How your car works - Manual & Automatic Gearboxes

What's the difference between Manual and Automatic?
There are many different types of transmission fitted to the vehicles on our roads today. Manual Transmission (4, 5 and 6 speed), Automatic Transmission (3, 4 and 5 speed) and Semi-Automatic Transmission. With such a variety how do you best decide which one is for you? Well, It depends on what sort of driving you do and where it is that you do it. For example, you drive to work in a city in rush hour, the only type of gearbox to have in your car is an Automatic. If on the other hand you prefer the arduous task of constantly holding the clutch pedal down, then the Manual type is for you. But hold on, there is something in between, a Semi-Automatic or Constantly Variable Transmission (CVT), or even a clutchless type (Tiptronic, etc). Confused?

Manual Transmission
The manual gearbox has been around almost as long as the car itself. In the early days they were 'crashboxes' and you had to double de-clutch to get a gear. Nowadays, the changing from one gear to another is very smooth indeed and the clutch is light and responsive. Why change a good thing? Well, with the traffic build-up on the roads it becomes a huge effort to keep dipping the clutch and changing gear just to move a few feet forward. Some vehicle manufacturers have now developed a manual transmission that is as normal but without a clutch pedal. This is a revolutionary idea that does away with the need to keep dipping the clutch. These are called 'Tiptronic' by Porsche and 'Sensonic' by Saab. It uses a conventional clutch assembly and gearbox. The clutch is activated each time a gear is selected by an electronically controlled motor activating the clutch instead of your foot. This then disengages the clutch, the gear is shifted and the clutch engaged once more. It all happens within a second and the system evens allows for the car to come to a stop whilst still in gear. The manual gearbox is virtually maintenance free except for the checking of the oil level occasionally. There should however be no grinding noises coming from under the car. If there are, or you suspect that the oil level hasn't been checked for some time, then take your car to your local Unipart Car Care Centre for a quick check and top up if necessary.

Automatic Transmission
Automatic gearboxes were first introduced back in the early part this century in America and still today the Automatic Transmission is predominant there with very few Americans actually knowing how to drive 'Stickshift'. Autoboxes are very easy and pleasurable to drive, especially in built-up areas and towns, where the traffic is constantly stopping and starting. The only thing you have to do after engaging a gear is press the accelerator to go and press the brake to stop. Nothing could be easier! The Automatic Gearbox relies on hydraulic fluid pressure to shift the gears up and down. This fluid needs to be checked regularly to ensure that the level is correct and that the fluid is in good condition. Occasionally, the fluid will need replacing along with any filter fitted inside the gearbox. This is a job best left to your local garage.

Semi-Automatic Transmission
These types of transmission come in various forms. One of them is the 'Pre-selector' Transmission that the older drivers will probably remember being fitted to the Lanchester cars of the forties. These had a fluid flywheel that was engaged by dipping the clutch very swiftly. From then on it was like driving a normal automatic car. Citroen developed one in the 1970's for the GS range. It was roughly the same as driving an automatic car other than you had to select the gears the same as you would with a manual car but without the clutch pedal.

Constantly Variable Transmission (CVT)
This is one that has been around for a while but has only recently been re-introduced. The principal behind this type of transmission is one of being an automatic but with no real gear selection capabilities. Once such type was known as the 'Variomatic' transmission originally developed by DAF. It relied on centrifugal forces throwing out bob-weights within a pulley assembly and the whole lot was driven by drivebelts. It was considered to be over complicated and impractical. But in reality it was a brilliant idea as it enable the car to virtually 'free-wheel' at higher speeds therefore, saving fuel. The CVT is now available in some of the smaller Ford cars. This type of transmission is ideal for town driving and short 'stop-start' trips more so than for motorway journeys.

Clutch
The clutch is an assembly that fits between the engine and the gearbox. It transmits the power of the engine through to the gearbox. The main components of a clutch assembly are the flywheel, the driven/friction plate, the cover/pressure plate and the release bearing. If the friction plate is worn then the car is likely to resist climbing hills and the fuel consumption will increase. This is due to the clutch 'slipping' over the flywheel and pressure plate surfaces. When this happens the friction that is normally between these components is lost and resulting drive to the wheels is reduced. This situation is usually accompanied by an awful smell of burning (the lining material). Replacement of the clutch usually necessitates the removal of the gearbox and this job is best left to your local garage.

Caring for your gearbox: What are the warning signs that my clutch or gearbox may be failing?

Clutch

• If the car requires more revs to accelerate, especially up hills then the clutch may be slipping.
• If there is a burning smell when accelerating especially up hills or when pulling away from stationary.
• If there is a 'graunching' noise coming from the gearbox area when pulling away or when dipping the clutch pedal to change gear. This is usually the release bearing worn due to constant contact with the spinning clutch.
• Never rest your left foot on the clutch pedal when you are not using it as this causes premature failure of the release bearing.

Manual Gearbox

• If there are any strange noises coming from the gearbox, whether it is only when in a certain gear or in all of the gears, it would be advisable to take your car to your local garage for diagnosis of the fault as soon as possible.
• Make sure that the oil levels are regularly checked. If the gearbox runs dry, it could mean an expensive replacement.
• Many gearboxes cannot be rebuilt nowadays, as the main dealers do not list the individual parts needed for rebuild. Instead, the only option is an expensive exchange unit.

Automatic Gearbox

• Check that the fluid levels are regularly checked. This check can be carried out when checking the engine oil level. To check the level, follow the instructions in the vehicle handbook. It may be necessary to check it whilst the transmission is in 'Park' or 'Drive' with the engine running.
• If the fluid is discoloured (brown in appearance) or smells of burning then this can signify that the transmission has been overheated. Replacement of the fluid is then necessary.
• If regularly towing a trailer or caravan, check that your car is fitted with a transmission cooler. If not, it is possible to have an aftermarket kit fitted, as this will prolong the life of the gearbox.

Semi-Automatic or CVT

• Fluid levels must always be checked to ensure that the transmission remains in good condition.
• If drivebelts are fitted, have their condition checked by your local garage.