Advice on using automatic gearboxes.

[colbourne]

I have never owned an automatic car before in 25 years of driving so do not really know what the rules are about using and abusing these transmissions.

Can someone please advise what is acceptable behaviour for the following. I have a BA XR8 with the auto transmission.

1) Is it OK to freewheel in Neutral on long gentle down slopes. It appears to save quite a bit of petrol and would reduce engine wear I presume.

2) Is it damaging to shift from Neutral to drive with some throttle to get a better launch.

3) Is holding the foot on the brake and revving before launch going to cause problems. It seems like this is going to put alot of heat into the transmission but I read that this is the best launch technique.

4) How does the lock up work that is meant to prevent transmission losses on the BA auto. Does it work whilst still accellerating ?

5) It states that using the Performance option is better for the gearbox in preventing heat build up. Why ?

6) Is the manual option for the auto the best to use when driving hard ?

[GOLDIE]

This may help you.

1 leave it in drive as it will free wheel slightly in top gear down hill.

2 yes it will damage auto and drive train.

3 only use this at drags as it will build up heat and also stress the auto.

4 usaully not as the auto would kick down.

5 not sure if this is true.

6 I use either depending on where.

Ian

[Turbo6man]

1. NO, it is dangerous and bad driving practice. Answer goes for whether you are driving a manual or auto.

2. YES, it is somewhat like doing a flat change in a manual.

3. If you do this continuously you will certainly shorten the lifespan of your transmission. It will cut maybe a quarter of a second off your accelleration times if you are dragging. Once in a while won't do much harm but this also depends on how you treat the engine/trans generally. If you flog the thing all the time this will just be adding another nail in the coffin.

4. The lock up is to prevent slippage of the torque converter which is like a clutch in a manual car. Torque converters usually slip by up to 15% in normal driving and much more under hard accelleration/heavy load. Once you have reached a certain speed and with low throttle the ECU locks up your torque converter and will release it if a certain degree of throtte/load is applied. It works in both top and overdrive (3rd and 4th).

5. Actually I'd have thought it would be the other way around - the manual for my EF stated that when towing it is best to use "economy" mode. This is because the torque converter is programmed to lock up more in economy mode and therefore stops slip of the torque converter and therefore reduces heat.

6. Personal preference but generally yes, as it gives the driver more control over the balance of the car. You just need to "learn" the delay in the auto's changes in order to maximise your driving control and pleasure.

[Geeseman]

Does the slippage of the torque converter cause a loss in power in comparison with a manual car?

[XR6TK1W1]

Yes it does, slightly. But since this allows revs to be higher it allows slightly more boost from the turbo almost negating this. Hence the auto works very well with the XR6T.

Edited 06/08/04 01:44 AM by XR6TK1W1

[Turbo6man]

  Geeseman said:

Does the slippage of the torque converter cause a loss in power in comparison with a manual car?

No, a torque converter is actually a torque multiplier as well as acting like a clutch - it's slippage allows higher engine revs at any given road speed according to load. At standstill and max throttle it can double the torque applied to the transmission input shaft. This is why autos can run taller final drives and taller gears and still match the accelleration of a manual. Well, mostly. However the heat produced and the inherent inefficiency of the oil medium in producing postive drive means there are some losses.

Most of the loss or lower power output of the auto cars compared to the manuals is because of the heavier transmission components (higher inertia and higher friction) and also the greater number of "interruptions" to the torque flow ie bands, clutches etc. Every connection in the driveline causes heat and therefore loss of power output.

[CHIPS]

  Turbo6man said:

  Geeseman said:

Does the slippage of the torque converter cause a loss in power in comparison with a manual car?

No, a torque converter is actually a torque multiplier as well as acting like a clutch - it's slippage allows higher engine revs at any given road speed according to load. At standstill and max throttle it can double the torque applied to the transmission input shaft. This is why autos can run taller final drives and taller gears and still match the accelleration of a manual. Well, mostly. However the heat produced and the inherent inefficiency of the oil medium in producing postive drive means there are some losses.

Most of the loss or lower power output of the auto cars compared to the manuals is because of the heavier transmission components (higher inertia and higher friction) and also the greater number of "interruptions" to the torque flow ie bands, clutches etc. Every connection in the driveline causes heat and therefore loss of power output.

Spot on Geoff, well written.

[ktford]

  colbourne said:

5) It states that using the Performance option is better for the gearbox in preventing heat build up. Why ?

Yes because it dictates that you'll rarely get into 4th & therefore spend more time above the convertor "lock-up" speed where the transmisson produces less heat.

Scotty

[colbourne]

What is the best way to get the convertor to lock up. In the manual mode can you control this in any way ?

How can you tell when it has locked up ?

[Cro]

I got NFI about what the torque converter does, and what it is...

But judging from the previous post I assume it locks when your revs go under a certain amount.

I.e. your accellerating to 100km/h then you cruise to 100km/h and your revs go down from 4000rpm to 2000rpm..