torque converter behaviour

Transmissions, Transfer Boxes, Axles, Drive Shafts
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biggles
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torque converter behaviour

Post by biggles » 21 Sep 2015 10:39

I am not at all experienced with autos. And something that has bugged me for a while is that when you put foot the engine revs jump by 500rpm before it translates into forward acceleration.

Something that I have seen on aussie patrol forum is altering the torque converter when doing a 3.0di to 4.2Td conversion.

So is it normal for the revs to jump up like that. I assume at the very least the torque converter lock up function is not working.
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Re: torque converter behaviour

Post by Peter Connan » 22 Sep 2015 06:47

I am no expert with autos or torque converters either, but would assume that the torque converter lockup would unlock when flooring it.

I was also under the impression that only the 4.8 has a locking converter?
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Re: torque converter behaviour

Post by Herrie » 22 Sep 2015 07:41

I also need auto box information to sort out my son's auto box on his Safari!
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Re: torque converter behaviour

Post by bogeyman » 22 Sep 2015 09:28

A torque converter with auto box does the work of a clutch with a manual box.
At idle , the converter freewheels and thus allows the engine to turn with the gearbox stationary.
When power is applied , engine revs are converted to torque and the gearbox starts turning.
As speed increases , the gearbox will upshift and the converter will accommodate the difference in engine rpm and gearbox input rpm.

If fitted , the lockup function will only engage when a steady speed with steady engine power is applied. I think that the 4.8 tiptronic box will also engage lockup in 4x4 under certain conditions to aid with engine braking.

A converter allows you to apply very high torque to the wheels at very low wheel rpm with more control than with a manual clutch.

The rise in engine rpm you ask about is an exchange of rpm for torque and as the power/load ratio changes , the difference between drive and driven shafts will change. (within limits and including component losses)

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Re: torque converter behaviour

Post by Johannes van die See » 22 Sep 2015 14:17

bogeyman wrote:If fitted , the lockup function will only engage when a steady speed with steady engine power is applied. I think that the 4.8 tiptronic box will also engage lockup in 4x4 under certain conditions to aid with engine braking.
Is this "Lockup Function" an after market fitment or does it come standard with the 4.8 Tiptronic Box?
Im new to Auto 4x4 driving and was wondering about engine braking during a steep descent, what can I expect from my 2008 model 4.8 Tiptronic?
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Re: torque converter behaviour

Post by Peter Connan » 22 Sep 2015 21:00

Johannes, the lockup is standard on the 4.8.

I do not know if it locks up during descents, but in my limited experience with 4.8's you will want to augment engine braking with the big pedal. Fortunately it has discs all round, so you are very unlikely to suffer from fade in these conditions, and they are easy to modulate.
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Re: torque converter behaviour

Post by Bruin Beer » 23 Sep 2015 07:45

Johannes,
This is according to the manual.
Hope this is of some help.
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Re: torque converter behaviour

Post by David » 23 Sep 2015 10:04

Johannes the lockup is standard.

Engine braking when using the tip-tronic is actually quite good once you know how to use it. On steep mountain passes I often put it in manual 3rd or second if I want to keep the speed down. I can't remember the exact speeds but In low and high range it will limit your speed quite effectively with only slight braking with the foot needed on really steep descents in low first.
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Re: torque converter behaviour

Post by biggles » 23 Sep 2015 10:57

So back to my original question:

When I plant my foot is the 500rpm increase before any change in drive is felt normal?

P.S> The 3.0Di auto has lock up above certain speeds.
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Re: torque converter behaviour

Post by David » 23 Sep 2015 12:41

I have the 4.8 which is slightly different but I think it is normal behavior.

I will be cruising @ 2000r/min and when accelerating or against an uphill the torque converter will unlock and revs will jump +-500rpm. Your throttle position definitely plays a role.
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