What causes ‘brake fade’ and how can I prevent it?
QI took my Renault 19 to the French Alps this year. Coming down a steep incline, the brakes started to become increasingly poor. I know cars used to suffer ‘brake fade’, but I didn’t expect it from a fairly modern Renault. Is this normal, or does the car need attention? The brakes were fine before and have been fine since.
Jim Grebe, Hornsea
AOld brake fluid is the most common cause of a loss of braking under duress. It absorbs moisture over time, lowering its boiling point. When it starts to boil, pockets of gas build up in the brake cylinders and calipers. The pedal may go straight to the floor because it’s compressing gas rather than moving the pistons outwards. Pumping it might temporarily restore some braking action. Stop and allow it to cool at the first sign of this.
Changing your fluid every couple of years will massively reduce brake fade and prolong the life of your braking system. Start by draining the hydraulic reservoir with a syringe. Fill it with fresh fluid and bleed the system through until clean, clear fluid issues from each nipple. Start with the rear left wheel, then rear right, front left and front right. At least one litre of fluid will be needed to flush the whole system thoroughly.
Check that all your brakes are operating correctly and none are stiff or seized, which will make the others work harder. Do not rely on a recent MOT – the roller test misses defects that appear in real-world usage. Make sure there’s plenty of meat on the pads and shoes and set manual shoe adjusters. Also check the adjustment of the handbrake.
Traditional so-called ‘brake fade’ is caused by hot drums.
The drum loses heat through the wheel and hub, so the side of the friction surface nearest the wheel runs cooler than its inner edge. This causes the surface to expand unequally and presents a curved surface to the brake shoes rather than a flat one, so there’s almost no contact area. The pedal feels hard with little travel. Pumping it will have no effect. Front brakes generally dissipate at least twice as much heat as the rears, so these are likely to suffer first. Front disc brakes don’t suffer from this – hence their universal adoption during the Seventies.
Friction material matters, too. Most pads or shoes can be considered adequate under most circumstances, but some lose their efficiency quite markedly in more extreme use. The brakes dispose of the car’s kinetic energy as heat – and if you’ve ever tried to stop a car gently rolling away, you’ll appreciate how much energy is involved in stopping one from hurtling down a mountainside. There’s a big difference in the ways different grades and qualities of friction material behave at high temperatures. The manufacturer EBC, for example, offers a number of materials whose characteristics vary according to their use.
Motorsport materials are likely to feel rather insensitive when cold and come into their own only when hot, so they’re not a cure-all fix. Small firms offer relining services.
You can discuss your requirements with them and they’ll fit the most suitable material.
Finally: how’s your driving? Many modern motorists descend hills entirely on the brakes, which is a short-sighted policy for long descents. Put the car in a lower gear and let the engine control the speed. Second gear’s usually a good choice for steep hills. Don’t worry about running the engine at high rpm. As long as you’re not in a hurry to get to the bottom, it should be enough to apply the brakes occasionally to rein in the speed.