DUAL-MASS MESS
In his youth, the local chemist was called Anton, but long exposure to chemicals had most likely affected his brain so that he developed a speech impediment. Nowadays, he ends every sentence with a hmph sound and, as such, is known as Humphrey (but not to his face).
A year ago, he bought a second-hand Volkswagen Caddy 2,0 TDI. He was very happy with its unique combination of space and car-like qualities. It was his first experience of a turbodiesel engine and his enthusiasm knew no bounds. He told me, “There’s as much torque at low revs as with many 3,0-litre petrol engines hmph. The Caddy will pull my small caravan without even knowing it hmph.”
All went well until last week. Humphrey had been away for the weekend and returned with a very noisy vehicle. The engine sounded very rough, jerked while idling, and there was a tinkling sound inside the bell-housing. Hennie listened with a stethoscope and diagnosed a worn-out dual-mass flywheel.
We contacted a Volkswagen dealership and were told that these units are not repairable and that it will cost R22 000 to t a new one. The warranty was no longer valid because the car was bought second-hand.
I then arranged with my friend Joost, who owns a gearbox-repair centre, to t a new unit for less than half of what VW quoted. I also asked him to tell me more about these newfangled units. It appears that the normal single flywheel is split into two thinner flywheels, with the inner one bolted to the crankshaft and carrying the starter ring-gear. The outer flywheel rides on a bearing mounted on the first flywheel, carries the clutch unit and is able to rotate independently of the inner flywheel. The movement is curbed by circumferential springs that allow only limited movement. These springs dampen the torsional vibration that normally occurs in a crankshaft due to the ring pulses.
Dual-mass flywheels are fitted to many vehicles in the R250 000-plus price range. Their damping action improves gearchange smoothness and reduces transmission stress.
Torsional vibration is at its worst when pulling off and when the driver indulges in lugging. Diesel engines suffer more than petrol engines because their pistons are so much heavier. During lugging, the two flywheels quite vigorously move back and forth with respect to each. The damping springs have such a hard time that they eventually fail.
This means that these units are very sensitive to driving style and, on a number of brands, failures are so common that many workshops replace the dual-mass units with traditional single-flywheel clutch units, provided the owners are prepared to live with the extra vibration.
I tackled Humphrey about this, but he was adamant: “l don’t drive like that hmph. It must have been the previous owner hmph.” We decided to give him the benefit of the doubt.
TRACKER TRACKED
Last week, a visitor to our town ended up with a dead battery on his eight-year-old Mercedes and I sent Japie to fetch the car.
Back at the workshop, Japie put the battery on charge and the next morning, when the battery had a decent charge, Hennie took over to determine why the battery went at. It could have been just a short trip too many, but there may also have been other causes.
Hennie started the car and noticed some error messages. He then remembered that, on some modern cars, a steering-wheel movement should follow a battery replacement. He then moved the steering wheel from full left to full right lock to reset the steering angle sensor and the messages went away.
He revved the engine a few times and noticed that the charging light did not come on, so that the alternator was most likely doing its job. A discharge test showed that the battery was most likely still sound. Finally, he checked for a parasitic current draw by connecting an AVO-meter between the positive battery terminal and its cable. Both the electric clock and the vehicle tracking unit would draw a small current, but the reading he got was about three times higher than expected.
He checked the usual suspects, such as a boot or cubby light that doesn’t go off, by feeling the globe immediately after opening the lid. It would be quite hot if it had been on for a long time. He then decided to look under the bonnet and under the dashboard, and eventually discovered three vehicle-tracking units.
I phoned the car’s owner to nd out which was the current unit and Hennie disconnected the other two. It seems that, every time someone buys an expensive car, new or second-hand, the insurance company demands that a tracker unit be fitted and the installer simply installs another one.