Regular AT vs DCT: Should you hold it in D or in N while in traffic?

Hans/Jun 24, 2020 10:46 AM

When you are stuck in a traffic jam, should you leave your automatic transmission car in Drive and hold it with the brakes, or shift to Neutral and engage the parking brake/hand brake?

Depending on who you ask, you will get a different answers.

Not very long ago, it was said that you should leave your car in Drive, and that it’s not recommended to keep shifting between Drive and Neutral because doing so sends unnecessary shift shock to the driveline.

ZF 8-speed torque converter used by BMW is one of the best transmissions on the market

But with the kind of traffic that we have these days, is this advice still valid? Plus, today’s automatic transmissions are no longer the same as the ones used 25 years ago.

Automatic transmissions have also become a lot more varied, raising the question of whether are these old views still correct.

Honda Accord now uses a CVT

There are 3 main types of automatic transmissions today – torque converter, continuously variable, and dual-clutch automatics.

Torque converters are the most common ones. Despite being an ‘old tech,’ torque converters are still favoured in many high-end cars because they can handle a lot of torque. Unless stated otherwise, an automatic transmission usually refers to torque converter type ones.

BMW 3 Series' 8-speed torque converter automatic, now shift-by-wire knob

Continuously variable transmissions (CVTs) are perfect for city cars. Favoured by Japanese manufacturers, they are the smoothest for stop-go city driving (Punch CVTs in the Proton Iriz and Persona are exceptions) and are very fuel efficient, but don’t offer a very engaging drive.

Honda HR-V's CVT

Dual-clutch transmissions (DCTs) are preferred by German manufacturers. It offers very fast shift times and offer a very engaging driving experience, but can be jerky in stop-go traffic. It’s also the heaviest and the most complex, but the fuel efficiency and low CO2 emissions offset it.

BMW X1's DCT

So does the advice ‘leave it in Drive when stuck in a traffic jam’ still rings true with CVTs and DCTs? We ask the people who know best – the manufacturers who made the cars.

We asked BMW, Honda, Mercedes-Benz, Proton, and Volkswagen for an answer.

Generally, all manufacturers agree that it is OK to leave the transmission in Drive when you are waiting at a regular waiting time traffic lights (usually no more than 3 minutes), keyword regular – irrespective of what type of automatic transmission types - but there are exceptions.

Honda HR-V's Brake Hold and Electric Parking Brake

Honda recommends that for stops longer than 3 minutes, it is better to shift to Neutral (not applicable to Hybrid models, those can be left in Drive). Proton didn’t give a recommended time limit but recommends the same anyway, advising drivers to shift to Neutral and engage Auto Brake Hold if the car is going to be stationary for long.

Honda adds that its Auto Brake Hold will remain active even after shifting from Drive to Neutral (not applicable to all cars, do try it yourself while holding the brakes).

Honda HR-V

For dual-clutch transmissions, all the German manufacturers say it’s not necessary to shift to Neutral, but there are some driving situations where this is an exception.

BMW, Mercedes-Benz and VW said that it makes no difference whether the driver leaves the transmission in Drive or shift to Neutral.

Volkswagen Golf GTI Mk 7.5's 6-speed DSG

“The system is designed to work in this way. When the Auto Hold is activated or the brake pedal held in a stop position, the clutch is disengaged. No need to shift the Neutral,” explained Volkswagen Passenger Cars Malaysia, adding this applies to all its DSG-equipped cars, irrespective of whether it’s a dry-type or wet-type DCT.

Current VW Tiguan uses a 6-speed DSG (wet)

Meanwhile, BMW Group Malaysia said that it is not true that holding its DCTs in Drive while stationary will add stress to the transmission.

BMW X1 uses a 7-speed DCT

“This is not proven as the torque from the engine would not be transferred to the transmission during this action. Further to this, independent clutch cooling and lubrication would be taking place through the pump motor of the clutch cooling system at this time, preventing any stress to the transmission,” said BMW.

All DCTs used by BMW and MINI models are wet-type ones.

AMG A45 S uses an 8-speed DCT

Mercedes-Benz Malaysia, which only uses wet-type DCTs, echoed the same, explaining that there is very little stress to a DCT’s driveline as the amount of torque generated when the engine is at idle is very minimal.

The A45 no longer uses a floor-mounted shifter, only column-mounted ones

However, it gave one scenario where drivers should shift to Park:

“There will be no added stress to the driveline whether the brakes are applied in heavy traffic or when the vehicle is set to neutral and/or parking pawl is activated. However, when the vehicle is on a steep incline such as a hill for a long duration, it is best to put the vehicle into Park as the clutch friction will increase to keep the vehicle stationary. When the vehicle is stationary in traffic, the pressure to both clutch packs is decreased to the minimum amount required to prevent any excess wear to the clutches but to keep the vehicle stationary and power transmitted to the driveline.”

Proton however, whose locally-assembled X70 now uses a 7-speed wet-type DCT (previous China-made ones had a 6-speed torque converter), chooses to err on the side of caution and suggest that drivers shift to Neutral and make use of the Auto Hold function.

Proton X70 CKD uses a 7-speed DCT

“During prolonged standstill, it is recommended to shift to ‘Neutral’ position for safety (accidental release of the brake pedal) as well as to prolong the lifespan of engine and transmission roll mountings. Furthermore, there is a safety function whereby the engagement of Auto Brake Hold will be automatically shifted to Electric Parking Brake after 10 minutes of standstill. This is to prevent the brake system from overheating,” explained Proton, adding that the same advice (shift to Neutral) also applies to its torque converter (Saga) and CVT-equipped models (Iriz, Persona, Exora).

As for Honda’s i-DCD Sport Hybrid model - City Hybrid, Jazz Hybrid, HR-V Hybrid – all of which run on dry-type 7-speed DCTs, the discussion is irrelevant as the hybrid engine is shut down when the car is stationary anyway.

Front-wheel drive Toyota/Lexus hybrids use E-CVT, which is not a CVT at all, but that's another topic for another day

It should be noted that one should never shift a hybrid car's transmission to Neutral when idling, because doing so will prevent the engine from charging the hybrid battery when charge level is low. If you want to take your foot off the brake pedal, shift to Park, or use Auto Hold (if available).

Maintenance habits for DCTs for longer service life

As explained, DCTs are very complex and proper care is needed to keep it running well.

Mercedes-Benz Malaysia recommends the below:

“Good driving habits are subjective to each individual and the car they are driving itself. For AMG vehicles equipped with DCT such as the A 45 and CLA 45, for example, it is always advisable to ensure the transmission oil is up to operating temperature before spirited driving takes place. Apart from that, the DCT is a very robust transmission. The best piece of advice in regards to preventive maintenance would be to ensure that the DCT is serviced regularly and in-line with the vehicle’s service schedule.

“It is also crucial that the oil and filters for the transmission are changed in a timely manner as the oil provides not only the power transfer for the DCT, but also heat dissipation which should only be done using genuine Mercedes-Benz parts from our authorised dealers to ensure the correct viscosity of oil and genuine filters are used.

“This also allows the workshop to periodically check for any software updates that may be applicable for the transmission as well as other powertrain control units such as the engine control unit software.”

BMW Group Malaysia singles out bad driving behaviour as being bad for a DCT’s service life, “Essentially good driving habits will help prolong every wear & tear components in any vehicle as opposed to spirited or inconsistent driving behaviour which can stress the engine and gearbox over time.”

Honda Malaysia said the same: “Honda recommends to avoid hard acceleration during stop and go driving, especially when driving uphill.

Honda HR-V Hybrid's compact shift-by-wire DCT

Meanwhile Volkswagen warns against modifications: “Follow the recommended service intervals. Chip tuning will affect the performance or longevity of the DSG and drivetrain. Non-standard or wheels and tyres not approved by Volkswagen accessories, could affect the behavior and performance of the DSG.”

How long can the clutches in DCTs last?

While some dry-type DCTs require periodic replacement of clutches (it’s a wear and tear item), wet-type ones doesn’t.

Honda City Hybrid

The only exception is Honda i-DCD, which despite using dry-type clutches, is designed to last the lifetime of the vehicle, which although wasn’t explicitly stated by Honda Malaysia, typically means 15 years/350,000 km. Of course, this is highly dependent on driving and maintenance habits.

The fact that it's a full hybrid also means that the clutch isn't used in standing starts, thus extending its lifespan.

BMW Group Malaysia says all its DCTs are wet-type ones and don’t require replacement. To date, it has not done any clutch pack replacement job but if you have to know, clutch replacement is not possible without a complete DCT component replacement, which will set you back RM 37,150 (as of June 2020) but there's not a single BMW/MINI model in Malaysia that had this job done.

DCT fluid however, requires periodic replacement and this will cost RM 800. “There is not a dedicated time frame for this. The vehicle will alert the driver on the need of this service to take place,” adds BMW.

It’s a similar answer from Mercedes-Benz Malaysia, which said, “The DCT transmission dual clutch packs are designed to last the entire life-cycle of the vehicle. These transmissions are a wet clutch system, differentiating from the dry clutch systems found in conventional transmissions which are designed as a maintenance/serviceable item.

“The benefit of the wet DCT transmission is the reduced wear on the clutch packs due to the constant circulation of oil. This is why, regular changing of transmission fluid in-line with the service schedule is crucial in order to ensure optimum running of the DCT.”

Proton X70

As for the Proton X70’s DCT, Proton says “Under normal driving conditions, the recommended transmission oil change is 90,000km / 54 months whichever comes first. Please use the genuine DCT oil specified for the X70 and do not mix/top up with other brands.” The keyword here is under normal driving conditions.

Proton also adds that the X70’s DCT has been reliably tested to 350,000 km mileage, does not expect an average customer to require clutch pack replacement.

So there you have it. The answer is pretty simple. Stick to the recommended maintenance intervals, drive it with care, and while there are minor differences between Proton’s recommendations for DCT driving habits versus those given by its German peers, we like to think that Proton’s recommendations is something that all users should adopt as its sensible and errs a bit more on the side of caution, which won’t hurt your car anyway.

Also, clutches wear out most when you are accelerating away from standstill, so be gentle when pulling away. 

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