Ask the Mechanic

WHY DOES MY CAR FAIL TO BRAKE?

Hello Paul, my Toyota Passo delays to brake. My mechanic has fitted new brake pads, replaced the brake master cylinder and bleeder several times and checked that there are no leakages on the brake pipes. However, the brake pedal does not have normal pressure and the car delays to brake. What could be the problem?

Kamabare

Hello Kamabare, during your brake system service, you seem to have ticked all boxes except the last one that says change all the brake fluid before bleeding to evacuate air bubbles. Car brakes are important for slowing down or stopping the vehicle. Whereas we usually replace the brake pads or other damaged brake system components such as calipers or master cylinders, often, motorists and their service providers tend to neglect brake fluid service.

Brake fluid is designed to provide hydraulic pressure, which makes it easy for us to slow or stop the 0.5 -1 tonne vehicle load by gently stepping on a small brake pedal. Brake fluid is composed of anti-oxidants and corrosion inhibitors to prevent corrosion, which is harmful to the brake system.

Brake fluid is designed to operate at a higher boiling point in order to effectively transfer heat away from the very hot brake components. Brake fluid also works as a lubricant to prevent frictional damage.

Why replace brake fluid?

Brake fluid, like any other hard working car fluid, will age overtime. The common brake fluids we use DOT 3 and DOT4 are hygroscopic (attract moisture or water) and with continued use, the brake fluid accumulates water. This alters its chemical composition and performance.

As brake fluid cools, the hot brake components bring deposits and soot, which cause contamination and colour change overtime. Subsequently, the brake performance reduces and some of its components suffer damage from corrosion, poor lubrication and overheating. This is why we must service brake fluid.

When to replace brake fluid

Toyota recommends renewal of brake fluid every 30,000 kilometres or after two years. It also recommends a regular visual inspection of the colour of brake fluid. If it has turned dark or has particles or signs of water presence, it should be renewed.

However, oftentimes, the colour of brake fluid in the reservoir is cleaner than that in the brake lines and brake slave cylinders attached to the callipers of each wheel.

It is better to renew all of the brake fluid (not top up) every two years or 30,000kms, whichever comes first.  The best brake fluid service procedure is with the use of a brake bleeding and service tool which works such as a human kidney dialysis machine.

This tool pressure pumps new brake fluid into the brake fluid reservoir while pumping out and replacing the old brake fluid trapped at each wheel cylinder. This renews the brake fluid as it primes (bleeds) the system to rid it of vacuum.

DOES MY CAR NEED WATER IN THE COOLING SYSTEM?

Hello Paul, I have just bought a Toyota Hiace van and I have a question. I see two coolant containers, one on the radiator and the other white, which is empty. Can I fill it with water? 

Nankunda

Hello Nankunda, the white container with a picture of a radiator on its cap is a coolant expansion tank. It should be topped up to the recommended level with engine coolant, not water.

Reputable engine coolant is designed with additive molecules that prevent corrosion and overheating of the engine while lubricating fast moving parts of the cooling system such as the water pump. I suggest you go to a garage or good service bay and carry out a comprehensive first service inspection since you have just received this used vehicle and may not have its service history.

Start by building your own good service record of all serviceable fluids, filters, belts, hoses, ignition and fuel system components. An inspection of tyre age and condition, lights, brakes, seatbelts and other safety or operational features is also necessary.

WHEN SHOULD A GEARBOX BE REPLACED?

Hello Paul, my mechanic says my Toyota Raum gearbox is not changing gears because it is spoilt and has to be replaced. Is this true?

Muhamudu

Hello Muhamudu, without all the facts at hand such as a full diagnostic or defect report I can only suggest. Generally, when an automatic gearbox fails to shift gears, the cause could range from failure to service the gearbox oil and filter on time, a sudden loss of gearbox fluid due to a severe leak, mechanical damage of internal components (usually due to gearbox oil quality or quantity) or electrical failure. Whichever the cause, I presume your mechanic has inspected the gearbox to rule out the above before drawing the conclusion to replace it.

Automatic gearbox repair would be another option but it is usually defeated by lack of genuine spare parts to do the job or in the event of severe mechanical damage, rendering it not cost worthy to repair. Ask your mechanic to share a detailed defect report and discuss with you clearly why he decided to replace the gearbox.

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