Exceeding the permissible total backlash in the steering for a truck over 10 degrees is a direct basis for prohibiting the operation of the vehicle in accordance with the current technical regulations. For the driver and mechanic, this means that even with proper thrust tips, the force distribution mechanism itself requires immediate diagnosis or replacement. Ignoring this parameter leads to loss of course stability on the track and a critical increase in the braking distance when maneuvering in a limited space.
Owners of heavy commercial vehicles often confuse free running with the general wear of hinges, but the regulations clearly distinguish the permissible values for different classes of equipment. If the steering wheel does not start turning when it turns more than 10 degrees, the front axle wheels are considered to be malfunctioning. This requirement applies to all categories of trucks, regardless of the type of amplifier installed or the drive design.
Accurate diagnosis begins with mounting the vehicle on a flat hard surface and checking tire pressure, as soft rubber can mask the real problem. Mechanics use a special luftomere, but in the field, the use of a transporter or visual assessment by labels is permissible. It is important to understand that the total backlash consists of gaps in the driveshaft, the steering mechanism itself and the thrust hinges, so the search for the source of the beat requires the consecutive exclusion of each node.
Regulatory requirements and technical standards
The main document regulating the state of steering is GOST R 51709-2001which sets the free running limit values. For trucks with a gross mass of more than 3.5 tons, the maximum backlash angle should not exceed 10 degrees. Exceeding this indicator indicates a critical wear of the mated parts, which makes further movement dangerous for others.
Modern systems with hydraulic power (GURGor electrically amplified ()EUR) may have their own tolerances as prescribed in the manufacturer's manual. For example, for some models Volvo or Scania The allowable clearance may be even smaller due to the high sensitivity of the hydraulic system. However, in the framework of the state technical inspection, inspectors rely on the general rules of the road and GOST.
⚠️ Note: Operation of a truck with a back wheel of more than 10 degrees is prohibited by law and entails a fine, as well as a possible evacuation of the car to the parking lot.
Technical standards also take into account the design features of different generations of technology. Older models with a worm mechanism may have somewhat large gaps due to the design features, but even they must be within the legislative framework. New rack-type systems require more strict control, since the slightest wear of the gear pair immediately affects the accuracy of control.
History of regulatory changes
Previously, the USSR standards could differ depending on the type of car, but with the harmonization of standards with European requirements (UNECE), a single rigid limit of 10 degrees for all trucks was introduced, which increased overall road safety.
Methods of measuring free steering
Checking the total backlash should be carried out on a stationary car with a running engine, if the system is equipped with a hydraulic booster. This is necessary to create the operating pressure in the system, since with the engine shut down, the pump does not work, and the readings can be distorted by the resistance of the fluid. Measurement shall be made by swaying the steering wheel in both directions until the steering wheels begin to turn.
For accurate determination of the angle of rotation special devices-luftomers are used, which are attached to the steering wheel. In the absence of professional equipment, you can use a homemade pattern of cardboard with marked degrees or a ruler fixed fixed relative to the steering column. The technique involves fixing the initial position and subsequent measurement of the stroke before the wheels start moving.
It is important to take measurements in several steering positions: in the central position and with a slight shift to the left and right. This allows you to identify uneven wear of the gear or local damage to the shaft. If there is much more backlash in one sector than in another, this indicates the need to replace the entire steering mechanism.
The main reasons for the increase in backlash
The main cause of excessive free running is mechanical wear of friction pairs inside the steering gearbox. In the worm mechanisms, a pair of worm-sector is worn out, and in the racks - reiki teeth and gears. Over time, the gaps increase and the force transfer requires a greater rotation of the input shaft, which the driver feels as an "emptiness" on the steering wheel.
The second common problem is the wear of the steering rod joints and tips. Although technically backlash in thrusts is a separate parameter, it is summed up with the backlash of the gearbox during a general check. The broken fingers of ball supports or crumbs of the pendulum lever system also contribute to the overall picture of unstable control.
- 🔧 Development in the drive hinge of the steering shaft, which is often overlooked in diagnosis.
- 🔧 Weakening of the steering mechanism attachment to the frame or subframe, creating the illusion of an internal backlash.
- 🔧 Stifling of the hydraulic booster system or low fluid levels, leading to nonlinear work.
- 🔧 Deformation of the elements of the steering trapezoid after falling into deep holes or hitting the curb.
Corrosion and lack of lubrication in the nodes of friction accelerate the process of degradation of parts. In trucks operating in conditions of high dust or winter treatment of roads with reagents, the protective anthers (corrugated) are torn first. The entry of abrasive inside the mechanism leads to accelerated destruction of working surfaces and a sharp increase in backlash in a short period of time.
Impact of steering design
The design of the steering of the truck directly affects the nature of wear and adjustment methods. Worm-sector mechanisms have traditionally been used on heavy machines due to their high strength, but they require regular engagement adjustment. In such systems, backlash can often be compensated by a adjusting screw lift, but this is a temporary measure that hides real wear.
Rack mechanisms, more commonly found on light trucks and commercial vans, are considered less repairable in backlash conditions. If the rack is produced, adjustment is practically impossible without replacing the node. Modern systems with variable gear ratio have a complex geometry of teeth, and any backlash in them indicates a critical malfunction.
| Type of mechanism | Characteristic wear and tear | Adjustment | Resource before replacement |
|---|---|---|---|
| Worm-sector | Making a worm-roller pair | Possible (screw) | High-pitched |
| Ball nut. | Wear of balls and canals | Hard to do. | Very tall. |
| Rattle | Wear of reiki teeth | Not provided for. | Medium. |
| Screw (ERM) | Electric motor lux/shaft | Replacement of the node | High-pitched |
The presence of hydraulic power does not eliminate mechanical backlash, but only reduces the steering wheel effort. Moreover, malfunctions in the pair of spool-sleeve of the GUR distributor can create a feeling of “soft” backlash, when the steering wheel easily turns in the dead zone without liquid resistance. Diagnostics of such systems requires verification not only of mechanics, but also of the hydraulic part.
Adjusting the gap in the steering mechanism is a temporary solution that does not restore the resource of worn parts, but only masks the problem for a short time.
Consequences of operating with defective steering wheel
Ignoring increased backlash leads to a progressive deterioration in the handling of the car. At high speeds, the truck begins to scour the lane, requiring the driver to constantly correct the trajectory. This causes rapid fatigue and reduces concentration, which, combined with the large mass of the vehicle, creates an emergency situation.
In emergency situations, when a sharp maneuver is required to circumvent an obstacle, a large free move becomes fatal. While the wheels start to turn after the driver's command, precious fractions of a second and meters of braking distance will be lost. For a loaded truck, this often means being unable to avoid a collision.
- 🚛 Accelerated tire wear due to unstable wheel angle and vibrations.
- 🚛 Increased load on other elements of suspension and steering rods, leading to their breakdown.
- 🚛 The risk of a complete jamming of the steering at the most inopportune moment.
- 🚛 Legal liability of the driver in case of accident related to technical malfunction.
In addition, constant vibration and impact loads are transmitted to the steering column and the cab body. This can lead to cracks in the places of attachment of units and discomfort for the driver. Savings on timely repair of the steering mechanism turn out to be much more expensive for the restoration of adjacent nodes.
⚠️ Warning: Even if the car is turning normally, the presence of backlash above normal makes it technically faulty and dangerous for traffic on public roads.
Diagnostics and algorithm of fault search
To effectively eliminate the problem, it is necessary to localize the source of backlash. Begin the check with an external inspection of the steering rods and tips. The assistant must sway the steering wheel, and the mechanic must feel the connections for free running. If backlash is found in the tractors, their replacement will solve the problem, if not - the search continues at the gearbox.
The next step is to check the attachment of the steering mechanism itself to the frame. Weakened bolts can give a significant backlash, which is mistaken for wear of the insides. After that, the condition of the drive hinge of the steering shaft is assessed, which is often hidden under protective casings and requires removal for a detailed inspection.
☑️ Checklist of steering diagnostics
If all the external elements are serviceable, then the wear is inside the steering mechanism. In this case, the decision is made to repair or replace the unit. Repair is possible only with the availability of high-quality remixes and the qualification of the master, in other cases, the replacement of the unit is a more reliable and economically justified solution.
When replacing the steering tips, always check the condition of the pendulum lever and bushings, as their wear can negate the effectiveness of the new part.
Can the back of the steering mechanism be adjusted independently?
Adjustment of the gap in the steering gearbox is possible with a special adjusting screw, but this procedure requires accuracy. Excessive puff will lead to a biting mechanism and its rapid failure, and a weak one will not eliminate the backlash. It is recommended to perform this operation only if you have the experience and tools to control the effort.
Does the pressure in the tires affect the backlash readings?
Yes, low tire pressure can create the illusion of increased backlash due to deformation of the sidewall of the wheel at the beginning of the turn. Before checking the steering be sure to bring the pressure back to normal according to the specification of the car manufacturer.
What to do if the slug appears suddenly?
The sudden appearance of backlash most often indicates a breakdown: the tearing of the finger of the ball support, the destruction of the tip or the breakage of teeth in the gearbox. Operating a car with such a malfunction is strictly prohibited - evacuation and defective components are necessary.
How often should I check the steering on the truck?
Visual inspection should be carried out daily during pre-trip control. Detailed diagnostics with backlash measurement is recommended to be performed every 10-15 thousand kilometers of mileage or when the first signs of instability of control appear.