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      10-04-2012, 11:25 AM   #1
baz57
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330d auto box - not the smoothest change?

Having spent a week in a Hyundai genesis coupe 3.8l auto, i think my 330d box ain't the smoothest gear change going. The Hyundai was a 6 speed also. But seamless changes, up and down. Has the competition caught up? Even Toyota taxis seem smoother. The bmw works best at speed of course.
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      10-04-2012, 11:31 AM   #2
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the BMW may seem superficially rougher as it'll probably lock up in each gear more aggressively than the slush boxes on hyundais etc. So it has to unlock each gear before moving on to the next one. My 330i almost felt like a manual box the way it changed gears, i quite liked it!

my 530D however, which had no lock up until 5th, felt quite slushy and smooth.
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      10-04-2012, 11:40 AM   #3
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I'm showing my ignorance, but how do you mean lock up? On rapid acceleration the box is great. Fast smooth change. But when pottering around town, all changes are slightly ponderous, slow and a tiny bit jerky. I drove a jag with an 8 speed box which was super smooth too.
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      10-04-2012, 12:52 PM   #4
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Quote:
Originally Posted by baz57 View Post
I'm showing my ignorance, but how do you mean lock up? On rapid acceleration the box is great. Fast smooth change. But when pottering around town, all changes are slightly ponderous, slow and a tiny bit jerky. I drove a jag with an 8 speed box which was super smooth too.
Traditional auto boxes use a torque converter instead of a clutch. This gives the smooth change, but also will cause revs to rise disproportionate to the speed when you accelerate a bit like a slipping clutch feels, but intentional. When the box is locked, the torque converter doesn't cause that 'slush box' slipping clutch feeling when you accelerate in gear.

Last edited by Falmouthboy; 10-05-2012 at 08:10 AM.
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      10-04-2012, 01:54 PM   #5
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Quote:
Originally Posted by Falmouthboy View Post
Traditional auto boxes use a torque converter instead of a clutch. This gives the smooth change, but also will cause revs to rise disproportionate to the speed when you accelerate a bit like a slopping clutch feels, but intentional. When the box is locked, the torque converter doesn't cause that 'slush box' slipping clutch feeling when you accelerate in gear.
Ah ok, i get it, thanks. I was in abu dhabi in the UAE last week. The Arabs are a little crazy and accelerate fast. All the time! So the auto box would be locked up, giving the smooth change. Eureka!
I will never complain about the standard of UK driving ever again
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      10-04-2012, 02:26 PM   #6
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Fraid you have it the wrong way round bar. I'd expect locking up to make the shifts less smooth not more smooth. I'm thinking locking up may be why yours feels jerky. Boxes that don't lock up and just float the torque converter are generally smoother.

That said, the jag box locks up as often and early as possible too, so if yours feels particularly bad, it may need a service, or it's fluid level checked
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      10-04-2012, 02:54 PM   #7
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If you were to accelerate slowly, the box changes gear slowly. This is my second 330d, this car with 19k on the clock. Both cars boxes act the same but the car was an ex rental so may be worn. Thanks for the info!
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