Hydraulic Suspension Bushings

[Counterman]

If a customer mentions that they’re seeing fluid trickling from a suspension bushing, their eyes aren’t playing tricks on them. That bushing could be hydraulic.

Hydraulic suspension bushings were developed in response to customer demands for smoother, quieter and better-handling vehicles. To achieve this, sophisticated suspension components are needed. Modern suspension systems look a lot different than they used to, with multiple links used to maintain suspension geometry.

A non-hydraulic suspension bushing typically will feature a number of empty voids inside them. These voids are a product of clever engineering, and they allow for deflection/compression in a specific direction when placed under load. Hydraulic bushings fill those empty voids with a fluid. This fluid works like a hydraulic damper, while still allowing for deflection/compression when under load.

The word “hydraulic” might imply that hydraulic fluid or oil is used inside these bushings, but they typically use a glycol mixture instead. Oil or hydraulic fluid would break down the rubber inside the bushing and cause it to fail prematurely. If you’ve ever seen a radiator hose that got coated in engine oil, you know what we’re talking about.

These bushings are engineered with a certain tire and wheel combination in mind. This means increasing the tire and/or wheel sizes can throw this off, and the suspension may need to be repaired more frequently.

Hydraulic bushings are able to isolate noise, vibration and harshness (NVH) from entering the vehicle cabin more effectively than standard bushings. Hydraulic bushings can be firmer without compromising passenger comfort, leading to crisp steering response and road feel. They will deflect less under load, such as braking or hard cornering, and this means better vehicle stability.

But, all bushings eventually will wear out and need to be replaced. Hydraulic bushings may crack, rip or tear, just the same as non-hydraulic bushings will. The big giveaway is the hydraulic fluid leaking from the bushing.

Failing hydraulic bushings typically exhibit one or more of the following symptoms:

• Clunking or knocking noises while braking or turning
• Evidence of fluid leaks coming from the bushings
• Unwanted suspension movement
• Tire wear (from excessive suspension movement)
• Increased NVH transferring into the vehicle cabin

Replacement Tips

Hydraulic bushings likely will be more expensive to replace than standard bushings. Here are a few tips and tricks to share with your customers.

Let’s start with the most important tip: Always check the OE service information. Even if your customer has performed this type of repair in the past, it’s still a good idea to check the service information to see if anything has been updated recently. They should road-test the vehicle before and after the repair.

If your customer is pressing a hydraulic bushing into or out of a suspension arm, they should be careful not to apply force directly against the rubber part of the bushing. Doing this will most likely rupture the rubber bushing, causing the hydraulic fluid to spill all over the floor. Once this happens, the bushing is ruined and must be replaced. Be sure to only apply force against the outer race or sleeve.

Modern bushings likely will feature some sort of locating mark, notch or indicator. Reference the OE service information to learn how to correctly align the bushing to the suspension arm. Doing this will allow the suspension to articulate properly. Failure to do this may cause the suspension to bind up during movement, and/or cause the bushing to wear out or fail prematurely.

It’s strongly recommended to wait to torque the fasteners down to specification until the suspension has been set to normal ride height. If the fasteners are tightened down with the vehicle in the air, the bushing will be forced to twist when the vehicle is lowered onto the ground. This means that the bushing will always be twisting at normal ride height, and this will surely lead to premature wear, tearing and/or failure.

Finally, your customer should perform a four-wheel alignment if the service information calls for it. Some suspension components may not require an alignment after service; it depends on the make, model and application.

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