• The CVT gearbox looks simple in its design but the complexity is in the way it varies the input speed to the output speed.
• The gearbox uses a drive belt or chain to transmit motion between 2 conical pulleys
Automotive manufacturers are competing round the clock to ensure that the assembly lines produce cars that are pocket friendly to the consumers yet very reliable at the same time. One of the most common ways of ensuring a pocket-friendly car is by producing a friendly car at the fuel pump especially for the countries that are yet to embrace auto electric technology.
In short, when a new invention hits the market successfully, within a very short period all the automotive industry must acquire the same or else it risks losing its clientele to the company with the newest pocket-friendly technology.
The introduction of continuously variable transmission(CVT) in smaller cars is a good example of how technology spreads across the board like wildfires. When compared to its predecessor "automatic transmission(A/T), the CVT gearbox is:
- Smaller in size compared to A/T hence less weight
- More smooth and seamless on shifting gear
- More economical on fuel
- Fewer components thus easy to repair
All the above facts complement each other and make it the main reason for most cars to shift from the conventional A/T to CVT gearbox, however, when not taken good care the system is so fragile. Serious damages may occur rendering the gearbox nonfunctional. Getting a new CVT gearbox for some car models is not easy but if you ate lucky to lay your hands on one the price tag is usually not friendly. For this reason, we thought we should talk about its maintenance
HOW IT WORKS
The CVT gearbox looks simple in its design but the complexity is in the way it varies the input speed to the output speed.
Well, we keep it simple, so we shall not dwell so much on the technical aspect. The gearbox uses a drive belt or chain to transmit motion between 2 conical pulleys that vary diameters, when one increases, the other one reduces. It's from this effect that the gearbox gets its name ( continuously variable transmission).
The friction between the chain and the conical pulleys must be very high at all times for the motion to take place.
Talking of friction in a system where oil is key sounds like talking about a white elephant but yes this is the truth. The chain driving the pulleys does not come with any grooves because at one point the pulley is too small and at another point, the pulley is too big depending on your engine speed and load, so having grooves on the pulleys and the chain will not allow the conical pulleys to vary the shape, so yes the only other way to ensure grip is by ensuring that the pulleys and the chain have grip/friction.
Amazingly, the CVT fluid is the one that works the magic of lubricating and providing friction at the same time. It has special additives for grip. The most unfortunate part is that these special additives are not a lifetime. As the CVT gearbox works, the additives in the oil get depleted and at some point, they must be replenished. There is only one way of doing this. CVT oil change. Knowing when to change your CVT oil is very important because it can save you a lot.
Every car manufacturer has different recommendations on what interval the oil should be changed, some vary from as low as 40000 km to 80000km. Most people drive their cars until the gearbox starts developing issues before realising that the CVT oil has never been replaced. For us, at boosted auto, we have a rule of thumb that guides us on this issue. Unless the car is new, if you don't know when the CVT oil was last changed, you better change it and have your records up to date.
CVT OIL CHANGE
As discussed above, every dealer has different change intervals, so is the CVT fluid itself. As much as we agree that there are universal CVT oils on the market, having the recommended CVT for a specific car gives good results. Some manufacturers i.e Subaru have specific CVT oil for their none turbo cars that won't work for turbo cars even though both are Subarus.
Most CVT gearboxes do not have a dipstick.
This was made on purpose because most car owners were fond of using the colour change on the dipstick to determine when the oil change should be conducted. The CVT oil does not easily change the colour even when it has surpassed its interval unless something is wrong in the gearbox or if it was mixed with the wrong oil choice on a previous oil change.
In the past, we have seen unexperienced technicians using ATF to service a CVT gearbox. The consequences are not instant but trust you me this is inviting a death trap to the CVT gearbox. Under normal circumstances when draining out the CVT fluid not all of it comes out. About 20 per cent of the fluid is left in the torque converter. The 20% mixes with the 80 ATF and somehow works in disguise but not for so long before everything starts giving up inside the gearbox.
The bearings and the chain are the most casualties because the lubricating and grip effect in the ATF is not the same as the one in the CVT fluid. The process of CVT gearbox service should only be left with qualified technicians. Special tools and equipment plus experience are highly employed. For instance too much or too little fluid would still cause havoc in the transmission.
Feel free to ask any automotive related question or suggest to us any topic you feel we should tackle in the comments section.
The writer is the owner of Boosted Auto car repair shop