The safety of heavy commercial vehicles depends on the serviceability of the control system, where even minimal deviations can lead to catastrophic consequences. Drivers and mechanics often wonder what the wear threshold is and when it is still acceptable to operate without immediate repair. Understanding the physical processes that occur in the steering mechanism helps prevent accidents on the road.
According to the current technical regulations and traffic rules, relevant for 2026, there are clear restrictions on the amount of free steering wheel. For trucks with a gross weight exceeding 3.5 tons, this parameter is strictly regulated and should not exceed 10 degrees.. Exceeding this value automatically transfers the vehicle to the category of defective, prohibiting its further operation on public roads.
Ignoring this indicator creates a real threat not only for the driver, but also for other participants in the movement, since the handling of the car is sharply reduced. In the article we will discuss in detail the methods of measuring backlash, the reasons for its occurrence and legal aspects associated with the verification of this parameter during the technical inspection.
Regulatory requirements and legal aspects
The main document regulating the technical condition of vehicles is GOST R 51709-2001, which sets the limit values of free ride. For the category of trucks, as well as buses, the maximum permissible value of backlash is exactly 10 degrees. This value is the absolute maximum at which movement is still formally allowed, but experienced mechanics recommend starting the diagnosis already when it reaches 7-8 degrees.
Legally, driving a vehicle with a faulty steering system falls under part 2 of article 12.5 of the administrative code of the Russian Federation. This threatens the driver with a fine, and if critical malfunctions are detected during movement, the traffic police inspector has the full right to prohibit further operation of the vehicle until the defect is eliminated. Prohibition form The vehicle is issued on the spot, and the tow in this case may also be limited.
⚠️ Attention: An attempt to “cheat” the system by jamming the steering mechanism or temporarily tightening the nuts does not eliminate the cause of the backlash and can lead to a complete failure of control at high speed.
It is important to understand that the traffic rules of 2026 do not make exceptions for the age of the car or its mileage. Even an old truck must meet safety requirements. If during the check at a stationary traffic station or at a technical control point an excess of the angle of rotation is detected, the vehicle will not undergo diagnostics.
Physics of the process: what is free movement
Free travel, or backlash, is the angle of rotation of the steering wheel, at which the steered wheels of the car remain stationary. This is a gap between the gear teeth, the steering rod hinges and the fingers of the bicillary, which accumulates during operation. In an ideal mechanism, the rotation of the “drum” should be instantly transmitted to the wheels, but the wear of parts creates a dead zone.
Trucks are characterized by the use of power steering (HUR) and complex articulated traction systems, which increases the number of points of potential wear. Rack mechanisms and worm-prop have different designs, but the principle of backlash formation is the same: the appearance of gaps in the paired friction pairs. Wear in the steering rod hinges is especially critical, since it directly affects the accuracy of the trajectory.
A small backlash can even be useful to compensate for road irregularities, preventing the transmission of impacts to the steering wheel. However, when this parameter goes beyond the norm, the driver loses the sense of the road and is forced to make sharper and amplitude movements for maneuver. This increases fatigue and reaction time in an emergency.
Methods of measuring backlash on a truck
For accurate determination of the value of free ride in garage conditions or on the road, a special device is used - a luftomere. The most common type is a mechanical luftomere with a fixed arrow and a degree scale, which is attached to the steering wheel. The measurement process requires the fixedness of the steered wheels relative to the road surface.
The measurement procedure is carried out in the following sequence: the car is installed on a flat horizontal platform, the wheels are aligned in a straight line position. The engine must work so that the power booster is under pressure, simulating real driving conditions. The mechanic turns the steering wheel in one direction until the wheels start moving, then fixes the position of the arrow on the scale.
The steering wheel then turns in the opposite direction until the wheels start moving in the other direction. The total angle of rotation of the steering wheel between these two points is the desired backlash. If there is no specialized device at hand, you can use a conventional conveyor mounted on the steering wheel, although the accuracy of this method will be lower.
☑️ Luft measurement algorithm
There is also a method of assessment "by ear" and vibrations, but it is subjective and can not serve as a basis for official diagnosis. In the presence of a large backlash, a characteristic knock in the front suspension is often heard when the steering wheel is swaying from side to side on a standing car.
The main reasons for the increase in backlash
The main culprit of the free ride is most often the natural wear of steering parts. In trucks that operate in heavy conditions, the resource of the nodes is reduced due to constant vibration loads and shocks. The first usually fail ball supports of steering rods, in which liners or spherical surfaces are produced.
The second common cause is the wear of the worm-sector or gear-rail pair in the steering mechanism itself. Adjusting the engagement in these nodes allows you to compensate for wear, but only up to a certain limit. Excessive tightening of the adjusting screw can lead to a biting mechanism and loss of reversibility of the steering wheel, which is no less dangerous.
It is also worth paying attention to the following factors affecting the increase in backlash:
- 🔧 Weakening of attachment of the steering wheel on the shaft or the drive hinge of the steering column.
- 🔧 Wear bearings or bushings of the shaft of the binder, which creates an axial backlash of the entire mechanism.
- 🔧 Deformation or cracks in the steering rods and pads caused by impact loads.
- 🔧 Insufficient fluid level in the tank of GUR or suffocation of the system, which creates the illusion of increased backlash due to air compressibility.
⚠️ Attention: The use of non-original or cheap analogues of spare parts in the repair of steering can lead to a rapid reappearance of backlash and a decrease in the resource of the entire system.
Diagnostic table of malfunctions
To simplify the search for malfunction with increased backlash, it is recommended to use the following table, which links the symptoms with the probable causes and methods of elimination.
| Symptoms. | Probable cause | Elimination method |
|---|---|---|
| Knocking when turning wheels in place | Wear of ball rod supports | Replacement of tips or rods in the assembly |
| Heavy steering wheel + back lift | Low pressure in GUR, wear of the pump | Pressure check, belt or pump replacement |
| Steering at speed | Wheel imbalance, wear and tear of bushings | Balancing, replacing the bushings of the bicillary |
| Oil on the gearbox body | Wear of the shaft coils | Replacement of osteoils, checking of sapoon |
This table covers the most frequent scenarios, but individual defects are required in each case. Do not ignore the accompanying symptoms, such as leaks of fluid or foreign sounds.
Adjustment and repair of steering gear
If the diagnosis showed that the backlash is caused by a violation of the regulation of engagement in the steering gearbox, it is necessary to carry out appropriate work. To do this, the car is installed on the observation pit or lift. Before starting work, you should check the level of liquid in the tank of the GUR and the condition of the belt of the pump drive.
Adjustment of engagement is made by means of a special screw located on the body of the gearbox. Rotation of the screw requires caution: excessive clamping will lead to tight rotation of the steering wheel and rapid wear, and weak - will not eliminate the backlash. A critical parameter is the steering force, which should not exceed the values specified in the manual for the operation of a particular car (usually 0.3-0.5 kgf).
In cases where adjustment does not help, it is necessary to disassemble the mechanism and replace worn friction pairs. For modern trucks, replacement of the steering mechanism in the assembly is often offered, which saves time, but increases the cost of repair. When installing new parts, the front wheels must be descent-collapsed.
Prevention and maintenance of the system
To maximize the time of the emergence of critical backlash, it is necessary to comply with the maintenance regulations. Regular lubrication of hinges and drive hinges of steering shafts allows washing out abrasive particles and preventing corrosion. For off-road trucks, lubrication intervals should be reduced.
It is important to monitor the condition of the protective anthers on the steering rods and gearbox. Damage to the anther leads to dirt and water entering the mechanism, which causes accelerated wear of rubbing surfaces. Replacing a torn anther costs a penny compared to replacing an entire traction or gearbox.
It is also important to pay attention to the driving culture. Sharp steering on curbs, parking with emphasis on obstacles in a standing place (especially without GUR) and constant driving on broken roads at high speeds reduce the power of steering. Careful attitude to technology is the key to the absence of problems with backlash.
Frequently Asked Questions (FAQ)
Can I drive 11 degrees to the service?
This is prohibited by traffic rules and may result in a fine. However, if the service is several kilometers on a quiet road, you can drive, observing increased caution. On long distances and tracks with such backlash to go categorically impossible.
Does the pressure in the tires affect the amount of backlash?
The direct pressure in the tyres is not changed by the mechanical gap in the steering mechanism. However, low pressure can create the illusion of increased backlash or “wattiness” of the steering wheel due to deformation of the sidewall of the tire, which confuses the driver during the diagnosis.
How often should I check the backlash on commercial vehicles?
According to the rules of maintenance, the check of the steering condition must be carried out daily (before leaving the line) by the driver visually and by ear. Instrumental control of backlash is carried out with planned TO-1 or TO-2, as well as in case of suspicion of a malfunction.
Can I reduce the backlash by pulling the nut?
No, the nut lifting of the bicillary attachment only eliminates the backlash in the slither joint, if there is one there. If the backlash is caused by wear inside the gearbox or in the tips of the thrusts, the nut lift will not help and can lead to breakage of the shaft of the bicillary.