Weird ZF6 Transmission Issue

[robnitro]

When at a stop in D, the 6hp trans saves fuel by disengaging the gear, so that there's no torque transmitted through the torque converter.
Letting go of brake should quickly engage 1st.
Try seeing how long it takes to move after releasing brake without hitting the gas.

You can also switch to manual mode and pick 2nd gear to start from and see if the issue persists.
But if you're having lag you might not only have old fluid but the level might be low.
If you can do the bridge seals while getting the fluid change, that's also a possible issue as they get brittle and can leak a bit of pressure.

Also make sure you have auto hold off. This uses the parking brake when stopped and can cause lags.

[dmbabu]

Originally Posted by robnitro

When at a stop in D, the 6hp trans saves fuel by disengaging the gear, so that there's no torque transmitted through the torque converter.
Letting go of brake should quickly engage 1st.
Try seeing how long it takes to move after releasing brake without hitting the gas.

You can also switch to manual mode and pick 2nd gear to start from and see if the issue persists.
But if you're having lag you might not only have old fluid but the level might be low.
If you can do the bridge seals while getting the fluid change, that's also a possible issue as they get brittle and can leak a bit of pressure.

Also make sure you have auto hold off. This uses the parking brake when stopped and can cause lags.

Interesting. I have an F31 with the ZF8 transmission which can disengage (for coasting). Didn't know the ZF6 can also disengage for economy.

[robnitro]

Originally Posted by dmbabu

Interesting. I have an F31 with the ZF8 transmission which can disengage (for coasting). Didn't know the ZF6 can also disengage for economy.

Yep. I was watching the fuel rate in bimmer-tool Android app when stopped in D and saw it go from 8mg/R (milligrams per revolution ) to 7.
Releasing the brake, it went back up to 8.
Another time I flipped over to S and shifted to 2 while stopped, same thing, fueling jumped up. (Can't do the disengaging in 2 as it uses a different clutch than 1)
For comparison, switching to N , the fueling goes down to 5 or so. The disengagement uses more fuel than N because the transmission is still active, it just cuts the torque going through the converter by disengaging clutch A IIRC.

I'm running my own xhp custom tune but I never could find the switch that turns on this ability so I never thought I would have it, but it seems it's part of the basic program.
The only odd thing is that sometimes it won't happen at all and I cannot find a pattern it's linked to, whether it be engine temp or transmission temp.