Z4 automatic vs. stick

Probably because you've already got 'clutches' in a planetary box which can do the same thing. Didn't the Model T Ford use this principle? Later pre-select boxes of course used a fluid flywheel for starting from rest.

Then why do you *have* to have a torque converter? Oh dear, I'll never understand this...

It has several functions. First it acts as a 'clutch' when starting from rest. Next it acts rather like a continuously variable gearbox by allowing the engine speed to exceed its output speed by up to around 2000 rpm and converting most of that speed into extra torque at lower output RPM. Not all though, as it gets hot in doing so. ;-) It also - and crucial for most autos - cushions the actual gearchange.

When autos had two or three ratios, the torque multiplying feature was crucial to reasonable performance - albeit at the expense of economy. Boxes now have up to what? 8 ratios, so this part isn't much needed. So many just use it for starting off and each gearchange, locking it out of action via an extra clutch for most of the time.

A fluid flywheel is not the same as a torque converter. A TC will direct oil flow onto a fixed stator that in turn directs oil flow to a turbine attached to the gearbox input. whereas a FF is simply a spinning container of oil that inertia eventually makes the outside tank oil viscosity turn the vanes of a "spinner" connected to the output to the gearbox. David Brown tractors used to have this arrangement and a similar arrangement although not fluid was the magnetic flux flywheel (clutch less) setup designed jointly by Jeager and Smiths and fitted to the once famous Hillman Minx and I think Simca or Renault cars in France.

Here endeth the last lesson or rather useless information.

Sir Hugh of Bognor

The difference between men and boys is the price of their toys. Intelligence is not knowing the answer but knowing where and how to find it!

Hugh Gundersen snipped-for-privacy@h-gee.co.uk Bognor Regis, W.Sussex, England, UK

Unlike a clutch, it is not possible for a torque converter to completely disengage so there would always be some torque present during shifts which would wear out the synchros in very short order. That's also the reason that a standard transmission will outlast an automatic by a factor of two or three. If you want to keep your car for more than 300k miles I would not recommend an automatic.

I've always had a pretty good grasp of the mechanics of it all, including how the TC works and the subtleties of what it does.

I was kind of thinking that torque multiplication rather than the 'disengaging' effect of low torque transmission at low RPM was the underlying reason they were first used, and I suppose there was then no real reason to change things later.

That's completely the opposite of my quandary!

Which goes against the findings of most large organisations who now specify autos even for things like light vans. The beauty of an auto is it is virtually driver proof. And remember you don't get a synchro transmission without a clutch, so the two should be considered together when assessing life. Not many will get anything like 300k miles out of a clutch.

I agree completely with Dave that the most prominent virtue of the automatic transmission is that it is much more 'foolproof' than the manual transmission and if your situation requires it by all means buy an automatic. That's why commercial operators do it - many of their drivers have no respect for the hardware. On the other point, if a clutch goes out it costs you $150 and a Saturday spent under the car whereas band clutch failure in an auto will cost you about 20 times that amount and will often result in scrapping the vehicle. Automatic transmissions have their place - it's just not in any of my cars.

You're taking a very simple example here. Some clutches these days aren't simple and aren't cheap. The flywheel may also need replacing.

Well it's quite possible to DIY auto box repairs if you take a simple one as you have with a clutch. Nor are the parts that expensive. I've done several. Not a modern electronically controlled 5+ speed, though. Yet. ;-)

The bushing/thrust washer that holds the planetary away from the sun/planetary holder.

FloydR

Poor design or materials, then. Most autos go to their grave without suffering that sort of failure.

"Dave Plowman (News)" wrote

Since almost all GM autos from that era die with that failure, your statement that "most" live is obviously incorrect. I agree that it's poor design: a ball bearing carrier (rather than the cheaper roller bearing and thrust washer) would last much longer. Doesn't change the facts, however.

FloydR

But I'm speaking from a UK perspective. The GM autos from that era used here tended to be the larger ones fitted to Jaguar and Rolls Royce.

Facts depend on where they're gathered from.

"Dave Plowman (News)" wrote

When did we start speaking from a UK perspective? (I'm not going to bother to look, as I no longer care.) This is a global group, not UK specific, so "facts" should be world-wide, not cherry picked from one country.

Later.

FloydR

Indeed. The point I perhaps was trying to make more honestly after you started talking about 'US GMC autos'. ;-)

No. It's a US-perspective (or even LA-perspective) NG...

DAS

For direct contact replace nospam with schmetterling

Since it *is* a US originated group I try to make it plain where I hail from.

Wish it were the case with some others writing to car groups with 'uk' in the title...

What makes it a "US Originated group"?