Hi Paul, I read an article about skimming brake discs last week on Thursday. I drive a Toyota Land Cruiser Prado 1994 model.

Lately my brake discs squeak despite replacing the pads. One of the brake repair shops in town recommended skimming the discs. However my mechanic says I should replace the worn out discs. What should I do? Sam Kajubi.

Hello Sam, brake disc rotor skimming is machining the disc surface with a lathe to renew the surface. This is aimed at improving frictional contact with brake pads in order to improve braking efficiency.

The most common cause of damage to brake discs is failure to replace the friction brake pads on time which leads to damage of the discs by metal to metal contact.

Disc damage is in the form of fine or deep ridges all over the surface. This results in poor contact with new brake pads, squeaking and in cases of severe wear cracking of discs during extreme braking.

Brake discs for a Toyota Land Cruiser ought to be skimmed only if they still meet the minimum disc width (front discs 30mm and rear discs 16mm). Skimming brake discs beyond the minimum safe width can reduce braking efficiency (increase braking distance) or lead to failure of the brake discs (cracking) when you brake hard.
Whereas the option to skim the damaged discs may be attractive, the mechanic’s advice that the discs be replaced because they are worn out beyond the minimum disc width, should not be ignored.

What is wrong with my gearbox?

Hi Paul, I drive a second generation BMW X5 E70 with 130,000 miles on the clock. It has been mostly trouble free until recently when the gear shifts started faltering when driving uphill. My mechanic says it might be an electrical fault. I have been told that this gearbox is lifetime and should not be tampered with. What is your opinion? Thank you. Nathan Tumwebaze.
Hello Nathan, ‘lifetime gear box’ is a fallacy or marketing gimmick. It means the car manufacturer expects the gearbox to be service free for the duration with the first owner.

This is usually a period of five years or 120,000 miles (200,000kms) or whichever comes first. After this mileage it is time to carry out long life filter and fluid change or service.
This includes fuel filter, gearbox filter (with gasket) and gearbox oil, transfer case oil, brake fluid as well as long life radiator coolant.

The availability of a BMW gearbox service kit (oil, filter and gasket) confirms that this service should be done at some point. Please note that your ZF gearbox filter is incorporated in the oil pan or sump cover.

You must service the gearbox with the approved ZF Automatic gearbox fluid. A special procedure should be followed to drain and refill the gearbox.

Where can I buy a 2003 Land Rover Discovery?

Hi Paul, does the 2003 Land Rover Discovery series ii have a 2.7 or 2.5 litre engine? Is it diesel or petrol and where can I buy it online? Would you recommend a diesel or petrol engine? Aheebwa.
Hello Aheebwa, the Land Rover Discovery (Disco) series ii (L318) built 1998-2003 comes with two petrol engines (4.0 litre and 4.6 litre) and one diesel engine (2.5 litre turbo intercooled).

The 2.7 litre diesel is for the third generation (L319) built between 2004 and 2009. Land Rover Discoveries with 2.5 or 2.7 litre turbo diesel engines are mostly found on UK car selling websites. Japanese online car sellers will only have the 2.5 litre diesel Discovery generation i (1995-1998).

However the petrol powered 4.0/4.6 litre are readily available in all generations from both Japan and the UK. If you are going to buy the turbo diesel 2.5 or 2.7 litre Disco i/ii from the U.K you will need to confirm that it does not have corrosion damage from the ‘winter road salt’.

You may need a third party person to check and confirm mileage and corrosion status.

Why are my front tyres smaller than the rear ones?

Hi Paul, I have bought a BMW X6 but have noticed that the rear tyres (315/35/20) are bigger than the front ones (275/40/20). Is that a good idea and does it have any advantage? Will it not cause a nightmare when I am buying new tyres? Bernadette Karungi
Hello Bernadette, it’s common for racing and high performance cars to fit bigger tyres on rear axles.

High performance vehicles such as BMW need maximum traction and usually suffer from over steer (a car turns more than the driver wants it to turn) which affects handling.

Designing the car with wider tyres on the rear axle improves surface grip, which gives better road holding when performing high speed maneuvers. Wider rear tyres are used by car designers to induce under steer as a means to counter the over steer caused by high speed driving.

Most car tyrer dealers are used to this car tyre profile and will stock different tyre sizes that meet your car needs.

Just avoid mixing them up. If in doubt consult the BMW user handbook or check the fuel flap or driver A pillar post for recommended tyre sizes for the front and rear axles.

Hi Paul, I read your articles in the Thursday Daily Monitor. I own a Toyota Spacio 1.8 litre petrol, which I drive a lot on the highway.

Which fuel can help to improve my engine power? Can I fit a 1.5 litre smaller engine to enjoy better fuel economy?

I have noticed that the exhaust pipe has black soot, what could be the cause?
Sula Makumbi.
Hello Sula, in order to improve the engine power of your Toyota Spacio you can fuel it with the high octane Shell V-Power petrol. Higher octane fuel has the effect of slow burn during combustion, which helps control timing of detonation.

This has the effect of producing bigger bursts of engine power, better efficient performance and engine protection due to reduced cylinder knock. Basically, higher octane fuel will bring the best out of your small petrol engine.

I should hasten to add that the fuel benefits of high octane petrol will only be realised if your engine lubrication (oil and filter) and ignition (spark plugs and air cleaner) systems’ service is upto date.

I have noticed that you have black soot in your exhaust pipe which might be a sign of poor fuel combustion either due to a dirty air cleaner element or worn out spark plugs.
If you are a frequent highway traveller downsizing the Spacio engine from 1.8 litre to 1.5 litre may not necessarily improve your fuel economy.
A smaller 1.5 litre engine may not be suitable for the load or speed you need to drive on the highway. As such, your acceleration may keep the revolutions of the 1.5 litre engine higher than those of the 1.8 litre petrol engine.
Higher engine revolutions mean more fuel consumption. I suggest you retain the 1.8 litre engine, use high octane petrol to give you the power you need and keep the service up to date.