Document wDqdEB9wXd11eZpGJ32O4O3mB

HEAVY DirH ^ | CORPORATION . SERVICE j .. . V BULLETIN AMERICAN BRAKEBLOK DIVISION BULLETIN NO. 7 BRAKE BALANCE - WHY IT IS SO BASICl Safety has rightfully gained the headlines of late and it has application equally to all road vehicles - the car, truck, trailer and bus. Attention is now being focussed on vehicle safety because of today's mounting accident rate -- it is alarming. The importance of being able to stop the vehicle safely from all speeds is today concerning the maintenance department of all fleets. Recognizing the skyrocketing of insurance rates as the result of an accident motivates fleet operators to be ever more vigilant these days to see that only a safe vehicle is put in service. No vehicle can truly brake safely if the brakes are not properly balanced, it is essential, therefore, that the first objective in brake servicing should be in the direction of attaining and, yes, retaining true brake balance throughout the brake system. At present there are increasing numbers of multi-axle vehicles, doubles and even triples in service. This emphasizes the importance of having the brakes in balance^ _ What do we mean by brake balance? It is the prescribed distribution of the brake load between all the brakes on the vehicle in relation to their designed capacity. Ideally, all brakes on the vehicle or train should reflect brake temperatures nearly equal if they are all working relative to their designed capacity. Brake temperatures readily serve as a telltale of the relative degree of the brake balance. Why is brake temperature so important? It is because brake temperatures are a direct indication of the amount of work being done by each brake. Wide variations in temperature from one brake to another on the same vehicle is a sure sign of unbalanced brakes. This should signal the need to investigate the cause or causes. Abnormally high brake temperatures, especially when they are at wide variance with the temperatures of the other brakes are clues to brake problems. Sustained high temperatures lead to brake fade, rapid lining wear and, in some cases, complete lining decomposition, as well as damage and failure to brake components including the brake drum. In reality, there is no better means of viewing brake performance than evaluating the brake temperatures, their balance and distribution in relation to the designed capacity of the brakes. What causes high brake temperatures? Brake temperatures are directly related to the amount of work performed by the brake. It therefore follows that the more energy being absorbed, the higher the temperature. Temperature variations can result when some brakes do not accept their full share of the work -- this means that the other brakes do more than their share, and, as a result, are overworked. SPNY 005972 SCF-ABEX-0043 BULLETIN NO. 7 Page 2 Brake drums play a very important part in the control of brake temperatures since they represent the other member of the friction pair. Brake balance calls for drums of the same manufacturer and design on all the axles. A light weight drum will heat faster than a heavier one under the same braking conditions. This is why the wall thickness of the drum must be considered, and, in this respect, why a limit is set on the amount of metal that should be removed from the drum wall also why drums on the same axle must be mated in diameters. An unbalanced brake can lead to uneven tire wear as well as greater stress, wear and damage to other components. For the brakes on a vehicle to be truly safe, it is imperative that all of the brakes on a vehicle be capable of operating at their designed capacity. One of the all important guidelines to follow with consistency when servicing brakes is that the output of the brake must reflect the designed effectiveness level of the brake system. This means that the brake repairs must be thorough and include the complete brake system. This important concept of brake balance is not to be confined to the period of reline but should govern all interim services to the brake system. The goal should be the retention of the brake balance for the duration of the lining life. The optimum in both performance and economy is only attainable when all the brakes are performing equally in relation to their designed capacity. . The selection of the proper friction material is basic to good balance. The lining should be of the same manufacturer and formulation on all axles of the vehicle to eliminate introducing any possible variable. Have balance uppermost in mind when servicing brake systems as all brake components fall in this category. The brake input balance affects the output and brake temperature balance. Don't overlook any brake component -- each and every part of the brake system is important and commands attention. Their inspection and replacement have a significant bearing on brake balance. Patrick J. Meade Technical Service Engineer SPNY 005973