Trailing Arms with Fitting Position Front Axle, Rear Axle

A trailing arm runs forward from the axle or hub to a pivot on the chassis in a trailing arm suspension, holding the wheel against everything the throttle and brake pedal apply.

It is the component that stops the axle walking forward and back under load, and when the bushes in it perish the rear of the vehicle starts moving independently of the body.

What a Trailing Arm Does

The arm sits roughly parallel to the ground, pivoting at the chassis end and attached to the axle or hub at the other.

Its job is locating the axle fore and aft. Acceleration tries to push the axle backward, braking tries to push it forward, and the trailing arm resists both while still allowing the suspension to travel up and down freely.

On a solid rear axle it works alongside a panhard rod, which handles sideways location. Between them they hold the axle square and centred under the vehicle, with the trailing arms setting how far the housing can rotate and where it sits fore and aft.

Because the arm is rigid and the bushes are the only compliance in it, those bushes decide how much unwanted movement the axle is allowed.

An arm mounted behind the axle rather than in front of it does the same work and is called a leading arm.

Trailing Arm, Semi Trailing Arm and Twist Beam Layouts

Three arrangements use the name trailing arm suspension and they behave differently from one another.

A true trailing arm setup on a live axle typically uses two or three links plus a panhard rod. That is what most solid axle 4WDs run as their rear trailing arm arrangement, and it is the arrangement where the arms carry the heaviest loads.

A semi trailing arm is an independent trailing arm suspension, using a large roughly triangular arm pivoting at two points to locate each wheel on its own. Because the pivot axis is angled rather than square to the vehicle, camber and toe change as the suspension travels, which is a characteristic of the design rather than a fault.

A twist beam rear end joins two trailing arms with a crossbeam. That beam twists as the suspension works, so it acts as a sway bar as well as a structural member. Small front wheel drive cars use this arrangement almost universally because it packages well and leaves a flat floor.

Knowing which you have matters when ordering, since a twist beam is one assembly rather than two arms.

Why Trailing Arms Matter on a Lifted 4WD

On a solid axle vehicle, raising the ride height changes the angle the trailing arms sit at.

That rotates the axle housing, which on a rear axle affects pinion angle. Get that wrong and the universal joints in the tailshaft work at angles they were not designed for, which produces vibration at speed and shortens their life considerably.

Lifting also moves the axle slightly fore and aft, which shifts it within the wheel arches and can bring the tyres closer to the front or rear of the opening than intended.

Adjustable trailing arms exist for exactly this, allowing the axle to be moved back to where it should sit and the pinion angle to be corrected after a lift.

That correction tends to be overlooked, since the symptoms show up as a driveline vibration rather than as a suspension complaint and get diagnosed as a tailshaft problem.

What Causes Trailing Arms to Fail

Several things work on them, and the arm itself is rarely the first to go.

Trailing arm bushing wear is the most common cause by a wide margin. Rubber hardens with heat and age, ozone attacks it, and any oil or fluid contamination accelerates the process considerably.

Corrosion is the second, particularly on vehicles that see salt, mud or water crossings. It weakens the arm and it attacks the mounting brackets on the chassis, which matters as much as the arm does.

Impact is the third cause and the least predictable. Potholes and kerbs bend arms and crack bushes, and on an off road vehicle a hard landing does the same thing.

Overloading and towing beyond what the vehicle is rated for puts sustained stress through both the arms and their mounts.

The last cause is going unchecked for too long, since a small amount of play accelerates its own wear and a bush ignored becomes an arm and bracket repair.

Signs a Trailing Arm or Its Bushes Need Attention

• A clunk or thud from the rear when accelerating, braking or selecting reverse
• The rear of the vehicle feeling like it steers slightly of its own accord
• The vehicle not holding a straight line without correction at highway speed
• Uneven or accelerated rear tyre wear
• One side of the vehicle sitting visibly higher than the other
• A vibration through the driveline at speed on a lifted vehicle
• Visible cracking, splitting or separation in the bush material
• Elongated bolt holes at the arm's mounting points
• Cracking in the chassis bracket the arm bolts to
• The axle sitting further forward or rearward in one wheel arch than the other

The clunk when changing between drive and reverse is the classic one. It is the axle moving through the slack in a worn bush before the arm takes up the load.

Can You Drive With a Worn Trailing Arm

It depends on how far gone it is, and the answer sits between the two extremes people usually assume.

Early bush wear costs precision and tyre life without making the vehicle unsafe. You will hear a clunk and notice the rear feeling loose, and you can book the repair rather than stopping where you are.

Wear that has gone further than that is a different proposition. An axle with real movement available is changing its position under every acceleration and braking input, so the rear of the vehicle steers slightly on its own. That shows up worst under brakes in a corner, which is the moment it matters most.

A cracked arm or a cracked chassis bracket is a different category again. Those are structural, they fail progressively rather than gradually, and continuing to drive on one risks losing axle location entirely.

Towing with worn bushes is worth avoiding at any wear stage, since trailer forces load the arms considerably harder than normal driving.

How Long Trailing Arms Last

The arms themselves frequently last the life of the vehicle, with 100,000 kilometres being unremarkable and many going considerably further.

The bushes are the wear item and they reach the end of their life first, which is why most trailing arm work is bush work rather than arm replacement.

Australian conditions shorten the bush life rather than the arm life. Heat ages rubber, unsealed roads load the arms harder, and vehicles that tow or carry weight work them continuously.

The exception is corrosion, which attacks the arm and the bracket rather than the bush, and which can finish an arm well before its bushes are worn out.

Trailing Arm Bushes or the Whole Arm

Start with the bushes, since that is the cheaper repair and usually the correct one.

A rear trailing arm bush kit addresses perished rubber where the arm itself is sound, and on most vehicles that resolves the clunk, the wander and the tyre wear together.

Replace the arm instead when the bushing bore has worn out of round and will no longer hold a new bush, when the arm is bent or cracked, when corrosion has thinned it, or when you want adjustment the standard arm cannot provide.

Check the bore carefully once the old bush is out, because a wallowed bore is easy to miss on a heavy arm and a new bush fitted into one will not last.

Check the chassis bracket at the same time. Arms bolt into brackets that crack on older and hard worked vehicles, and a new arm in a cracked bracket solves nothing.

Upper and Lower Trailing Arms on Four Link Rear Ends

Worth separating, because a four link rear axle uses two arms per side rather than one.

The lower trailing arm sits below the axle centreline and takes the bulk of the fore and aft load under acceleration and braking. It is the longer and heavier of the two on most designs.

The upper trailing arm sits above it, shorter and angled, and its job is controlling how far the axle housing rotates rather than simply holding it in place. Because it is shorter, a given amount of bush wear at the upper arm produces more rotation at the axle than the same wear at the lower.

That difference matters when you are diagnosing a noise. A clunk under acceleration points more often at the lower arms, while a pinion angle that has drifted or a vehicle that squats heavily under power points at the uppers.

Both positions take the same abuse and both are worth checking together, since replacing lower arms and leaving tired uppers leaves half the rotation uncontrolled.

Trailing Arm Bushes Replacement Cost

Trailing arm bushes replacement cost is driven by access rather than by the price of the bushes, which are inexpensive parts.

Reaching them means releasing the arm at both ends, and pressing the old bush out and the new one in needs a press and correct tooling. On vehicles where the bush is bonded into a large arm, that pressing is the bulk of the time.

What moves the figure is how many bushes are being done, whether the fasteners come out cleanly, and whether the arm has to come off the vehicle completely or can be worked on in place.

Doing all of them at once is considerably cheaper than returning for the second pair, since the vehicle only goes up once and the alignment is only paid for once.

Replacing Trailing Arms and Checking Pinion Angle After

Support the vehicle and the axle before releasing either end, because the axle will move once an arm is free and it carries more weight than it looks.

Expect seized hardware at both ends on anything with age behind it. Penetrating fluid and time work better than force, and heat is often needed on the larger fasteners.

Work on one arm at a time where the design allows it, so the axle stays located by the other while you work.

Leave the pivot fasteners loose until the vehicle is back on its wheels carrying its own weight, then torque them. A bush takes a set from the position it is clamped in, and on an arm sitting under constant load, one clamped at the wrong height binds from the first kilometre.

Have the rear alignment checked afterwards on any vehicle with an independent rear end, and have the pinion angle checked on a lifted solid axle.

Fulcrum has been in suspension since 1976 and now runs 16 Service Centres alongside 200+ authorised workshops nationally. If you are unsure whether the fault is the bushes, the arm or the bracket, an inspection before ordering usually saves buying the wrong part.

Find Trailing Arms for Your Vehicle

Single arms are listed under individual trailing arms, and the wider suspension arms range covers control, radius and alignment arms.

Select your vehicle to see the trailing arms and bush kits available for it, in standard and adjustable specifications. Warranty and a fitment guarantee come with everything we sell, supported by workshops in every state.