Connecting rail

The telescopic steering shaft transmits steering torque from the steering column to the steering box or rack-and-pinion steering gear. Depending on the design, the sliding joint compensates for changes in length caused by cab movement, steering column adjustment or cab tilting. Torsional play causes delayed steering response; a seized sliding profile can transmit unwanted axial forces to the steering column and steering box. These two fault conditions must be assessed separately during diagnosis.

Telescopic steering shafts generally consist of steel inner and outer profiles combined with universal joints and clamp connections. Variants include splined sliding profiles, profiled sliding tubes, protective bellows and maintenance-free or regreasable needle bearings in the universal joints. Some sliding surfaces have a low-friction plastic coating. A telescopic joint is not necessarily a crash-energy-absorbing component; this function must be confirmed in the vehicle documentation.

Key design parameters include the compressed and extended lengths, usable sliding travel, minimum profile overlap, torsional stiffness, permissible angular twist and universal joint operating angles. The spline diameter, number of teeth, indexing and pinch bolt position must also match. Working pressure is not a selection parameter here: this component transmits steering torque mechanically.

Always identify parts using the vehicle's chassis number. A visual comparison or selection based solely on the model name is never sufficient. Also check the steering column design, steering box variant, left- or right-hand drive configuration and cab. MAN TGX models with XL, XLX or XXL cabs and Mercedes Actros models with Lang StreamSpace, Lang BigSpace or Lang GigaSpace cabs may have different connection geometries. Buses and vans, such as Citaro, Sprinter and TGE, have their own installation dimensions; truck versions are not necessarily interchangeable.

Typical symptoms include knocking when changing steering direction, noticeable free play, jerky steering and creaking during cab movement. Possible causes include worn sliding profiles, corroded needle bearings, damaged protective bellows or loose clamp connections. Stiffness after tilting the cab may indicate an incorrect installation position, insufficient remaining sliding travel or a distorted shaft.

1. Secure the vehicle safely with the wheels pointing straight ahead. Inspect the protective bellows, signs of corrosion, pinch bolts and contact marks. Secure a tilted cab with the specified mechanical safety device.
2. Ask a colleague to move the steering wheel back and forth through a small angle, following the manufacturer's procedure. Observe the upper joint, sliding joint and lower joint in turn to locate any lost motion.
3. Measure relative radial movement using a dial indicator on a stable mount. Determine torsional play using reference marks and an angle-measuring instrument under the specified test torque. Compare the results with vehicle-specific tolerances, not a generic limit.
4. After removal in accordance with the specified procedure, check each universal joint for smooth movement. If necessary, measure the sliding force over the permitted travel using a force gauge. Distinguish intended axial movement from unwanted radial or torsional play.

Replace components with cracks, deformation, binding universal joints or play beyond the manufacturer's tolerance. Welding, straightening or fixing sliding profiles in place at individual points is not a safe repair. Regreasing will not remedy worn splines; use only the specified lubricant where lubrication is permitted.

Before removal, secure the steering wheel against rotation to prevent damage to the airbag clock spring. Follow the safety procedure for the airbag system. Observe the correct indexing, joint phasing, insertion depth and tightening torques; renew fasteners where specified. After installation, check for free movement, sufficient remaining sliding travel and secure fastening. Finish with a steering function check and a road test; calibrate the steering angle sensor when required by the manufacturer.