Control arm

Straight torque rods in the suspension locate the axles relative to the chassis and absorb driving, braking and lateral forces, depending on their mounting position. Worn joints allow unwanted axle movement, resulting in directional instability, knocking noises and uneven tyre wear. These axle locating rods are not the same as steering rods or anti-roll bar links: their design and the direction of loading determine which replacement is technically suitable.

On MAN and Mercedes trucks, buses and vans, the axle locating arrangement varies according to axle configuration, permitted axle load and suspension type. Separate locating rods are particularly common on commercial vehicles with air suspension. Designs include straight longitudinal locating rods, transverse locating rods and triangular suspension links. They are not interchangeable. This category covers only the straight torque rods that locate the axles, not triangular suspension links. Depending on the design, rubber-to-metal joints or ball joints are used, with different torsional stiffnesses and permissible angular movements.

Always identify parts using the vehicle's chassis number. Visual comparison or selection by model name alone is never sufficient. On MAN TGS and TGX, Mercedes Actros and Arocs, or buses such as MAN Lion's City and Mercedes Citaro, for example, the axle code, suspension specification and mounting position are also decisive. For vans such as TGE and Sprinter, first establish whether the axle design in question uses a separate torque rod.

Check the centre-to-centre length, eye diameter, bush width, bolt diameter, angular orientation of the mountings and any adjustment capability. Depending on the design, rod bodies are made from forged steel or tubular steel sections with end fittings. In rubber-to-metal joints, the elastomer compound, bonding and radial stiffness also influence handling. Matching external dimensions alone therefore do not guarantee the correct load capacity.

Common faults include separation of rubber-to-metal bonds, torn bushes, corrosion around the mounting eyes and play in ball joints. Clunking during load changes or a rear axle that appears to steer under braking may indicate faulty torque rod joints. Incorrect ride height, worn chassis brackets or loose mounting bolts can cause similar symptoms.

1. Set up safely: chock the vehicle and support the chassis and axles in accordance with the workshop instructions. Never rely solely on the air springs. Check for play at the specified ride height and under the specified loading conditions.
2. Inspect visually: clean the joints and look for rubber debonding, displaced inner sleeves, damaged dust boots, rust traces around bolted joints and distorted rod bodies.
3. Measure play: apply a controlled load to the joint using a play detector or a suitable lever. Use a dial indicator to measure relative movement between the inner sleeve, outer housing and bracket. Distinguish elastic rubber deformation from free play; compare the results with the manufacturer's limits.
4. Check the geometry: measure the ride height at the specified reference points. Then check the axle position and thrust angle using axle alignment equipment. An incorrect thrust angle may explain the need for constant steering corrections and sawtooth tyre wear.

Replace bent, cracked or severely corroded torque rods as complete units; do not straighten or weld them. Individual joints may only be replaced where an approved repair procedure exists. In that case, check the bore for ovality and damage, observe the specified interference fit and use pressing tools that apply force to the correct metal component.

Inspect the adjoining brackets and bolt holes: a new torque rod will not remedy a worn mounting. Fit the specified new locking devices and bolts, and apply the correct tightening torque and any specified angle tightening. Fully tighten joints with bonded rubber bushes at the specified ride height to avoid permanent preload. Check the other locating rods on the same axle, verify the alignment and finish with a controlled road test. This prevents recurring symptoms from being wrongly attributed to the tyres or steering system.