A sharp hum or metal grinding in the area of the rear wheels when dialing speed often signals critical wear of the main gear or differential bearings. Bridge in the truck It is one of the most loaded transmission units, and ignoring the first signs of malfunction can lead to jamming of the wheel pair and expensive downtime of equipment. Unlike passenger cars, here the loads are calculated in tons, and the failure of the node on the track creates an emergency situation.
Diagnosis should begin with checking the level and condition of the oil, since it is the lubricant that removes heat from rubbing vapors. Carter Bridge It works in an aggressive environment where the combination of high temperatures and shock loads requires constant monitoring of the sealing of the osteoils. If you notice oil stains on the inside of the wheel discs, this is the first sign that the seals require immediate replacement to avoid dry friction.
Modern freighters bridge-bridge equipped with complex differential locking systems and interaxial gearboxes, which complicates the process of finding a fault. The owner or mechanic should clearly distinguish between the noise of the hub bearings and the hum of the main gear, since the methods of their elimination are radically different. Below we will discuss in detail the design, typical breakdowns and routine work to maintain the unit in working condition.
Design features and types of bridges
The main function of any bridge is to transfer torque from the engine to the wheels and to perceive vertical loads from the mass of the car. In freight transport the most common cutting-outwhere the crankcase is divided horizontally, which facilitates access to the main gear. Structurally, the unit consists of a beam, stockings, main gear gear gearbox, differential and hub nodes.
There are two main types of design: with and without wheel gearboxes. In the first case, the torque is transmitted through the semi-axles to the planetary mechanisms located directly at the wheels. Wheel gearboxes allow to increase ground clearance and reduce the load on the semi-axles, which is critical for dump trucks and off-road equipment.
- 🚛 Central gear: It changes the direction of rotation by 90 degrees and increases torque.
- ⚙️ Differential: Allows the wheels of one axle to rotate at different speeds when cornering.
- 🛑 Lockdown: Forced to connect semi-axes to increase patency in dirt or on ice.
⚠️ Attention: Operation of a truck with the differential lock on a hard surface with good traction is strictly prohibited. This leads to breakage of semi-axles and cutting of gear teeth due to the lack of wheel slip when turning.
Railless bridges, often referred to as "single-stage" bridges, are lighter in weight and easier to maintain, but require a stronger beam. The choice of type depends on the purpose of the car: for main tractors, economics and speed are important, and for construction equipment - permeability and reliability under load.
Technical nuances of planetary gearboxes
Planetary transmissions use a circuit where the sun, satellites and the crown gear work in an oil bath. The feature of such nodes is a high sensitivity to the purity of the oil. Even microscopic metal shavings can jam satellites, causing the destruction of the entire mechanism.
Typical malfunctions and their symptoms
To determine the nature of the breakdown is often possible by sound accompaniment of movement. Bridge buzzing, which increases during acceleration and subsides when the gas is discharged, usually indicates wear of the teeth of the gears of the main pair or improper adjustment of the contact spot. If the noise changes when you turn, the problem is most likely to be the differential bearings.
Vibration of the driveshaft transmitted to the bridge may indicate an imbalance or wear of the crosses, but sometimes the cause is the beating of the flange. gear-carrying. It is important to conduct diagnostics consistently, excluding drive transmission before removal and defection of the gearbox itself. Knocking at a sharp start or braking the engine indicates the presence of backlashes in slit joints or wear of satellites.
| Symptoms. | Probable cause | Elimination method |
|---|---|---|
| Spread-out hum | Wear of the main pair | Replace gears, adjust the spot |
| Knocking on corners | Satellite wear and tear | Defective differential |
| Heating the crankcase | Lack of oil or a tight bearing | Level check, bearing replacement |
| Oil leak | Wear of ossels or gaskets | Replacement of seals |
Overheating of the node is a separate and dangerous category of malfunctions. After a long trip, bridge-case It is impossible to hold with your hand, so the heat exchange is disturbed or the lubricant has lost its properties. This can be caused by the use of oil of inadequate viscosity or excessive tightening of bearings.
Regular maintenance and oil replacement
Timely replacement of transmission oil is a key factor in the durability of the unit. In the process of work, metal shavings, wear products of friction disks and moisture accumulate in the oil. Class oils are used for cargo bridges API GL-5 with anti-scoring additives that withstand extreme pressures.
☑️ Checklist for bridge maintenance
The frequency of replacement depends on the operating conditions. In severe conditions (construction, off-road, frequent overloads), intervals should be reduced by 30-40%. Before pouring a new composition, the condition is necessarily checked sapoon. Clogged sapoon creates excessive pressure inside the crankcase, squeezing oil through the glands even with serviceable seals.
The replacement process does not require complex equipment, but requires cleanliness. Getting dirt or water inside the gearbox is equivalent to abrasive action, which will quickly put the grinded surfaces of the gears out of order. After replacement, you need to drive several kilometers and re-check the level, as the oil should disperse to all cavities.
Expert advice: When changing oil, always pay attention to the color of the magnetic chips on the cork. Gray plaque is the norm, large metal flakes or "fluff" indicate the beginning of the destruction of bearings or gears.
Adjustment of main gear and bearings
Assembly and adjustment main-transmission This is a high-precision operation that requires the use of dynamometer keys and indicator racks. The main parameter is the contact spot of the gear teeth, which is checked by applying a special paint. The shift of the spot indicates the need to select adjusting washers.
The pre-tension bearings of the leading gear and differential also play a critical role. Insufficient tension leads to the appearance of backlashes and knocks, and excessive - to rapid overheating and destruction of clips. For each model of the tractor there are factory tolerances, deviation from which is unacceptable.
- 🔧 Selection of washers: ensures the correct position of the gear relative to the driven wheel.
- 📏 Measurement of gap: It is carried out by a probe between the gear teeth at several points.
- 🔄 Moment of the turn: is checked by a dynamometer on the flange of the leading gear.
To perform these works "by eye" is absolutely impossible. Incorrect adjustment will cause the new set of gears to fail after several thousand kilometers, emitting a strong howl. Quality adjustment ensures quiet operation and uniform distribution of the load on the surface of the tooth.
⚠️ Attention: It is forbidden to use sealants that are not resistant to the aggressive effects of transmission oils. Conventional silicone can dissolve, clog oil channels and lead to oil starvation of bearings.
Diagnosis of hub nodes and semi-axes
The hub of the truck carries the entire mass of the car and cargo, so the condition of its bearings requires constant monitoring. The luft of the wheel, felt when the car is swaying with a jack, indicates the need for adjustment or replacement tapered bearings. Ignoring backlash will lead to crashing seats and expensive repairs.
The bands transmit a tremendous torque and are subject to twisting loads. Visual inspection for cracks, especially in the area of slits and flanges, is mandatory at each removal of the wheel. Fatigue cracks can develop imperceptibly and lead to breakage of the semi-axis in motion, which is fraught with loss of control.
Hub oels are consumables, but their replacement is often delayed until leaks appear. Modern cuffs are made of materials that are resistant to high temperatures, but they are afraid of mechanical damage during installation. Installation of a new ossil should be made using a mandrel so as not to damage the working edge.
Critical moment: Luft in the hub of a truck is unacceptable. Even the minimum beating of the wheel destroys the bearing in a few hundred kilometers.
Frequent errors in repair and operation
One of the most common mistakes is mixing oils from different manufacturers and viscosity classes. Chemical reactions between additives can lead to precipitation, which will clog the thin channels of lubrication and disable lock-up. Always drain the old oil completely before pouring the new one.
The use of non-original parts of poor quality is the second reason for early failures. Cheap bearings are often made of soft steel that does not undergo the necessary heat treatment. As a result, they quickly lose geometry, causing shafts to be distorted and the destruction of other transmission elements.
Some drivers ignore the heating up of the transmission in winter, starting with high speeds. Cold, thickened oil cannot effectively lubricate rubbing vapors, which leads to oil fasting in the first minutes of movement. It is necessary to allow the units to warm up at low speeds.
How often should I change the oil in the truck bridge?
In standard operating conditions, replacement is made every 60-80 thousand kilometers or once a year. When working in severe conditions (dust, dirt, frequent towing), the interval is reduced to 30-40 thousand km. Be sure to monitor the condition of the oil visually.
Can I drive with a buzzing bridge?
Short term, yes, to get to the service, but it's risky. Constant operation with a buzzing bridge will lead to painting of gear teeth, the appearance of metal shavings and eventual jamming of the knot, which can block the wheels on the go.
Why is he knocking oil through a sapoon?
This is due to excessive pressure caused by heating the air inside the crankcase or, more often, due to clogged sapuna. Also, the cause may be wear of the seals of the leading gear, allowing crankcase gases, if the ventilation system does not cope.
What is the best oil viscosity for winter?
For winter, it is recommended to use synthetic oils with low freezing point, for example, 75W-90 or 80W-90, depending on the recommendations of the bridge manufacturer. This will ensure normal circulation of the lubricant during cold start.