S-class W202 Mercedes
1993-2000 of release
Repair and car operation
- 1.2. General information
+ 1.7. Safety systems
+ 1.8. Salon equipment
+ 1.9. Driving
1.10. Engine cowl
1.11. Ventilation block, conditioner
1.12. Some councils upon car purchase
1.13. Changed numbers
1.14. Purchase of the old car
1.15. Durability of the car
1.16. About parallelism of bridges of the car and the trailer
+ 1.17. Preparation of the car for winter
+ 2. Maintenance
+ 3. Engines
+ 4. Greasing system
+ 5. Cooling system
+ 6. Heating, ventilation
+ 7. Ignition system
+ 8. Fuel system
+ 9. Transmission
+ 10. Running gear
+ 11. Steering
+ 12. Brake system
+ 13. Body
+ 14. Electric equipment
+ 14.2. Electroschemes
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For everyone engaged in operation of lorries is not a secret that the exact centering of an operated axis increases service life of tires, increases stability of movement of the car and facilitates management of. Two important reasons because of which it is necessary to support parallelism of leading bridges of the car and trailer axes are also well-known: service life of tires and fuel consumption. But there is also the third factor to which sometimes do not pay attention, but it, maybe, the most important. This factor, safety is.
Every time when coaxiality of any detail is broken, regardless of, whether is it in the engine, transmission or a suspension bracket, there can be unsafe traffic conditions. Besides, there is an increasing possibility of "folding" of a road train at movement on dangerous roads if dual axes of the trailer are not parallel. If all axes of a road train are parallel, he will make rectilinear movement on the road. But if axes of the trailer are not perpendicular a longitudinal axis of a road train, the trailer will tend to move in that direction to which its axes are perpendicular. It complicates driving and causes a lateral proskalzyvaniye of tires in addition to advance. There is a premature wear of back tires and additional wear of lobbies. Certainly, this proskalzyvaniye of tires caused by not parallelism of bridges, will cause increase in fuel consumption.
The car with not parallel bridges undoubtedly much is heavier for operating on dangerous roads. If not parallelism is rather great, the car can become dangerous even on the good road as the driver should fight against a tendency of such car to turn constantly.
Parallelism of dual bridges should be checked each time when the car arrives in a workshop for suspension bracket maintenance. Such check should be made no more than through 50 thousand km of run of the tractor, and the trailer – from 160 thousand to 200 thousand km on the corresponding equipment.
Need of the following centering of axes can come before the expiration of 160 thousand km of run. It can be caused by small blows (when moving through a bordyurny stone or blow about an angular rack) or damages at collision. Even usual wear of plugs of jet bars of a suspension bracket on one party of the car can cause not parallelism of bridges.
At left foreign driving of a wheel of the right board perceive more shock loadings, than wheels of the left board as they move on roughnesses at roadsides more, and also as a result of redistribution of weight of the car on boards because the majority of roads has slightly convex profile. Usual wear of plugs or replacement of a jet bar can cause not parallelism of dual bridges. Undoubtedly that check of parallelism of bridges at any repair work should become a rule.
Tires with a radial cord are more sensitive to not parallelism of bridges, than tires with a diagonal cord for all types of axes and suspension brackets. Symptoms of wear of tires with a radial cord often appear after 16–32 thousand km of run, and at tires with a diagonal cord – after 80–92 thousand km of run.
For tires with the radial cord, established on operated axes, wear of humeral zones from the internal and external parties is characteristic. At turn of edge of a protector aspire to rise, as unlike the tires established on leading bridges, in this case there is no the force keeping the plane of contact of the tire with a roadbed. This wear usually does not influence durability of the tire so it is observed only on the first 0,79 mm of width of a protector.
Not parallelism of bridges usually results in cross-section wavy wear of the tire. If bridges are not parallel and the trailer tends to move aside from a longitudinal axis of a road train, there will be a non-uniform wear of the internal and external tire at a dual oshinovka or internal and external parts of a protector at an unary oshinovka. It causes proskalzyvany tires and its wavy wear which is very similar to wear of the tire, established on an operated axis. Result of such non-uniform wear of a protector can become "skalpirovany" tires.
Forms of wear of the tire with a radial and diagonal cord are various. For example, at the first of them both too big, and too small pressure of air brings besides to the wear of a protector about an internal and external humeral zone. At the second at an elevated pressure of air wear of the central part of a protector increases, and at the lowered pressure of air – internal and external edges of a protector. This wear usually is quicker found in tires with diagonal, than with a radial cord. The unary wide-profile tire has the same spot of contact to a road surface, as both dual tires of a usual profile.
The wear caused by not parallelism of bridges, possibly, will not appear on unary wide-profile tires as quickly because they wear out on turns, than dual tires of a usual profile less. Nevertheless they are more expensive, so check of parallelism of bridges at installation of unary wide-profile tires is obligatory.
At new trailers it is necessary to check parallelism of installation of their axes. However it is necessary to remember that this adjustment will not be the last. There is a period of grinding in of details, especially at application of a four-spring suspension bracket.
After small run of the chassis it should be checked, as some shift to the right because of gaps in earrings is possible. Usually shift of a longitudinal axis of the chassis (concerning a bridge axis) increases during trailer service life. Than run of the trailer, subjects bigger wear more arises in directing devices of a suspension bracket or earrings.
While wear of tires and the fuel consumption, depending on preservation of parallelism of bridges, can be defined, the traffic safety being even more important factor to measure not so easily. Regular checks and adjustments of parallelism of bridges only with a view of safety considerably reduce the additional expenses connected with damages, failures and idle times of cars.