Quote:
Originally Posted by Haldex
Hello bunch. Contemplating a new purchase - and having done a test-drive/configuration in July - now I was asked by the dealer to re-do my configuration due to some “technical changes” in the french-market model palette. Now I see that the drivetrain combo that I want is only offered with 7-speed dual-clutch- no more Aisin 8-box. They don’t have it available for test - so I really don’t know what I’m getting myself into.. Has anyone tested the new DCT and can someone share their opinion on it here, specifically how it fares against the good old slushbox? Geartronic was slow alright but it was trouble-free and well suited to the character of these cars/engines offered.. I imagine DCT should provide for quicker shifts and (maybe?..) slightly better fuel economy/performance - but is it as reliable/low maintenance as old-school torque-converters?..
Cheers!  |
All other things being equal there are far more moving and wearing parts in a DCT. The DCT is basically a robotised manual transmission complete with all the synchromesh and selectors that are rammed into the correct ratio by the mechatronics. It has two shafts with a clutch on each so that even ratios are engaged by one clutch and odd ratios engaged by the other. In the background, controlled by the ECU's logic system, the disengaged shaft anticipated the next change to be either up or down and changed the next ratio ready for the clutch to engage its drive. The only exceptions are first and top gear which can only change in one direction.
While the clutches on more powerful cars are wet, oil cooled units that should last a very long time, they must slip to start off smoothly and when creeping along, which should itself be avoided. Eventually they will wear like dry clutches but in general you should expect about five times the life.
However, apart from the complexity and probable long term wear on the gear change mechanism's mechanical complications, the DCT is especially problematic when towing heavy loads. There is no torque multiplying effect for starting off up hill from a torque convertor, so a start is totally reliant on the clutch that engages first, third, fifth and seventh ratios. This is usually a larger clutch than for the other shaft, due to the higher torque of the first ratio starting the car [and trailer] rolling.
The DCT transmissions can be very quick changing but basically the driver should feel no difference when driving to the 8 speed automatic. Except when starting off which inevitably has a more positive, possibly 'grabby' feel.
I have not driven a Volvo DCT and was unaware that they were to be fitted. However I did change from a Volvo XC90 eight speed, which was superb, to an equally superb Kia Sorento diesel with the Hyundai Group Wet8 DCT transmission. Although Kia has a very long and comprehensive warranty, I am not so sure about the very long term durability of DCT transmissions. They do, after all, change ratios in the background and totally undetectable by the passengers/driver, many times more than they actually engage those ratios between engine and wheels by dint of either clutch pack, particularly on challenging roads.