Brackets

Fasteners for chassis anti-roll bars and torque rods provide the correct clamping force between anti-roll bar brackets, bearing supports, connecting rods and chassis or axle mounts. Depending on the vehicle configuration, these anti-roll bars and torque rods may be fitted to each axle. Bolts, lock nuts, washers and spacer sleeves must withstand fluctuating loads without loosening or deforming. Loss of preload causes fretting wear and knocking noises; eventually, mounting holes can become elongated or support brackets can crack. Simply fitting new anti-roll bar bushes will therefore not resolve a damaged bolted joint.

Always identify fasteners using the vehicle’s chassis number. Visual comparison or selection based solely on the model name is never sufficient. On MAN TGL, TGS and TGX or Mercedes Atego, Actros and Arocs, for example, specifications vary according to axle configuration, permissible axle load, anti-roll bar diameter and leaf or air suspension. On MAN Lion’s City, Mercedes Citaro and vans such as TGE and Sprinter, the specific suspension configuration also determines which fasteners fit.

In addition to the

 part number, check the thread diameter, thread pitch, bolt length, shank length, flange diameter and required strength class. Classes such as 8.8 and 10.9 are not freely interchangeable: bolts, nuts and bearing surfaces must be matched as a complete joint. In certain designs, the position of the unthreaded shank and its fit within metal sleeves are critical to load transfer.

Types include hexagon bolts, flange bolts, all-metal lock nuts, nylon-insert lock nuts and hardened washers. Only use the specified locking method. Material selection, such as quenched and tempered steel, and surface treatments such as zinc flake coatings affect corrosion resistance and friction. A different coating or unapproved lubrication can produce a different preload at the same tightening torque. Spacer sleeve lengths must also remain within factory tolerances to prevent unwanted compression of the rubber.

Typical symptoms include clicking when the suspension compresses on one side, knocking over transverse road joints and anti-roll bar mounts that repeatedly work loose. Rust marks around mating surfaces, bolt shanks polished by rubbing and displaced contact marks indicate movement where the joint should be clamped securely.

1. Secure the vehicle safely and support the chassis and axles according to the workshop procedure. Secure air-suspended vehicles against unexpected lowering. Relieve torsional stress in the anti-roll bar before removing fasteners.
2. Check brackets, bolt heads, threads and bearing surfaces for cracks, corrosion and deformation. Also inspect anti-roll bar bushes and connecting rods to identify the source of the noise.
3. Apply a controlled load to the joint using a pry bar. Measure relative movement between rigidly connected parts with a dial indicator; do not confuse elastic deformation of the rubber with play in the bolted joint.
4. Measure removed bolt shanks with a micrometer and mounting holes with an internal measuring tool in two directions. Compare diameters, ovality and sleeve dimensions with the manufacturer’s specifications. Check threads with a thread pitch gauge.

A torque wrench check alone does not prove that the correct residual preload is present: corrosion and static friction can mask a joint that is seized but provides insufficient clamping force.

Replace damaged fasteners and all bolts and lock nuts specified by the manufacturer as single-use. Do not repair elongated holes simply by fitting larger-diameter bolts; replace damaged mounts or follow an approved repair procedure. Clean mating surfaces and check that bolts do not bottom out in blind threaded holes before sufficient clamping force is achieved.

Assemble with the threads dry or lubricated as specified. Use a calibrated torque wrench and, where specified, angle tightening. Tighten joints that clamp rubber-to-metal bushes at the specified ride height. Afterwards, check for free movement and correct positioning, and listen for noises during a road test. Only carry out a follow-up check or retightening if specified by the manufacturer.