Auto lockup

[kaiser]

Of course I'm right.
I'm always right!

And when I'm not right, I am certainly not left!

[SD1too]

Originally Posted by wutang

you should notice lock up once in fifth gear the revs will then drop again by about 300rpm. if you put your foot down again the revs will rise without an actual gear change as the converter un - locks again.

Originally Posted by kaiser

... the first thing the box does, if you want to accelerate even moderately, is to drop about 400 revs. That is when the box goes out of lock up.

Originally Posted by Parker

.. whilst in 5th once reaching around 65 MPH there is a dip in the revs which is noticeable.

Evening gents,

I've just returned from a couple of days driving on A roads and motorways during which I made a renewed attempt to detect torque converter lock-up. I did notice the reduction in revs described in the above posts, but this seemed to correspond with an upchange from 4th to 5th, as verified by immediately moving the gear selector back to '4' and noting the tachometer reading. I wasn't able to link any reduction in revs irrefutably with torque converter lock-up.

It's worth bearing in mind that at a constant road speed in a high gear (e.g. 5th) the torque converter's impeller speed is relatively low, and so is the turbine speed. A state of equilibrium exists where the inertia of the transmission fluid within the converter contributes greatly to maintaining the steady road speed. It is my understanding that by-passing this fluid coupling with a mechanical connection ("lock-up") is therefore unlikely to result in the dramatic reduction in revs previously suggested. In addition, MG Rover says that the engagement of lock-up is achieved progressively by a gradual change of hydraulic pressure. For all these reasons, I am still unconvinced that we can detect when lock-up is activated or deactivated, particularly if it coincides with an upchange or downchange of gear, which is entirely possible with sophisticated ECU control systems.

Simon

[crofts]

Dammit............that answers the next question I was going to ask.......I think.
Reminds me of the saying 'The angle of dangle is equal to the heat of the meat'........don't know why though !

[kaiser]

Originally Posted by SD1too

Evening gents,

I've just returned from a couple of days driving on A roads and motorways during which I made a renewed attempt to detect torque converter lock-up. I did notice the reduction in revs described in the above posts, but this seemed to correspond with an upchange from 4th to 5th, as verified by immediately moving the gear selector back to '4' and noting the tachometer reading. I wasn't able to link any reduction in revs irrefutably with torque converter lock-up.

It's worth bearing in mind that at a constant road speed in a high gear (e.g. 5th) the torque converter's impeller speed is relatively low, and so is the turbine speed. A state of equilibrium exists where the inertia of the transmission fluid within the converter contributes greatly to maintaining the steady road speed. It is my understanding that by-passing this fluid coupling with a mechanical connection ("lock-up") is therefore unlikely to result in the dramatic reduction in revs previously suggested. In addition, MG Rover says that the engagement of lock-up is achieved progressively by a gradual change of hydraulic pressure. For all these reasons, I am still unconvinced that we can detect when lock-up is activated or deactivated, particularly if it coincides with an upchange or downchange of gear, which is entirely possible with sophisticated ECU control systems.

Simon

It is of course possible that something here does not work as it should.

It could possibly be your box.

[Ford Prefect]

Originally Posted by SD1too

Evening gents,

I've just returned from a couple of days driving on A roads and motorways during which I made a renewed attempt to detect torque converter lock-up. I did notice the reduction in revs described in the above posts, but this seemed to correspond with an upchange from 4th to 5th, as verified by immediately moving the gear selector back to '4' and noting the tachometer reading. I wasn't able to link any reduction in revs irrefutably with torque converter lock-up.

It's worth bearing in mind that at a constant road speed in a high gear (e.g. 5th) the torque converter's impeller speed is relatively low, and so is the turbine speed. A state of equilibrium exists where the inertia of the transmission fluid within the converter contributes greatly to maintaining the steady road speed. It is my understanding that by-passing this fluid coupling with a mechanical connection ("lock-up") is therefore unlikely to result in the dramatic reduction in revs previously suggested. In addition, MG Rover says that the engagement of lock-up is achieved progressively by a gradual change of hydraulic pressure. For all these reasons, I am still unconvinced that we can detect when lock-up is activated or deactivated, particularly if it coincides with an upchange or downchange of gear, which is entirely possible with sophisticated ECU control systems.

Simon

Mine has engaged 5th before it reaches 50! , once it has locked up in 5th the RPM sit at about 2100, you can tell when its locked up by very gently applying a little power then removing it, the revs will rise without a speed increase and then drop if it's not locked up

[kaiser]

The logical way to state this would be to say more or less the follwing

If un-locked, a light press/release on the speeder will result in a increase/decrease in engine revs at constant road speed, showing the slip in the torque convertor.
If locked: a light press/release on the speeder gives no change in the engine revs, thus showing the direct, locked linkage of the box.

And this is exactly how it is. Go and try it yourself.

[SD1too]

Originally Posted by Ford Prefect

Mine has engaged 5th before it reaches 50! , once it has locked up in 5th the RPM sit at about 2100 ...

There's something odd here Stewart. MG Rover data for the 2.5 litre auto with 215/55 R16 tyres is 27.4 mph per 1,000 rpm in 5th gear. This gives a true 57.5 mph at 2,100 rpm. Your speedo, with its 10% error, should be indicating around 64 mph.

Simon

[kaiser]

As far as I remember. Mine does about 130km/h at about 2800 revs.
That would be equal to 47 km/h/1000revs. Or 29mph/1000 revs.
2100 thus would be almost exactly 60mph.

I have timed mine on road markings, and mine shows about 6 to 7% above. 130km/h true (about 140km/h on the clock) is thus safe for 120km/h highways, with a 10% allowance.

[Ford Prefect]

Originally Posted by SD1too

There's something odd here Stewart. MG Rover data for the 2.5 litre auto with 215/55 R16 tyres is 27.4 mph per 1,000 rpm in 5th gear. This gives a true 57.5 mph at 2,100 rpm. Your speedo, with its 10% error, should be indicating around 64 mph.

Simon

Not really, the 10% error is not a fixed definate, thats the maximium margin or erro allowed under the EU directive for such things, and is just a maxiumum, as long as it does not show a lower speed, and is no more than 10% fast then its allowed, so theres no requrement.. but it does read between 62 and 65 when it locks up and RPM do seem to be 2100 ish so yeah you are right! 5th seems to engage at near 40 (only know this as I was counting the gear changes tonight!)

[SD1too]

Originally Posted by Ford Prefect

Not really, the 10% error is not a fixed definate ...

I was referring to practical tests which I have carried out, not regulations. My speedo over-reads by exactly 10% and I believe that this applies to all 75s and ZTs.

Simon