auto slipping due to too much torque?

[lateshow]

As you might know I have been tuning these cars for ethanol fuel. Well it seems that we are able to get 550Nm from the crank. Or something like that. Just a couple of hours ago we tuned one auto and on 5th it starts to slip around 4000rpm where it reaches the peak torque. It slips about 500rpm. Is this normal? I know that you cant reach torque levels like this normally with gasoline.

[Davezj]

is it actually slipping or is it the torque converter lock up switch in and out.

once the acceleration phase is complete and the car speed stablises the revs nromally drop by about 500rpm when the torque converter locks up and so all the torque accross the troque converter is supplied to the gear box.

could it be something to do with this, i am not convinced but it was just a thought.

[Nick Mann]

That's about 370 lbft in Olde English. I have had that on an auto and the only slippage was as Dave describes - the torque converter doing it's job. It didn't lock up when accelerating hard, but IMO it shouldn't normally.

[Davezj]

i was not sure in any respect as i was of the same opinion that the torque converter lock up only occured when the car was not accelerating any more.

but could you get a lock up due to some kind of fault or over heating and then have the lockup unlock due to the extra torque, or something like that i don't know enough about torque converters and auto gearboxs to make a proper reasoned argument for or against.

as i under stand the operation of the torque converter the 2 or 3 vained/finned surfaces not mechanically connected together rotate within the outer body of the torque converter and it is oil/fluid (not the ATF) that heats up and make a viscous fluid between the vains/fins which effectively binds the separate surfaces togerther.

i would imagine the clutch pack in an auto box could slip .

[John TheAntique]

If it's slipping wouldn't the revs go up?

[lateshow]

On 5th gear when it hits 4000rpm the revs go up 500rpm suddenly. Everything else works normally. And at that point the gearbox should work like a manual. When looking at the "dyno sheet" the actual slippage alway happens at 3000rpm when you flloor it. Im glad I have manual now.

[Colin Wiltshire]

Really sounds like the torque converter, when I had an auto it was forever (what I'd call half changing, eg gear 3.5) that was always around 500 revs difference.

[Davezj]

i was more thinking of a faulty torque converter, early lock up of the torque converter and then it unlock as it should do under higher load. not the standard operation of the converter.
it was just a thought as the 500 rpm change seems quite coincidental.

i would have thought if it was one of the many clutches in tha auto box itself, then once the clutch starts to slip i would have thought it would continue to slip once the tourque increases and not just slip by 500rpm then continue to hold the toruque to the red line as is beening suggested.

well i am assuming that this is what is being suggested as only a 500rpm slip is ever mentioned.

[Nick Mann]

Does anyone know the mechanism for the torque converter to lock? I think it only happens in 4th and 5th. How does the torque converter know which gear it is in? Does the gearbox change the pressure to the torque converter to lock it? Or is the gearbox able to bring a clutch in that locks the shafts from the torque converter together in the box?

[BubbaLeggyVR4]

Hey, some of u know I'm into my hydraulics so heres my take...a torque converter is made of 3 parts essentially
a. Turbine
b. Pump
c. Stator
When the engine is on low load(tickover) less oil is flowing against the stator. The pump is connected to the engine output shaft and the turbine is on the gearbox. Its a directional fluid change which makes it work with the help of the stator. The torque convertor locks up when near equal pressures are attained on the stator, which in turn runs on a one way bearing assembly, forcing the fluid to change direction and thus producing steady torque as the engine and road speeds are matched.
Cant say why it would slip unless the oil is no good or damaged part in torque converter.
Hope this helps someone lol :)

[TAR]

have a look at this, its quite a good explanation without being too technical

http://auto.howstuffworks.com/auto-parts/towing/towing-capacity/information/torque-converter.htm

:happy:

[Nick Mann]

But I understand the basic fundamentals in that article. The bit I am unsure of is how the torque converter locks. That article simply says "To counter this effect, some cars have a torque converter with a*lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency."
That doesn't make it sound like an equal pressure thing so much as a physical clutch.

[Subaru ETA]

It has a physical clutch. From memory (been a while since I have got into auto trans stuff - not really my thing), it uses road speed as its switching point and will only lock up in top gear.

Once the speed is reached it activates a valve which sends pressurized fluid to the clutch causing it to engage. When it needs to disengage the valve releases the fluid

[Davezj]

here is an animation that explains the lock up clutch but not the actual activation device, but i now understand the proper basics of torque converters.
it is a bit corprate american delivery of the naration but worth watching.

http://www.youtube.com/watch?v=hhwYIs6Lu3M

once you have watch the fist animation watch this video from eric the car guy he completely disects a torque converter and show what is going on.

http://www.youtube.com/watch?v=pTfipsejqS0

and if you are interested to see what the inside of an outo box looks like and what things do inside then these 2 videos are worth watching, it is a complete strip down of an auto box, not necessaraly to put back together but just to show what can go wrong and the complexity of them.

Part one
http://www.youtube.com/watch?v=JGbsgpp2YJQ

Part 2
http://www.youtube.com/watch?v=0Qf6O0oAs7U

eric the car guy is great for videos like this and he has loads on youtube, just search for them.

[BubbaLeggyVR4]

Good videos, I even learnt something lol
The auto is good but I still think manual is a safer option, considering what can go wrong

[Babylon6]

Very good those Eric videos