"—when they wear out, you replace the whole thing. Older cars sometimes used "strut housings" where you could unscrew the top and just replace the internal shock cartridge (the insert) while keeping the metal housing.
All struts are shocks, but not all shocks are struts.
This is the most common point of confusion. To put it simply: All struts are shocks, but not all shocks are struts.
- The Shock Absorber: It is strictly a dampener. It does not support the weight of the car. If you removed the shocks from a truck, the truck would still stand at the same height (though it would bounce uncontrollably).
- The Strut: It is a structural partner. It supports the vehicle's weight. If you removed the struts, the vehicle would crash down onto its tires.
You will often see cars with struts in the front (for steering and space) and shocks in the rear (for durability and load management).
Buy All Types Of Struts
Symptoms of Bad Struts
Struts wear out gradually, so you might not notice the degradation day-to-day. However, once they fail, the signs are unmistakable:
- The "Nose Dive": When you hit the brakes firmly, the front of the car dips down dramatically. This increases stopping distance and is a major safety hazard.
- Rear "Squat": Conversely, when you accelerate, the rear of the car sinks excessively.
- Body Roll: The car feels unstable or leans heavily to one side when you take a corner.
- The "Cupped" Tire: This is a distinct wear pattern on your tires. Because the strut isn't keeping the tire firmly planted, it bounces slightly as it rolls, gouging out "cups" or scallops of rubber from the tread.
- Clunking Noises: A metal-on-metal clunk or knock when going over bumps usually indicates that the strut mount (the bearing plate at the top) or the internal valves have failed.
- Leaking Fluid: If you see oil coating the side of the strut housing, the internal seals have blown.
Replace Your Bad Strut With a New Strut
How to Inspect Your Struts
You don't need to be a mechanic to do a preliminary check.
- The Bounce Test: Park the car on flat ground. Walk to one corner of the car and push down hard on the fender/bumper, then let go.
- Good Strut: The car bounces up once, settles, and stops.
- Bad Strut: The car continues to bounce up and down 2 or 3 times like a boat on water.
- Visual Inspection: Turn your wheel all the way to the side so you can see behind the tire. Look at the metal cylinder of the strut. It should be dry and dusty. If it looks wet, oily, or has a thick layer of grime (oil attracts dirt), it is leaking and needs replacement.
- Road Test: Find an empty parking lot and drive slowly over a speed bump. Listen for clunks and feel for excessive sway.
How to Replace Struts
Note: This section focuses on the "Quick Strut" or "Loaded Assembly" method, which is the safest for DIYers.
Safety Warning: Struts are under immense pressure from the coil spring. Never remove the center nut on the top of the strut while it is still in the car. Doing so can cause the spring to explode outward with lethal force.
Tools Needed: Jack and jack stands, socket set (metric/SAE), breaker bar, torque wrench, penetrating oil (like WD-40).
The Process:
- Lift and Secure: Loosen the lug nuts, jack up the car, and place it securely on jack stands. Remove the wheel.
- Soak Bolts: Spray penetrating oil on the large bolts at the bottom of the strut (connected to the steering knuckle) and the nuts in the engine bay (strut tower).
- Disconnect Lower Mount: Remove the large bolts holding the bottom of the strut to the wheel hub/knuckle. You may need a hammer to tap these out.
- Disconnect Sway Bar Link: Most struts have a sway bar link attached to them. Unbolt this.
- Remove Top Mount: Open the hood. Remove the mounting nuts on top of the strut tower (usually 3 nuts). Do not remove the center nut.
- Remove Assembly: The entire strut assembly will now drop out.
- Install New Assembly: Slide the new "loaded" strut (which comes with a new spring and mount pre-assembled) into place.
- Tighten: Bolt the top mounts first to hold it, then reconnect the lower knuckle bolts and sway bar link. Torque everything to the manufacturer's specs.
- Alignment: Crucial Step. You must get a wheel alignment immediately after replacing struts, as the new parts will have shifted your wheel angles.
Strut Replacement Cost
Strut replacement costs vary significantly depending on whether you DIY or hire a pro, and what vehicle you drive. The following are estimates based on the Canadian market.
Price to replace struts:
- Strut Assembly (DIY): A single "Quick Strut" assembly typically costs between $150 and $400 CAD. Luxury cars or those with electronic suspension can cost upwards of $1,000 per strut.
- Strut Only (No Spring): If you only buy the bare strut (and reuse your old spring), the cost drops to $80–$150 CAD, but the labor is much higher/more dangerous.
Labor Cost:
- A mechanic will usually charge 2 to 3 hours of labor for a pair of struts. At Canadian shop rates ($100-$140/hr), expect to pay $200–$400 CAD in labor.
Total Job Estimates:
- Economy Car (e.g., Honda Civic): $600 – $900 CAD for a front pair.
- SUV/Truck (e.g., Ford F-150): $800 – $1,200 CAD for a front pair.
- Luxury Car (e.g., BMW 3 Series): $1,200 – $2,000+ CAD.
Order Your Strut at a Lower Cost
Recommendation: Always replace struts in pairs (both fronts or both rears). Replacing just one will cause uneven handling and braking.
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