[jjrichar]

Having a bit of experience with this transmission, here's my take:

1. I know the manual states that it's critical for the temp to be correct for filling. It actually makes very little difference at all. I've done the testing and it's insignificant, especially considering the regime where the issues are occurring in the car. For normal driving, you could drop a litre or two (or overfill by the same amount) and not notice any change. Driving the car very hard would show you a problem though. That being said, checking the fluid level with the fluid feeling just a little warm with your hand on the pan is a good thing to confirm.

2. If the fluid level is low, unless extremely low and it's just sucking air, problems occur normally during hard acceleration due to the fluid flowing to the rear of the pan and the filter intake (right at the bottom of the pan) being uncovered and air being sucked into the pump.

A few questions for the OP.

When driving in manual mode, did you do the gear shifts at exactly the RPM and accel level where they occur when using D? Did you get the same result?

In M, when either 3rd or 4th is engaged and you floor the gas pedal, is there an immediate increase in RPM that is unlike what you would normally expect?

 

[Anticdubai]

I've done the testing and it's insignificant, especially considering the regime where the issues are occurring in the car. For normal driving, you could drop a litre or two (or overfill by the same amount) and not notice any change

Respectfully, I have to disagree.
Yes you are right in normal driving that ''liter-two'' might not affect your daily driving. Or might. At my experience, after workshop replaced aATF, I found that if I make hard turn , gear drops to 4 from 5 - as I always drive in manual mode. Suspecting underfilling, I visited workshop and they checked it in front of me, demonstrating fluid flow out of flling hole. On hot transmission, of course. Unfortunately, at those days I didn't know much about transmission. I clearly understand it now. Low leveel can lead to excessive foaming and premature wearing of srictions.
Also, my own experience - filling at 70c gave me a 1 L low level, comparing to 40C.

 

[Turbotop]

Having a bit of experience with this transmission, here's my take:

1. I know the manual states that it's critical for the temp to be correct for filling. It actually makes very little difference at all. I've done the testing and it's insignificant, especially considering the regime where the issues are occurring in the car. For normal driving, you could drop a litre or two (or overfill by the same amount) and not notice any change. Driving the car very hard would show you a problem though. That being said, checking the fluid level with the fluid feeling just a little warm with your hand on the pan is a good thing to confirm.

2. If the fluid level is low, unless extremely low and it's just sucking air, problems occur normally during hard acceleration due to the fluid flowing to the rear of the pan and the filter intake (right at the bottom of the pan) being uncovered and air being sucked into the pump.

A few questions for the OP.

When driving in manual mode, did you do the gear shifts at exactly the RPM and accel level where they occur when using D? Did you get the same result?

In M, when either 3rd or 4th is engaged and you floor the gas pedal, is there an immediate increase in RPM that is unlike what you would normally expect?

In manual it never happens. I think it has something to do with tor.clutch engagement. I uploaded a video on YouTube for a visualization what happens when.

The problem occurs at 0:06. See the dip in RPM that goes simultaneously with a jerk in acceleration.

Translation:
It drives in third.... then shifts to fourth... and now... it gives a jerk .... what might be the problem?

 

[azadani]

Respectfully, I have to disagree.
Yes you are right in normal driving that ''liter-two'' might not affect your daily driving. Or might. At my experience, after workshop replaced aATF, I found that if I make hard turn , gear drops to 4 from 5 - as I always drive in manual mode. Suspecting underfilling, I visited workshop and they checked it in front of me, demonstrating fluid flow out of flling hole. On hot transmission, of course. Unfortunately, at those days I didn't know much about transmission. I clearly understand it now. Low leveel can lead to excessive foaming and premature wearing of srictions.
Also, my own experience - filling at 70c gave me a 1 L low level, comparing to 40C.

Yes I'm calling incorrect on that statement too, based on seeing the difference just today.

To say that a gearbox that holds 9L can go with 2L less (22%) is just not good advice at all, and could lead to expensive repairs or at best early wear.

OP, you need the correct fluid filled to the correct level. That goes for any fluid filled aspect of any car. You wouldn't run the motor with 22% less oil.

 

[Turbotop]

I got ZF to check my fluid level and test as service on monday. I'll keep you guys up to date if there is any progression.

 

[jjrichar]

Respectfully, I have to disagree.
Yes you are right in normal driving that ''liter-two'' might not affect your daily driving. Or might. At my experience, after workshop replaced aATF, I found that if I make hard turn , gear drops to 4 from 5 - as I always drive in manual mode. Suspecting underfilling, I visited workshop and they checked it in front of me, demonstrating fluid flow out of flling hole. On hot transmission, of course. Unfortunately, at those days I didn't know much about transmission. I clearly understand it now. Low leveel can lead to excessive foaming and premature wearing of srictions.
Also, my own experience - filling at 70c gave me a 1 L low level, comparing to 40C.

That is interesting feedback. The testing I did wasn't underfilling and then driving, but accurately measuring the expansion of the fluid (in a test tube) as the temp rose from 40C to 100C. To be honest it was barely noticeable. Less than 1%. ie Less than 100ml in a total fluid quantity of 10L. Certainly to me something that would make little difference to the performance of the transmission if the level was measured at a temp other than the spec.

 

[jjrichar]

Yes I'm calling incorrect on that statement too, based on seeing the difference just today.

To say that a gearbox that holds 9L can go with 2L less (22%) is just not good advice at all, and could lead to expensive repairs or at best early wear.

OP, you need the correct fluid filled to the correct level. That goes for any fluid filled aspect of any car. You wouldn't run the motor with 22% less oil.

I think people are misunderstanding my post. I absolutely am not suggesting that people don't fill the transmission correctly. My comments were only related to diagnosis of the problem the OP was having and not having him waste his time diving down a hole that wasn't going to solve the problem.

From my perspective the symptoms he was providing had nothing to do with fluid level. When the problem happens driving gently straight ahead and not driving hard I believe it's impossible for the problem to be related to low fluid level and the filter intake being uncovered.

For what it's worth, I think his diagnosis of the TC clutch as he states above are possibly correct, but a lot more diagnosis needs to be done.

 

[Anticdubai]

I got ZF to check my fluid level and test as service on monday. I'll keep you guys up to date if there is any progression.

That is interesting feedback. The testing I did wasn't underfilling and then driving, but accurately measuring the expansion of the fluid (in a test tube) as the temp rose from 40C to 100C. To be honest it was barely noticeable. Less than 1%. ie Less than 100ml in a total fluid quantity of 10L. Certainly to me something that would make little difference to the performance of the transmission if the level was measured at a temp other than the spec.

I think it isn't because of expansion of fluid, but because on hotter transmission it being pumped differently and therefore reaches filling level hole with less volume.

 

[azadani]

I think people are misunderstanding my post. I absolutely am not suggesting that people don't fill the transmission correctly. My comments were only related to diagnosis of the problem the OP was having and not having him waste his time diving down a hole that wasn't going to solve the problem.

From my perspective the symptoms he was providing had nothing to do with fluid level. When the problem happens driving gently straight ahead and not driving hard I believe it's impossible for the problem to be related to low fluid level and the filter intake being uncovered.

For what it's worth, I think his diagnosis of the TC clutch as he states above are possibly correct, but a lot more diagnosis needs to be done.

Each to their own mate, no angst intended.

My thoughts are that checking the level/type of fluid would be the first check because it's free. I personally don't agree that a lower level can't cause these symptoms, I certainly think they could, but checking them to be correct would eliminate that possibility wrong or right.

I worry for the OP going back to the same place, as they're likely to say what they did was right and he needs a new gearbox. I wonder if he's not better off putting it on stands and checking it himself using the guides here. If it was wrong he could pick up a bottle of the same stuff on his recent receipt and top it off for starters before pulling the trans out.

I've just done mine and I do suspect it was low, based on the amount I took out and put back in and the sheer bodgeyness of every single thing that the previous mechanic did. Fair enough it's brand new fluid, but the old stuff wasn't terrible and the car is driving considerably better.

I come from a fault finding work background, and find it's best to start with the simple things, and highly suspect if the faulty item has just been worked on. To recheck the level may not be the solution, but surely it's the first step?

Mind you, I just today almost crapped my pants because I thought my AC condensation drain was coolant in my gearbox somehow, so take what I say as you will...

 

[azadani]

I think it isn't because of expansion of fluid, but because on hotter transmission it being pumped differently and therefore reaches filling level hole with less volume.

You mean viscosity when hot? Most likely and almost certainly that's a factor. Looking at the stuff that drips out of the fill port with it running, it's also looks like it's been agitated pretty heavily as well if that makes a difference.

 

[Anticdubai]

You mean viscosity when hot? Most likely and almost certainly that's a factor. Looking at the stuff that drips out of the fill port with it running, it's also looks like it's been agitated pretty heavily as well if that makes a difference.

And viscocity as well.

 

[MrMCar]

Test tubes With all due respect, you guys are making a mountain out of a molehill.

I've been changing transmission fluid/filters a very long time. It's really simple.
Drop the pan, drop the filter, wash the inside of the pan. Take care of the gasket (whatever blows your skirt up) and reinstall.
Fill it cold till it starts to trickle out, put fill plug in one thread. Start the car (just leave it in park damnit) and immediately fill until it overflows. Be fast and have the fill plug in one hand before removing the filler tube. Swap and make hand tight. Shut off the car, then get back under and finish up tightening and spraying/wiping.

More transmission issues have been created by ambiguous filling/underfilling. If it's slightly overfilled ambiguity is completely removed and it creates no harm.
Simple.
KISS, keep it simple stupid.

 

[azadani]

Test tubes With all due respect, you guys are making a mountain out of a molehill.

I've been changing transmission fluid/filters a very long time. It's really simple.
Drop the pan, drop the filter, wash the inside of the pan. Take care of the gasket (whatever blows your skirt up) and reinstall.
Fill it cold till it starts to trickle out, put fill plug in one thread. Start the car (just leave it in park damnit) and immediately fill until it overflows. Be fast and have the fill plug in one hand before removing the filler tube. Swap and make hand tight. Shut off the car, then get back under and finish up tightening and spraying/wiping.

More transmission issues have been created by ambiguous filling/underfilling. If it's slightly overfilled ambiguity is completely removed and it creates no harm.
Simple.
KISS, keep it simple stupid.

Did this just yesterday and it seemed good. Trans is working better than it was.