Weird ZF6 Transmission Issue

[dmbabu]

Hello! Newbie here.

I have a weird transmission issue on my 2012 X5 35d.

When in Drive, when coming from a complete stop (and especially going up a gradient) the transmission does not engage immediately. I have to feather it severally before it gets going. Then suddenly it kicks in and the car lurches forward and we are fine.

Also the car sometimes feels lazy to accelerate (especially when overtaking) but when it catches on it moves just fine.

I don't know if the two issues are related but there are no codes related to the DDE or Drive train.

Never changed my tranny fluid (at 87K miles now)

Could my tranny be slipping? What are the common symptoms of a slipping tranny? Can this be cured by a fluid change and adaptation reset or is it symptomatic of a larger issue? Anyone else ever had this?

[Daytonawim]

Changing The fluid is nog a bad idee.

The lag that you mention is something manny of us feel.

You could try this;

1. Please make sure the ignition is Turned Off

2. Press the Gas Pedal to Full Throttle (while ignition is off).

3. Turn on the Ignition to the 3rd position for 30 seconds (Do Not Crank the Vehicle) (Do Not let go of the Throttle)

4. After 30 seconds are over, Turn Ignition Off and Remove Key (Do Not let go of the Throttle).

5. After Key is Removed, let go of the Throttle and wait 30 seconds.

6. After 30 Seconds, the Car can now be Started normally.

[dmbabu]

I have tried this as well. Severally. Some improvement but only for a short while.

[Daytonawim]

Thats also a thing, I was at ZF for my oil change, and asked if they now about this, they have no idee about that problem.

[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.

[Daytonawim]

That last part of “ auto hold” is incorrect, the “auto hold” function uses the ABS system the keep the car put. When you hit the gas pedaal is releases the brake. When you set the gear to “P” (park) with auto hold on, The parking brake Will be activated automaticly,

You manual have to release the parking brake using the parking brake button.

But i did try the “ auto hold” and it looks like the lag is far less then.

[Daytonawim]

Did some testing today, driving from a absoluut stand still gives no slack from the gearboxwhen driving a way.

Driving along after breaking to near still, gives Some slack in the gearbox.
This time i had a look at the gear display ( i have Xhp so i see the gears ) what happens is that the gearbox Goes Back in gears, but a near stil it’s in 2e of 3e gear, when putting in The gaspedal, the gearbix Goes back to 1e or 2e gear, that gives Some slack in drive.

[robnitro]

Most likely fluid, a friend with a 6hp19 described that down shift lag on his 5 series.
He changed it with mercon SP which is what Ford uses in the zf transmissions and it was great.
But look into the seals too, if you're handy or have a good mechanic.