Understanding Brake Lining Material Selection

When choosing a material for brake lining, several characteristics are carefully considered to ensure effective and safe braking. The question asks for the characteristic that is NOT typically desired or considered a positive attribute when selecting brake lining material.

Desirable Characteristics for Brake Lining Materials

Let's examine the options and determine if they represent desirable characteristics:

• It should not be affected by moisture and oil: This is a crucial characteristic. Brake linings are exposed to environmental factors. If their performance degrades significantly in the presence of moisture or oil, it compromises braking safety. Therefore, resistance to moisture and oil is a desirable trait.
• It should have low wear rate: A low wear rate means the brake lining material lasts longer, reducing the frequency of replacement and maintenance costs. High wear rate is undesirable. So, low wear rate is a desired characteristic.
• It should have high heat dissipation capacity: Braking generates significant heat due to friction. If the brake lining material can effectively dissipate this heat, it helps prevent brake fade (loss of braking power at high temperatures). High heat dissipation is a very important desired characteristic.

Identifying the Undesirable Characteristic (The EXCEPT Case)

Now let's look at the remaining option:

• It should have low coefficient of friction with maximum fading: This describes highly undesirable properties for a brake lining. The coefficient of friction ($\mu$) is a measure of how much friction exists between the brake lining and the brake drum or disc. A high coefficient of friction is needed to create sufficient braking force. A low coefficient of friction would result in poor braking performance. Furthermore, "maximum fading" means the braking power decreases significantly at high temperatures, which is a dangerous condition. Therefore, having a low coefficient of friction and maximum fading is explicitly NOT a desired characteristic for brake lining material selection. This is the characteristic that is the exception to the selection criteria.

Based on this analysis, the characteristic that is EXCEPT considered while choosing a material for brake lining is having a low coefficient of friction with maximum fading, as this would lead to ineffective and unsafe braking.