TECH ADVISER’S CHOICE
CHOOSING THE RIGHT GEARBOX
Your article on CVT transmissions addressed all the tech details but I think some readers would like to know which gearbox would be best suited for their particular needs.
CVT is a brilliant design and if the belt was guaranteed to last as long as the rest of the transmission, it would be a great transmission. However, overheating is a big problem and overloading of vehicles will dramatically shorten the life of the CVT belt. Towing should be avoided as this would also cause an increase in heat. Remember, if the belt breaks, you are left with zero drive to the wheels. If you want to tow a caravan or a heavy trailer, look for a car with a torque converter trans‐ mission as this is best suited for heavy loads and towing. This is a proven, trusty design, tested for many years and would be my first choice, irrespective of the application.
DSG boxes on the other hand provide instant gear changes for the sporty driver but can be problematic if the driver is not aware of all the dos and don’ts related to it. For example, do not use the acceler‐ ator to hold the car on an incline, do not let it creep forward under idling as it will chew the clutch plate, do not launch the car improperly, and avoid putting the car into neutral at a traffic light.
Proper maintenance and the correct type of oil is a must to prevent premature failures and this applies to all auto trans‐ missions. Repairing an auto transmission is an expensive exercise. (Also refer to the April 2018 issue for more info on the different auto transmissions.)
JOHAN TERBLANCHE Franschhoek
As the article noted, CVT transmissions are intended as cost-effective, compact and efficient alternatives to traditional torque converter automatics, best suited to small- and mediumsized vehicles with engines developing up to 350 to 400 N.m. The typical towing requirement for this category of vehicles would be for a light trailer or caravan. A check on some of the most popular models revealed the rated towing capacities for the CVT versions to be no differ‐ ent to the MT versions at 750 kg unbraked (legal limit) and 1 000 to 1 500 kg braked. The manufacturers concerned are clearly confident their CVTS are up to the task and rate them accordingly.
Some research on CVT failures revealed no mention of belt breakages, merely some oil pump failures and wear of the pulley and the sides of the belt elements; typically caused by oil not being changed when specified. It would seem belt failures are extremely rare which is not surprising as despite being called “belts”, they are of all-steel construction and work in compression, not tension.
The aspect of the CVT probably most vulnerable to abuse – or misuse – is not the transmission but rather the clutch; the same issue which affects DSGS and MTS. In the case of MT, a sensitive driver can limit slipping of the clutch during a heavy load or uphill pull away and when parking or manoeuvring slowly. On a DSG or CVT, the clutch is electron‐ ically controlled with no direct control by the driver. As you correctly note, the driver’s throttle control will, however, significantly influence how much clutch slip will occur during pull away and low-speed manoeuvring.
Least sensitive to any abuse is the hydraulic torque converter. Usually paired with a conven‐ tional epicyclic (planetary) gearset automatic transmission – to the extent that we often refer to them as a torque converter AT – they have a reputation for being almost indestructible. They are now being fitted to several CVTS, while in the US, Honda builds an eight-speed DCT with a torque converter; the torque converter hand‐ ling pull away and low-speed manoeuvres be‐ fore locking up, while the two clutches handle gearshifts only. In conclusion, you’re quite right in favouring a torque converter AT for heavy towing with a powerful engine; however, for lighter towing, it seems many of the CVTS currently on the market are up to the job.