Author |
Topic: torque converter diatribe (Read 966 times) |
|
Mike H
Senior Member
Renault Clio
  
Posts: 2594
|
 |
torque converter diatribe
« on: Sep 18th, 2004, 8:54pm » |
 Quote  Modify
|
Read with some interest about the 'cattle grid' effect, however there may be some confusion about what the torque converter in the auto box actually is - it started off with someone suggesting it may be a centrifugal clutch 'snatching' to produce the symptoms of the fault.
The only centrifugal clutches I've seen were in a lawn mower and a washing machine. According to an old Autocar handbook I've got at home (1948 ), the torque converter was invented by a German, a Dr. Fottinger, in 1905 for variable transmission in steam ships. Then it was adapted for use in Daimler buses by an Englishman before finally appearing in cars.
It has also been known as a 'fluid flywheel', and basically consists of a hollow torus, or hollow annular ring, divided into closed cells by baffles, and split into two equal halves - each a bit like a snail's shell in cross section. One half is connected to the engine flywheel and the other half to the gearbox input shaft. When the engine half rotates it throws oil (automatic transmission fluid) onto the gearbox half, which impinges on the baffles to turn it round.
How it works is the fluid is pushed around by the baffles in the driving half, being thrown out and accelerated by contrifugal force toward the outer edge of the torus. As it turns inward and encounters the baffles of the driven half it loses energy and returns to the innermost side of the torus, and thence into the driving member to be thrown out again. Due to slippage, of which there is always some, the fluid actually circulates around the torus in a spiral fashion. The efficiency is proportional to speed, so at slow speed there is a good deal of slippage, while at high speed the ratio is nearly 1:1 (but never quite).
By itself, therefore, the torque converter provides continuously variable gearing, the actual ratio at any instant being determined by a combination of road speed, load and engine power. You can prove this in use by pressing the gas sharply (not kickdown); the revs rise initially, then the road speed 'catches up' shortly afterward as though the two were connected by a piece of elastic.
It also explains why there are fewer actual gears in the auto box compared with a manual - the variable gearing nature of the converter makes much more than three somewhat superfluous.
It is quite right that one of the things you should make sure of is that the drive is taken up almost as soon as you select Drive or Reverse. Gears are most likely engaged by hydraulic pistons or similar, which is what 'dodgy seals' most likely refers to. It precludes that somewhere in the auto box there is also an engine driven pump to provide the pressure. This pump also keeps the torque converter topped up with fluid as well as circulating it through the oil cooler. The cooler is necessary because in the converter the fluid is transmitting all the engine's output power to the gearbox, and that makes it hot!
On my Exec the oil cooler is a long, thin radiator in front of and below the main rad, half hidden under the bodywork in the engine bay behind the bumper. You can see the front of it by looking through the air gap behind the numberplate. It doesn't come anywhere near the influence of the main rad fans, relying on forward motion only to blow the air through, so make sure it's not blocked with leaves or mud etc.
As for the 'cattle grid' effect, it's only an opinion but my money's still on broken prop shaft bearings or UJ's. These can protest in no uncertain manner when going terminal. Vibration is the least of it. I've seen UJ's where the needle rollers have broken up, actually causing it to seize at a angle. That would make the prop whip up and down like crazy.
|
|
 IP Logged |
Mike H
|
|
|
ron_c
Full Member
Why did I buy this thing????
Posts: 119
|
 |
Re: torque converter diatribe
« Reply #1 on: Sep 18th, 2004, 11:09pm » |
Quote Modify
|
Mike,
Thanks for that. It supports what I learned at my daddy's knee 40 odd years ago when we became proud owners of a Humber Super Snipe Auto and I asked him how it worked. The Humber was lovely but I've never owned an auto since until now and the jury is still out
As for the cattle grid effect, my 2L Scorpio may be showing early signs of this just as it reluctantly engages 4th sometimes and it does display lots of slipping symptoms (which reduces performance and creates havoc with fuel consumption) so I'm not convinced that there isn't some link between apparent cause of poor converter action and symptoms. There is also a Prop shaftish vibration at about 40/50 when the weather is cold so there may well be something in what you say but I haven't the facilities to do any checks myself and have yet to find anyone else that I would trust to do it.
I've had lots of advice about probable causes of my problems but I hate fixing things by trial and error so it will probably fail completely before I find out what the true cause is.
All of this is, of course, more diatribe but it was a pleasure to read your notes.
Ron
|
|
IP Logged |
|
|
|
Mike H
Senior Member
Renault Clio
Posts: 2594
|
|
Re: torque converter diatribe
« Reply #2 on: Sep 20th, 2004, 8:53pm » |
Quote Modify
|
Thanks for that, but I know what you mean. Sounds like what you need is a good man with the right facilities and experience, like one of these self employed mechanic types. I've been fortunate to know one of these guys for some years now and a couple of times he's certainly been worth his weight in gold!
I don't want to guess but two things occur to me straight off - bad bearings will add extra friction, which is like increased load. That could easily do the fuel consumption, especially at speed. Also may be why it keeps dropping out of O/D, because it can't pull the extra loading. Also ATF must become 'worn out' eventually, it doesn't last forever and won't work as well as when it was new by the time it's acquired the viscosity of parafin (or less)...
|
|
IP Logged |
Mike H
|
|
|
|
Home
Help
Search
Members
Login
Reply
Send Topic
Print