MGF/TF Brake Options

Brake Fade

Is brake fade a problem on a standard road-going MGF? No, not really. It is only when you take your MG to a track and give it some real 'welly' do the standard brake's inherent weaknesses become exposed. So for those track day warriors, read on!

Brake fade can occur in two ways, both of which are caused by excessive heat:

Pedal fade occurs as the result of the brake hydraulic fluid boiling in the calipers. It is characterised by the pedal feel getting spongy and travelling closer to the floor. The sensation is somewhat similar to the feel that the brakes have when they need bleeding.

Pad fade occurs when the friction between the pad and rotor is lost as a result of the pad temperature exceeding its peak operating temperature. The pedal feel remains firm, but the car is just not slowing down no matter how hard you push on the pedal. Therefore pedal pressures increase for any particular given retardation.

How do you prevent brake fade?

Pedal fade can often be eradicated simply by flushing out the old fluid and replacing it with fresh, high temperature resistant, fluid (e.g., replacing OE DOT4 fluid for higher performance DOT5). An important point to note however, is that once the fluid has boiled, it no longer has the ability to resist boiling or aeration, and therefore must be completely flushed from the system and replaced with new.

Unfortunately, all non-silicone based brake fluids are hydroscopic - they absorb atmospheric moisture over time. The more water brake fluid contains, the less resistant it is to boiling under extremis.

If pedal fade reoccurs even with new fluid, then a better grade fluid must be used or steps must be taken to isolate the brake pad heat from the fluid in the calipers.

Pad fade can be overcome as simply as backing off the brakes long enough to allow them to cool. However, the cause of the pad fade must be carefully considered if it is found to be a recurrent problem.

1.    The operating temperature range of the pad. Correcting this problem may only require installing the next higher heat range pad compound. For example, exchanging the standard, original-equipment, road going pads for a fast road pad, such as Mintex's 1144.

2.    Specification of the brake disc, or rotor. If the vehicle is already equipped with a high temperature pad, the next area that requires attention must be brake rotor size and cooling. It is the brake rotor's job to absorb then dissipate the heat generated by applying the brakes (friction dissipates the energy absorbed from motion as heat) - and to keep that heat 'locked' out of the brake pads to prevent them from overheating. Design considerations of the brake rotor include the cooling vents - or vane configuration - rotor mass, surface area and wall thickness. All these factors must be optimised to effectively manage the heat generated. In some cases, to overcome pad fade, a larger or heavier rotor may be necessary. It may also be necessary to install or increase the cooling duct system to provide additional airflow to the rotor. In any case, the system must be configured to effectively manage the brake heat or the consequential fade problems will continue to occur.