BMW 3 series E30

Since 1983-1994 of release

Repair and car operation

14.5. About parallelism of bridges of the car and the trailer

THE GENERAL DATA

For everyone engaged in operation of lorries is not a secret that the exact centering of an operated axis increases service life of tyres, raises stability of movement of the car and facilitates management of it. Also well-known two important reasons because of which it is necessary to support parallelism of leading bridges of the car and trailer axes: service life of tyres and the fuel expense. But there is also a third factor to which sometimes do not pay attention, but it, maybe, the most important. This factor, safety is.

Every time when it is broken соосность any detail, without dependence from, 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 the lorry convoy at movement on dangerous roads, if dual axes of the trailer непараллельны. If all axes of the lorry convoy are parallel, it will make rectilinear movement on road. But if trailer axes are not perpendicular a longitudinal axis of the lorry convoy the trailer will tend to move in that direction to which its axes are perpendicular. It complicates driving and causes lateral проскальзывание tyres in addition to advance. There is a premature deterioration of back tyres and additional deterioration of lobbies. Certainly, it проскальзывание the tyres, caused непараллельностью bridges, will cause increase in the expense of fuel.

The car with not parallel bridges undoubtedly much is heavier for operating on dangerous roads. If непараллельность it is great enough, the car can become dangerous even on good road as the driver should struggle constantly with the tendency of such car to turn.

Parallelism of dual bridges should be checked up each time when the car arrives in a workshop for suspension bracket maintenance service. Such check should be made no more than through 50 thousand in km of run of the tractor, and the trailer – from 160 thousand to 200 thousand in km on the corresponding equipment.

Necessity of a following centering of axes can come before the expiration of 160 thousand in km of run. It can be caused small blows (at moving through бордюрный a stone or blow about an angular rack) or damages at collision. Even usual deterioration of plugs of jet bars of a suspension bracket on one party of the car can cause непараллельность bridges.

At link sided driving of a wheel of the right board perceive more than shock loadings, than a wheel of the left board as they move on roughnesses on roadsides more, and also as a result of redistribution of weight of the car on boards of that the majority of roads has slightly convex profile. Usual deterioration of plugs or replacement of a jet bar can cause непараллельность dual bridges. Undoubtedly that check of parallelism of bridges at any repair work should become a rule.

Tyres with a radial cord are more sensitive to непараллельности bridges, than the tyre with a diagonal cord for all types of axes and suspension brackets. Symptoms of deterioration of tyres with a radial cord often appear after 16-32 thousand in km of run, and at tyres with a diagonal cord – after 80-92 thousand in km of run.

For tyres with the radial cord, established on operated axes, deterioration of humeral zones from the internal and external parties is characteristic. At turn of edge of a protector aspire to rise, as unlike the tyres established on leading bridges, in this case there is no the force keeping a plane of contact of the tyre with a roadbed. This deterioration usually does not influence durability of the tyre so it is observed only on the first 0,79 mm of width of a protector.

Непараллельность bridges usually leads to cross-section wavy deterioration of the tyre. If bridges непараллельны and the trailer tends to move aside from a longitudinal axis of the lorry convoy, there will be a non-uniform deterioration of the internal and external tyre at doubled ошиновке or internal and external parts of a protector at unary ошиновке. It causes проскальзывание tyres and its wavy deterioration very similar to deterioration of the tyre, established on an operated axis. Result of such non-uniform deterioration of a protector can become "скальпирование" tyres.

Forms of deterioration of the tyre with a radial and diagonal cord are various. For example, at the first of them both too big, and too small pressure of air results besides to the deterioration of a protector about an internal and external humeral zone. At the second at air elevated pressure deterioration of the central part of a protector increases, and at the lowered pressure of air – internal and external edges of a protector. This deterioration usually is fast found out in tyres with diagonal, than with a radial cord. The unary wide-profile tyre has the same stain of contact to a road surface, as both dual tyres of a usual profile.

The deterioration caused непараллельностью of bridges, possibly, will not appear on unary wide-profile tyres as quickly because they wear out on turns, than dual tyres of a usual profile less. Nevertheless they cost more expensive, so check of parallelism of bridges at installation of unary wide-profile tyres 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 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 should be checked up, as some shift to the right because of backlashes in earrings is possible. Usually displacement of a longitudinal axis of the chassis (concerning a bridge axis) increases during trailer service life. The more trailer run, the больший deterioration arises in directing devices of a suspension bracket or earrings.

While deterioration of tyres and the fuel expense, depending on preservation of parallelism of bridges, can be defined, the traffic safety which is 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.