A340 auto box & Battery Isolation/Kill switch....

[50RTD]

Hi guys,

What happens to an A340 when all power is cut during operation?

Im fitting a kill switch in-cab and while considering the best possible mounting point for an emergency 'off', it became apparant that there is the potential to accidentally 'kill' the vehicle's power during everyday operation... never something ive had to worry about, as ive only had manual vehicles but question is... Will killing all power to an A340 cause any negative or catastrophic events??

Cheers

-Dan

[George]

Killing engine stops trans's oil pump which is generally bad (for example towing an auto trans car is usually allowed only while in N, low speed&short distance)

The box itself when power is cut will operate solely from its hydraulic system's "opinion" and lever position as per car's manual. However I can't figure out what could happen without oil pressure (engine stopped)

[50RTD]

Cheers for reply George,

The case i was thinking was 'accidentally hitting kill switch at 100kph or more' for example, where in a manual (whilst still in gear), the driveline will keep spinning the engine over with no major worries, acting as a compression brake as such..

What happens in an auto in this situation?? Say kill switch gets flicked in 3rd or overdrive?? Is it the same as a manual i.e, continues to freely turn, with the engines compression eventually slowing the car down??

[George]

Sadly I can't describe this in details, all I know that it will most likely damage the box, or more exaclty its converter.

[RA40Rob]

if engine stops the trans oil pump stops= no hydaulic pressure to hold clutches together properly and no lubrication to bearings/planataries. This may do little damage for a very short time but would not recommend it.

[midnight_purple_GA70]

no power to an a340 defaults it to overdrive...

if it is a cable kickdown style valve body then i dont see electrics doing a thing to the box...
for example when wiring up a "shift box" to engage overdrive you cut all power to the gearbox...

that being said the engine is usually running at the time so not sure how it would react if the motor isnt running...

[50RTD]

Thanks for the replys guys, greatly appreciated.

I guess avoid accidentally hitting the isolator at all costs is a bloody good idea!

[midnight_purple_GA70]

yeah definitely not recommended...

maybe look at shifting it so its not able to be accidently hit?

[50RTD]

Im setting it up so in needs to be flicked upwards (also has a cable connected for actuation from outside the vehicle, as per Cams/Andra regs...)

Ive always believed it needs to be in an easily accessible enough position, so in the event of an acco, it can be easily flicked, although that also means the potential to easily 'accidentally' hit it exists.

That said, ive had the same setup in a semi-competition spec 4wd without any dramas (with arms and legs often flying around the cabin haha), but never worried me as it was a manual...

Thanks for your help again mate!

[1JZ-Rolla]

no power to an a340 defaults it to overdrive...

if it is a cable kickdown style valve body then i dont see electrics doing a thing to the box...
for example when wiring up a "shift box" to engage overdrive you cut all power to the gearbox...

that being said the engine is usually running at the time so not sure how it would react if the motor isnt running...

No power will only default to overdrive if the shifter is in the D (3rd) position. In 2nd position it will default to 3rd from memory, either way, it will always try and go for a higher gear, so no great worry.

Mate what do you mean by "kickdown" style valvebody by the way, and how does it relate to shifting? My understanding is that it only controls line pressure (i.e how much force is apprlied to the bands/clutches), as opposed to the later boxes that used a PWM solenoid to do the same thing based on TPS input from the engine ECU.

Either way, as has been said, engine stopping while the car is in motion will result in no hydraulic pressure in the box, since the internal oil pump stops, so therefore no engine braking, and no lubrication for the remaining box internals that are still turning.

This may or may not do noticeable damage, depending how fast you are going, and how long it takes you to come to a standstill. I had to shut down the motor in an automatic LS1 powered Commodore ute (throttle stuck at 100% and hurtling toward an intersection at great speed), the box still performs faultlessly in a functional check 5000km later, but who knows if there are signs of damage internally on the rotating components.


Cheers
Phil

[Mole]

Even though the internal oil pressure will stop, wont there still be residual oil that will provide at least some protection, for a (very) short period at least?

[LeeRoy]

Correct me if i'm wrong but if you kill the engine even in an auto won't the motor just continue to be turned over by the cars momentum, and as such continue to rotate all of the driveline, including gearbox, torque convertor, and pump? Do remember you'll have fluid in the torque convertor at the moment of shut off, and that would remain (although decreasing?) - but would it remain until the car stops?