J.L. Classics

Classic Tips. MG Restoration

How to Prevent the Average Classic Car Breakdown

Most cars break down at some time but the good news for classic car owners is that where their cars are concerned the original design has clearly stood the test of time.There is no reason, therefore, providing the car is maintained & checked regularly,it should suddenly prove to be unreliable.

The durability of some components over their long service life does cause problems. It is our experience that out of all roadside breakdowns over half will be as a result of one of the following


1. Failure of the electrical fuel pump is the most common cause. Check the power supply then check to see if the pump has a good electrical earth. This may be a black wire from the pump to your vehicle body or it may be a direct contact with the pump body to chassis. If your not sure put in a test wire to see if it makes a difference. Take care not to create any electrical sparks near petrol !

2. A carburettor jet blockage due to rust sediment coming though from the interior of the petrol tank. If you have twin carbs only one has to be blocked and it will throw out the running. To find out which one - split the linkage between the two, then by hand rev the engine upon each carb. If it runs well upon just one and dies upon the other you will know which one to clean. Where the carbs are upon a common manifold it is possible to drive the car with just one carb connected. An engine will run much better with only one carb working correctly that with it being linked to a second that is blocked. I drove a TR3 back from France with just one carb out of the two connected.

3. A badly corroded petrol tank. All petrol tanks get water in them. This rests upon the bottom of the tank and can rust the tank from the inside.Few of us ever check their petrol tanks condition but it must not be ignored.

4. Perished/split rubber fuel pipes. These are sometimes hard to detect. A poorly connected joint or split between the petrol tank and pump may not leak petrol but could have air being sucked into it by the pump. Your tank has petrol, petrol pump is working but not enough fuel to run the engine - look for an air leak before looking for a blockage.

TOP TIP - Always have inline fuel filters in an old cars petrol supply system. It saves so many problems.


1.Again the primary cause is the failure of the H/T leads. (spark plug leads) The effectiveness of H/T leads cannot be solely judged by their appearance since they break down internally.

2.The low-tension distributor contact points are rarely at their optimum setting due to distributor spindle wear and or lack of regular physical checking.
Poor contact point condition and setting gives a range of the most frustrating symptoms from not starting to poor running and high fuel consumption.

3. Low-tension circuit electrical connections are often considered to be in good condition because they can be seen to be connected. Poor electrical conductivity due to dirt, corrosion and loose fitting may show as an intermittent fault which is difficult to trace.


1.The majority of Classic Cars are used infrequently. The car battery is an item, which performs best when it has some chemical activity due to charging and discharging. We often get told that a particular battery is virtually new but does not work. The owner fails to mention that neither their car or battery has been used for six months. The answer is to start and run the car engine at frequent and regular intervals.

2.The electrical leads and terminals do cause problems. Lack of electrical power may not be due to a poorly charged battery. The condition and fixing of all leads and terminals is important. The engine earth lead, for example, is often overlooked being hidden within the engine bay.

3.A vehicle's external lights ought to be of a reasonable intensity. Differing intensity of lights or sidelights going out when the indicators are put on is usually a problem relating to the bulb holder not being effectively earthed or rusty bulb holders.
Traffic Indicator lights are intended to automatically go on and off at regular intervals. Older vehicles can have trafficator lights that operate at ANY speed (apart from an acceptable one). If your flasher unit is of the three-pin type this can be replaced with a very similar electronic three-pin unit which provides a regular speed indication under all circumstances (it also has a blown bulb indicator built in).
Driving your classic at night can be made safer by upgrading the light output of the headlights. Changing original sealed beam units to quartz halogen bulbs with more efficient reflectors/ lenses is an upgrade never regretted. A conversion kit is available.This is for for R/H or L/H drive vehicles with or without pilot light.

The majority of the causes can be avoided easily by preventative maintenance.

UPDATE NEWS FLASH ! The vast majority of contact points, condensers and rotor arms are imported from one manufacturer - by the millions. Replacing your rotor arm, contact points or condenser might well sort the immediate fault UNTIL the replacement item then fails ! Be aware all major suppliers still have these faulty items in stock. In the last 12 months we fell fowl of this with three of our cars. I am reluctant to put names to suppliers but these items are retailed under many branded names. This is well known within the Classic Car trade. You may phone for help/details.

If you would like us to check these areas for you and show you what to look for contact us for an appointment. Listed are some of the more common faults we are happy to help out with more trying problems.

Explaining axles also called Diffs (differentials units).
The differential has three functions. It takes the drive from gearbox via the prop shaft to the rear wheels AND
1/ Takes the drive through a right angle, from down the vehicle to across it. 2/It allows for both rear wheels to be driven at the same time or just one of them – this is so that the vehicle can go around corners. The outside wheel upon a bend has a greater distance to travel than the inside one, hence it travels at a faster speed
3/ It changes the gearing from the gearbox to the rear wheels. For example a 3.7 to 1 diff turns only once when the drive into it turns 3.7 revolutions.

Speedometers are calibrated to match the differential when the vehicles are built.

Tyre size also impacts upon the final gearing and speedometer readings. A low-profile tyre might have a smaller diameter than the original tyre. A smaller wheel has to rotate more often than a larger wheel; to go the same distance. This is another form of gearing. There are many free programs upon the internet which will compute these ratios for you if you are changing from standard wheels/tyres

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