OUR WINNING RANGE

DRUM BRAKES

Oom Japie Bok featured on this page many years ago and we’re glad to report he’s still with us. You may remember the time he foolishly neglected the goat-farmer’s golden rule: never bend down when there are goats nearby. He was walking across one of his neighbour’s elds and bent over to tie his shoelaces when a young Billy goat saw this enticing target and charged. The impact sent Oom Japie ying and, while he suffered excruciating pain, the fact that goats have two horns and a strong sense of symmetry did save his vital offspring-producing organ. The common consensus was that Oom Japie should be thankful his neighbour did not farm unicorns.

Oom Japie recently did what I would like to do: he bought an old Volkswagen Beetle with the intention of restoring it. The Beetle is the rst car that could be driven absolutely at out the whole day without suffering overheating or any other malfunction. Oom Japie’s Beetle is in a fair and drivable condition, but one of the rear wheels recently locked up, so we had to tow it in.

Hennie stripped the wheel and discovered one of the brake pistons had pulled out of its cylinder and was jamming the linings against the drum. This happens when the linings are worn very thin or the interior of the brake drum has been machined too often. It can also be a combination of both conditions. Hennie measured the drum-wall thickness, compared it with values in our never-discarded Beetle workshop manual and realised the brake drum had been machined to beyond a safe limit. Hennie then opened the other rear-wheel brake assembly and found that it was close to initiating the same catastrophe.

We had to nd two used brake drums in good condition because Oom Japie would struggle to afford two new ones. Japie was dispatched to the scrap yard to unearth suitable callipers and drums (the latter should preferably not be too oval). If you nd slightly oval units are the only ones available, the walls should at least be thick enough to allow enough machining to correct the oval shape. Unfortunately, Japie could not nd any suitable drums, so we had to buy new aftermarket ones. Imported from China, they were reasonably priced and, while not suitable for a concourse car, would be good enough for an old vehicle used every now and then. The wheel cylinders, pistons and seals, as well as the shoes and linings, were available from brake-repair workshops.

Japie asked the obvious question: “Why do brake drums go oval?” This usually happens when the driver applies the handbrake immediately after the brakes are hot from frequent usage. As the drums cool down, the free part of the drum is able to shrink more than the part that’s restricted.

DISC BRAKES

I don’t see Wayne the Whippet very often; he’s so skinny that you can easily miss him. He also displays the same nervous energy as his canine namesake. As a professional blogger, he’s one of those new opinion makers who have made large sections of the Internet extremely boring. Don’t ask me what he blogs about.

Whippet recently bought a 2009 Ford Fiesta and brought it to our workshop for a check-up. We gave it the usual service and August took the car out for a spin. He reported that the brakes squealed and were spongy.

An anti-lock braking system (ABS) needs clean brake uid every two or three years, so August drained the old brake uid, ushed the system and lled it with fresh uid. Following the procedure recommended by Ford, he also bled the brakes using our pressurised equipment. With ABS, it is necessary to use a particular sequence for opening the bleeding ports at the wheels, starting with the wheel furthest from the master cylinder and then following the sequence as given in the manual.

August tested the brakes again and found the sponginess was still there. He then jacked up the car and examined all the pipes and hoses while Japie kept on applying and releasing the brakes. The real culprit turned out to be a brake hose that ballooned when the brakes were applied, most likely due to old age. All similar hoses were replaced.

Brake squeal is always present, according to a well-known brake component manufacturer, but the frequency is so high humans cannot hear it. This phenomenon explains why dogs know when their master is approaching home. They can hear when the car brakes at the corner close to home (each car will have its own frequency). Vibrations usually cause brake squeal from the discs, the pads or the calliper, brought on by material roughness, dirt or poor-quality brake pads. In many cases, a new set of discs and the correct pads will increase the frequency so that it becomes inaudible. If the noise is still there, a small amount of high-temperature brake grease applied to the backs of the pads may help. The shims and anti-rattle clips usually provided should always be present.

In this case, we tted the correct (and rather expensive) Ford brake pads and the noise was gone. Whippet whimpered happily when we return the Fiesta.

BATTERY DRAIN

My car’s tracking system drains the vehicle’s battery within a few days if it’s not driven. The battery is new and of a higher quality than OEM specification. An auto electrician has advised me to replace the alternator because it is not charging the battery. I had the battery fully charged at a specialist and afterwards it found the alternator does charge the battery sufficiently.

The Casebook article in the June issue mentions “a car’s alternator is not designed to completely charge anything but a brand-new battery”. Do you mean an alternator cannot fully charge a battery if it is not new, or can the alternator not charge a used battery at all? K BEKKER Via email Firstly, the current drawn from a tracking device should not drain a battery within a few days. We know many tracking devices also have their own power sources (batteries) to solve the problem of battery drainage. Therefore, either the device is faulty or the charge drain is coming from somewhere else. An easy way to check is to remove the battery’s negative terminal and connect an amp meter between the negative pole of the battery and the ground terminal. When the vehicle is parked, the parasitic amp draw should be close to zero with any reading higher than 0,1 A problematic. You can remove the fuses one by one until you see the amp reading drop to zero, pinpointing the system to blame.

Do not read too much into the statement that an alternator can charge only a new battery. We spoke to Garageman and he told us a starter battery is not supposed to drain completely. If this happens a few times, the battery’s maximum capacity is lost (through damage) and an alternator cannot recover this lost capacity. In general, an alternator can charge a battery close to full capacity if the battery is in good health.

A bench charger has finer control than a vehicle’s alternator system and will be able to approach the maximum charge capacity when hooked up for a long time.

DUAL-CLUTCH vs. TORQUE-CONVERTER

I just finished reading your review on the BMW M5 and Mercedes-amg E63 S and have a question: manufacturers seem to be moving away from dualclutch transmissions. Is this a step backwards, or are torque-converters more practical given the high power outputs? SELLO HLALELE Centurion We think there are a few reasons why manufacturers are moving away from dual-clutch transmis- sions in the luxury sports-sedan segment, including: • Torque-converter transmissions are now almost as fast as dual clutches. • They may be more durable in vehicles destined to do high mileages and given the amount of power (and torque) on tap. • A torque-converter transmission’s low-speed stop-start traffic behaviour is much smoother, with a more predictable creep function. Dual-clutch transmissions can be snatchy during low-speed manoeuvring.

ROLLING-START QUESTION

When a vehicle’s battery is flat and the engine cannot start, it is sometimes still possible to push-start the car. My question is whether a vehicle needs a battery at all to start. Would the alternator not provide current

necessary to start the engine during a rolling-start scenario? JEREMIAH MNISI Hazyview The reason a car’s engine starts during a rolling start when the battery is flat is because the latter still has enough energy to run the ignition system (and fuel injection) but not enough to crank the engine with the starter motor while running the ignition system. Attempt a rolling start (push start) without a battery and the alternator may not be spinning fast enough to provide enough current for the ignition system. The battery also functions as a buffer to the electrical loads and helps prevent voltage spikes in the system. Therefore, we would not recommend trying to start a vehicle without a battery fitted. Some off-road motorcycles (and lawn mowers) can function without a battery because their magneto-ignition systems are designed to run without one.

TYRE LIFE?

I seldom drive my Mazda 323. My vehicle’s tyres are now nine years old with the tread depth still legal. Should I change my tyres because of their age? My mechanic says the rubber gets hard and it is not so safe anymore? ELSIE DE JAGER Johannesburg Tyre brands state a tyre’s life is usually five years after the date of build. This, however, is a conservative estimate and it will last longer in ideal conditions, such as little contact with sunlight and correct pressures. It is true the rubber compound may become hard with age and even form hairline cracks. It will also have a negative impact on braking and handling performance, especially in the wet.

We would agree with your mechanic, as the tyres may be a safety risk. We realise it’s expensive but they are a critical safety item. Phone round for prices but fit a reputable brand rather than a cheap, unknown one

MONDEO STUTTER

I drive a 1998 Ford Mondeo 2,0-litre 16-valve Zetec. It has a misfire and jerk when I put my foot on the accelerator. After the stutter, the engine picks up again. What can be wrong? CHRISTO BREWER Cape Town A stutter occurs when the combustion process is not optimal at the speed and load point. There can be many reasons that are all air, fuel, compression or spark related. We’d follow these investigative steps: • Make sure the vehicle is fully serviced, including all filters, spark plugs and engine oil. • Ensure there aren’t leaks on

the intake piping. • Clean the throttle body. • Drain a sample of the fuel from the filter to check for water content (water is heavier than fuel and lies at the bottom). • Check if the fuel pump supplies enough fuel. Disconnect the fuel pipe and catch the fuel in a container when the ignition is switched on. • Investigate the spark plugs to see if any plug is a different colour. That may point to a problem with a single cylinder. Excessive black deposits on the electrodes may indicate incomplete combustion, oil being burned or a rich fuel mixture. • While the plugs are out, do a compression check and compare to factory specification. A cylinder that is down on compression may point to a mechanical problem with the piston, rings, cylinder or a valve-seat issue. • Check the plug leads for damage and the rest of the electrical system for obvious problems like cracks in coils, etc. • The main misfire culprits are a faulty/dirty mass airflow sensor (MAF) in the intake and lambda (or O ) sensor in the exhaust, if fitted. To test if it’s any better, you can disconnect the MAF sensor and drive “open-loop”. The air-fuel ratio can be checked in the exhaust by using a gas analyser.