Auto trans

[4fun Lurker Find all posts View Profile Close 4fun]

Hi everyone just found this page and hoped that someone may be able to shed some light on the way the lock up converter is set up to work on the 2006 120 diesel. I have checked with the local dealer and they don't seem to know. Basically the torque converter lockes up at just above 80 km, thats fine. But the question is why when you take your foot all the way of the accelerator does the convirter let go? effectivly letting the car roll with no enjine breaking. Being use to a manuel this just seems strange. Also when going down steep hills you have to ride the breaks. Is this normal set up. :?:

[Fazza Senior Member Find all posts View Profile Close Fazza]

4fun,

I don,t know about the four speed auto but the five speed with the D4D diesel actually changes down a gear when you touch the brakes when going down hill.
I can't find anything in the handbook about it?

Fazza
07 GXL D4D Auto

[4fun Lurker Find all posts View Profile Close 4fun]

Thanks fazza but the manual does not cover the trany. As it is the first diesel auto I have had it feels strange. Like putting the car in neutral when you want to slow down. the wife has a auto subaru and the converter stays locked when decelerating. feels better.
4fun

[Justo Advanced Member Find all posts View Profile Close Justo]

Will have to take notice but I dont think it would totally let go. I always knock it back into a lower gear if engine braking is needed or just to hold it back that bit down a hill. Can't recall driving an auto that holds you back as much as a manual, so guess it comes down to driver habit.

[Chippy Addicted PP Member Find all posts View Profile Close Chippy]

I am driving the V6 4 spd auto - so the diesel setup may be totally different.

I find the engine braking OK - but then I have been driving automatic Commodores for the last 20 years. Long downhill slopes it does run on more - but then it's also a lot heavier - so I tend to knock it back a gear and the engine braking returns to being OK.

It is an auto - so it's never going to match a manual for that direct (read: not fluid) link between engine and wheels. I just wonder how much of the 'feel' is from just not being used to the slop of a liquid transmission ?

Only a theory

Cheers
Chippy

[Squeaky Junior Member Find all posts View Profile Close Squeaky]

4fun,

I don,t know about the four speed auto but the five speed with the D4D diesel actually changes down a gear when you touch the brakes when going down hill.
I can't find anything in the handbook about it?

Fazza
07 GXL D4D Auto

I have the petrol auto and have noticed the automatic downshift as I touch the brake. Only at speeds under around 30klms. At first I thought it was the brakes grabbing but then I noticed the tacho jump.

[Drew Advanced Member Find all posts View Profile Close Drew]

G'day 4fun and welcome,

The AT750 'box in the V6 prado (and I think it's in the D4-D), does as far as I can tell, unlock when decelerating. But as soon as you lightly touch the brakes, it torques back up and even kicks down a cog in some situations, depending on the attitude sensor data. Yes, the 120 has an attitude sensor and it knows when it's going down hill.

I have a long downhill on my trip home and it's just made for the 120 and the 750 'box, at the top I just lightly apply the brakes as it starts to get away, it kicks back to 4th and holds the 80km/h speed limit all the way to the bottom.

There are situations on steeper sections with lower speeds where I choose to knock the gearbox down manually, the 750 'box is great for this. I live up a 2,500' mountain - any questions about hills and the 120 I should be able to answer. :-)

Hope this helps,

Drew.

[Squeaky Junior Member Find all posts View Profile Close Squeaky]

G'day 4fun and welcome,

The AT750 'box in the V6 prado (and I think it's in the D4-D), does as far as I can tell, unlock when decelerating. But as soon as you lightly touch the brakes, it torques back up and even kicks down a cog in some situations, depending on the attitude sensor data. Yes, the 120 has an attitude sensor and it knows when it's going down hill.

Hope this helps,

Drew.

Thanks Drew, good info and feedback.

[4fun Lurker Find all posts View Profile Close 4fun]

Thanks everyone
Iwill have to try it today when I go out to see if it behaves as Drew said, and thanks drew sounds like you know the Prado well.
Will let you know.
Cheers
4Fun

[Drew Advanced Member Find all posts View Profile Close Drew]

Ah. I had a closer look at this the other day.

When you lift your foot all the way off the accelerator, the tacho drops back close to idle, but about a second later it rises back up. You can't hear or feel anything, it seems to return to a bit less than the revs you would have been doing in overdrive with the gas on.

I guess this is to assist with a bit of engine braking as you would be used to in a manual or an older auto instead of coasting in "angel gear".

Hope this clears things up,

Drew.

[4fun Lurker Find all posts View Profile Close 4fun]

Thanks again Drew
Yes mine drops back as you say but it does not pick up again. Even at 90 kmph it sits on Idle as I slow down. Maybe off to the dealer and have it checked. I also checked when driving mine and you touch the brake slightly it remains in top gear but the lock up convirter dis-engages. so maybe they are set up a little different than the new one.
Thanks again
4fun

[lawrance Senior Member Find all posts View Profile Close lawrance]

My ZF auto gearbox (made in Germany) on my 5 series BMW does the same thing, i.e. when coasting, it unlocks the torque converter and lets the engine speed drop. It doesn't drop to idle but hovers above the 1000 rpm mark or so.

When I step on the accelerator, the auto allows the revs to match the gearbox and locks the torque converter again.