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Old 18th October 2007, 16:49   #1
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Default Automatic clutches

Hi Team,

My uncle was in the market for a second car, and is seriously considering the Santro Automatic. Until someone tells him that clutches in ATs in India wear out prematurely because of the continuous clutch changes by the Auto in stop go traffic.

He's looking at buying the car in Bangalore, and traffic there is probably the worst it can get, and he asked me whether that is the case. Logically it seems plausible that the clutch would get "used" more in heavy traffic, but I'm unsure as to whether that leads to early clutch failure.

Comments? thoughts? Experiences?

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Old 18th October 2007, 17:15   #2
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Automatic Transmissions couple to the engine's flywheel by means of a Torque Converter. This is a giant doughnut shaped contraption filled with transmission fluid.

Fundamentally it is a hydro-dynamic fluid clutch that transfers rotational energy from the spinning engine flywheel to the gearbox -- your rotating driven load.

When there is a substantial difference between input and output rotational speed, such as when the car is stationary, the TC provides torque multiplication, like what a low gear would provide.

There are at least 3 rotating elements, (sometimes 4):
  1. the impeller (pump) that is rotated by the engine,
  2. the turbine which is spun by the flowing transmission fluid
  3. and at least one stator (often non rotating, but sometimes unidirectional rotating), which directs return fluid flow from the turbine back to the pump.
  • When you place the selector (shift lever) in "D" and hold the car with the brake pedal, the torque converter is in stall mode.
  • When you let go the brake pedal, and in a moving car, press the accelerator, the torque converter is in acceleration mode.
  • When the car is cruising with the turbine spinning 90% as fast as the impeller or faster, the TC is in coupled mode. This is when the lock-up clutch kicks-in and physically mates the turbine to the impeller, letting the fluid cool.
The clutch failure that you allude to, would happen if you hold the brake pedal down with your left foot and excessively rev up the engine with your right foot. The TC body will then be subjected to excessive pressure. This can blow up the aluminum housing like a balloon. It would burst, spraying transmission fluid and bits of metal all over the place.

But rest assured that stop-n-go traffic would not wear out your torque converter unless you have used a very wrong grade of transmission fluid, or you are attempting to tow a load far too heavy for your Hyundai Santro automatic.

Hope this helps.

Cheers...
Ram
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Old 18th October 2007, 18:30   #3
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Quote:
Originally Posted by superavi View Post
My uncle was in the market for a second car, and is seriously considering the Santro Automatic.
You cant get a Santro AT, as the production has stopped (unless you are thinking of getting a used one, or something which is left in the dealer's stock).
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Old 20th October 2007, 17:07   #4
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Thanks Ram. So you're saying the clutch will not be a problem at all and should ideally last longer than the clutch of a manual?

Sukhoi - are you sure about the Auto Santro meeting it's end? Too bad in that case.

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Old 20th October 2007, 17:22   #5
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There are news that Hyundai Pa will be coming with AT.
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Old 21st October 2007, 14:13   #6
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Quote:
Originally Posted by superavi View Post
Sukhoi - are you sure about the Auto Santro meeting it's end? Too bad in that case.
I called a dealer sometime back and he told me about this. He also mentioned that Pa would have AT, so I can wait for it, if I am keen on AT.
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Old 21st October 2007, 16:17   #7
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Ram is saying that one can forget about clutch in an AT: it is an entirely different mechanism!

India is far from the only place in the world to have slow, stop-go city traffic.

An Auto is ideal for these conditions and makes them very easy to handle (or should that be footle? ). It is the manual transmission's clutch that will suffer more, especially if the driver is a little lazy or does not use correct technique.
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Old 22nd October 2007, 17:19   #8
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If you follow proper driving practices (refer the vehicles hand book for the same) you can extend the wear out period
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