Doctor Diesel

Auto transmission quandary

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With my local Mazda franchise gone, and the excellent CX-5 that we have corresponded about previously about to enter its sixth year, I have been looking around at alternatives. Two at the top of my list are the Hyundai Tucson and the Kia Sportage. Both with the 1.7 diesel engine and twin-clutch automatic transmission. Also, recently I have been reading and watching technical and test videos on an Australian website featuring a chap called John Cadogan, who has not only been informing and warning the Australian motorist, but also saving them thousands of dollars on new cars and entertaining them at the same time.

 

A point he makes in one of his videos concerns one of my choices above, namely twin-clutch automatic transmissions. He maintains that if your motoring regularly involves heavy traffic with lots of slow creeping along, especially if towing, a twin-clutch transmission could wear prematurely and you should not treat or even think of a twin-clutch transmission as being anything like a conventional automatic transmission, with a torque converter, because apparently it isnít. Also, pick up from standstill isnít as smooth as a conventional automatic. That appears to be one of the trade-offs for snappy changes when getting a move on. Have you had any experience with twin-clutch automatics? The address of this Australian web site is: autoexpert.com.au. I must warn you that he is definitely not star struck by German cars, and I think he has upset quite a lot of Australian owners of them. The presentation is typically Australian, ìTell it like it is mate and no bull.î

 

I’ll be interested in your thoughts and opinions though.

 

Mike Arnold, Barnstaple

 

Hello Michael,

 

Good to hear from you. Sad that you are having to desert Mazda, but I do understand. Twin-clutch transmissions? I ran an Audi A3 Sportback 2.0 TDI DSG back in 2006 until 2008. In those days, hill start assist was optional, and I was tempted by a car in UK stock without it, as opposed to the factory order that I was planning, with hill start assist and a few other options. As I discovered, there is a sort of anti-run-back lock with DSG, which is effectively controlled slippage of the clutches, but the A3 did generally run back about nine inches, and it was a pig to park in a tight spot, particularly on a hill. I have driven DSGs since, with hill start assist, and still experienced much the same shortcomings ñ such as when parallel parking at the roadside on a gradient, between two other cars, with not a lot of space to spare ñ and read elsewhere of others suffering the same experience, and it’s all down to the absence of a torque converter, with its traditional ìcreepî.

 

Now we know that torque converter transmissions (as in a CX-5) supposedly waste energy, but that wastage has been very much reduced, with transmission lock-up when settled in upper gears, and with more ratios in today’s automatics, there is much less slurring and churning in the torque converter. Consequently, the penalties of lower fuel consumption are generally much less significant. I would think very hard before abandoning torque converter transmission in favour of DCT.

 

The best experiences I have had with DSG were in lower power Volkswagen Group cars with the 7-speed dry clutch DSG variant, which works very well when it is working, but is prone to failure. For example, my friend Jim who lives in Somerset, whose Golf Estate 1.2TSI DSG gave him two crises ñ once with complete DSG failure, resulting in total replacement, and then failure of the selector lever electrics. The former problem was undoubtedly related to the synthetic oil problems that a number of those 7-speed DSGs suffered. With my own A3 Sportback, I also felt that performance in slow-moving traffic was flawed, and the power delivery was snatchy in comparison to other cars.

 

The principle of DSG/Twin-clutch transmission is that the unit “knows” what next gear is required, and selects it in advance, so making for very swift changes. But in traffic it of course cannot know which next gear is appropriate, as it doesn’t know if you’re accelerating, or lifting off the accelerator, and there’s no torque converter to cushion sudden changes of transmitted torque in the transmission. I don’t have enough experience of Kia/Hyundai DCTs to know whether they are any better than DSG, or Ford’s PowerShift, and the many others now available. I am not sure how they phrase their handbook instructions, but Kia/Hyundai DCTs are required to be placed in “N” whenever you are stopped, unlike torque converter transmissions, and this is probably to reduce clutch wear in their dry clutch unit, which is the type that seems to suffer most problems. Hill Assist Control operates when you are in ìNî, but the requirement to slip into neutral frequently is a serious negative. Supposedly the “best” DCT is the latest 7-speed Volkswagen Group DSG, which replaces the older 6-speed wet-clutch unit, and is further refined. Reports of it are good.

 

However, I see that you can have a Sportage or Tucson with the 2.0-litre CRDi engine and six-speed torque converter automatic transmission. It’s not as economical as the DCT, and the 1.7 CRDi unit is a pokey engine for its capacity. But in an SUV with over a tonne and a half to pull, 2.0-litres and more torque makes more sense to me than 1.7-litres and less torque. Within the Sportage and Tucson ranges there are a rather confusing number of power variations with the 1.7-litre CRDi and 2.0 CRDi (enough to confuse me, anyway!), but I would see if you can get test drives of the two transmissions and make decisions based on that. You’re very well placed with the long Hyundai and Kia warranties, of course, but that doesn’t mean that you would be happy taking a car back for transmission problems or shortcomings.

 

I think you will feel that I am very much in line in my thinking with Mr Cadoganî and I have avoided mentioning any other alternatives at this stage!

 

Doc Diesel

One Response

  1. My 2005 VW Golf Plus with a 2 litre PD engine DSG lasted till 150,000 miles before Gearbox problem,cannot remember the Fault code,it was stated as Mechanical Fault.The gearbox would go into neutral when warm at a slow speed.This box did not like crawling either.It did have regular oil changes from the box stated every 40,000 miles.I now have a new Vitara with a similar Gearbox called TCSS,I will find out how long this one will last.

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