Clunk when slowing down

[Zimm]

This is good ammunition as I believe it is t-case preload. We’ll have to focus on this one issue until resolved.

It only does it on 3-2 and not all the time. It never does it anywhere else. I'm not grasping how it can be the t-case preload. On a really bad shift, I can feel it when 3rd is released as it gives the illusion of acceleration because its no longer decelerating, and I can fell the second grab. You'll have to explain your assessment that to me. I think its the programming.

 

[Dopplemax]

Knock on wood, I haven't had this issue...yet. The wife's 2023 Escalade V had what sounds like a similar condition that the dealer(s) kept telling us was normal. Finally got one of them to take it apart and they found the clutch plates in the TC were slipping. Replaced the plate shims with a different thickness and it went away completely. So we traded it in lol on a 2025 non-V that doesn't have the full time AWD nor 685 HP. So far so good.

 

[BrianK]

Any updates on this issue or additional repair and warranty experience? I am still having the clunking problem from 3-2, but also when coming on and off throttle at times, low speeds, 2nd gear typically. The severity has lessened. It seems almost like slop in the driveline. I suspect the T-Case based on previous comments. It’s a: throttle on, fraction of a second, then clunk; throttle off, fraction of a second, then clunk.

 

[NQ94]

Any updates on this issue or additional repair and warranty experience? I am still having the clunking problem from 3-2, but also when coming on and off throttle at times, low speeds, 2nd gear typically. The severity has lessened. It seems almost like slop in the driveline. I suspect the T-Case based on previous comments. It’s a: throttle on, fraction of a second, then clunk; throttle off, fraction of a second, then clunk.

The performance ZF transmission groups and transmission tech groups have mentioned 3-2 down shift and a 6-7 upshift noise and poor quality shifts in some 8HP transmissions in other car brands. Some of the repairs suggested were for the dealer reset the trans back to default settings and let it readapt/relearn, servicing and checking the pan and removing valve bodies for inspection and checking the separator plates. ZF does not seem to suffer the separator plate and valve body issues the GM 10 speed has but it does have its own faults.
The best bet would be taking the car to a transmission shop that specialises in ZF transmissions for a second opinion, they're more likely to have the tools and experience to test the transmission properly.

 

[AWo]

It seems to be about the adaptation values. These are self-learned values by the gearbox ECU to optimize the shifting. They adjust to wear and tolerances over time.
They are responsible for the clutch pressures generated by valves of the various clutches in the gearbox, the speed to pre-load a clutch, the shifting itself and the holding pressure.

If the gearbox is new, a reset leads to re-learning. So shifting should become better over time. If the gearbox is in use for quite a time the small filters of the valves can be clogged and the adaptions values become incorrect. This can not be fixed by flushing the gearbox! You have to dismantle these valves and clean them.

Sometimes it is worth to measure the adaption values to get a clear picture of the issues.

AWo

 

[Tom109]

Sometimes it is worth to measure the adaption values to get a clear picture of the issues.

AWo

How is this accomplished?

 

[AWo]

How is this accomplished?

You need the right equipment and the intended values for that, it is a work shop thing.....so go and find a work shop which is specialised in ZF gearboxes or automatic gearboxes...

AWo

 

[Zimm]

The performance ZF transmission groups and transmission tech groups have mentioned 3-2 down shift and a 6-7 upshift noise and poor quality shifts in some 8HP transmissions in other car brands. Some of the repairs suggested were for the dealer reset the trans back to default settings and let it readapt/relearn, servicing and checking the pan and removing valve bodies for inspection and checking the separator plates. ZF does not seem to suffer the separator plate and valve body issues the GM 10 speed has but it does have its own faults.
The best bet would be taking the car to a transmission shop that specialises in ZF transmissions for a second opinion, they're more likely to have the tools and experience to test the transmission properly.

resetting didnt do anything.

 

[Tom109]

@Zimm - is your 3-2 the same? For the most part mine is the same clunk, but speed dependent it is quieter or even absent. I need to log the speed/clunk differences - it still really bothers me. I’m going to open a case direct with IA.

 

[NQ94]

It seems to be about the adaptation values. These are self-learned values by the gearbox ECU to optimize the shifting. They adjust to wear and tolerances over time.
They are responsible for the clutch pressures generated by pistons of the various clutches in the gearbox, the speed to pre-load a clutch, the shifting itself and the holding pressure.

If the gearbox is new, a reset leads to re-learning. So shifting should become better over time. If the gearbox is in use for quite a time the small filters of the hydraulic pistons can be clogged and the adaptions values become incorrect. This can not be fixed by flushing the gearbox! You have to dismantle these pistons and clean them.

Sometimes it is worth to measure the adaption values to get a clear picture of the issues.

AWo

Are the small screens that you are referring to for the solenoids (ERPS) on the mechatronics module?

 

[AWo]

Are the small screens that you are referring to for the solenoids (ERPS) on the mechatronics module?
View attachment 7899514

Screens....? I do not understand (the question), can you explain, please?

AWo

 

[Zimm]

@Zimm - is your 3-2 the same? For the most part mine is the same clunk, but speed dependent it is quieter or even absent. I need to log the speed/clunk differences - it still really bothers me. I’m going to open a case direct with IA.

It changes depending on the circumstances. its NOT the tcase. I cannot replicate it in 3-4 and above.

I can actually make it "clunk" slowly. In an empty lot, I get the car into third, and let it drift down. It holds gear almost like a stick in third, then I can feel it release third, and since its not slowing as much because it's actually hanging in neutral for 1/2 second, it gives the sensation of speeding up, and then it suddenly grabs second. Now, if I time that right, I can touch the throttle and it will clunk. Basically, there's a weird delay in the shift.

I'm having a hard time telling if its the "A" clutch that engages for 1 and 2, or the tq converter not having enough slip, or a sticky solenoid, or maybe a combo of issues that is exacerbated due to the excessive way they have the transmission set up to hold gear and slow the truck, because when I come to a stop, there are times the car vibrates until I feel a pop as it releases first. It's fucked up.

 

[AWo]

Are the small screens that you are referring to for the solenoids (ERPS) on the mechatronics module?
View attachment 7899514

Ahh, now I see. Yes, that is what I meant, but I used the wrong term. I wrote piston (corrected already) but I meant valve.

AWo

 

[NQ94]

This is a very basic summary, ZF 8HP has a well packaged compact design and would have one of the most complex gear flows to explain. Looking at an 8HP gear sequencing changing from from 3rd to 2nd the transmission is going from one brake and two clutches in 3rd to 2 brakes and one clutch in second, using euro transmission terminology. US terms a brake as a holding clutch holding generally the planetary ring gear but may hold another planetary element to the transmission case whereas the clutch holds two rotating elements together. During a coast to stop the transmission line pressure (main pressure) will be near the lowest pressure to allow for a softer slower shift. A sudden throttle up during the shift will be detected quickly by the software with the hydraulic system being slower to react, the electronics will also detect this with input and output speed differences not meeting the algorithm and likely ramp up the engagement oil supply to the oncoming clutch to engage quicker and firmer to reduce slip. As you come to a stop, assuming a rolling stop, it's more so the lockup disengaging, this is also assuming the Grenadier TCM is programmed more towards a commercial vehicle then a passenger car which would drop or slip the lock up earlier for comfort. TC lock up can be controlled in any forward gear and has three states, engaged, disengaged and controlled slip. First gear only releases when stopped in gear foot on brake by keeping one clutch engaged, releasing one clutch and control slipping the third clutch required to deliver drive, this is to reduce fuel use, NIC neutral idle control.
It will be interesting to see if some of the new Cummins 6.7 gas engine and ZF Powerline 8 speed (big version of the Grenadier 8HP) in the new RAM trucks will share similar shift quality issues.

Images of ZF 8HP 45 for reference. The basic construction and operation remain the same over the models and generations with changes in ratios and component sizes.

 

[Zimm]

This is a very basic summary, ZF 8HP has a well packaged compact design and would have one of the most complex gear flows to explain. Looking at an 8HP gear sequencing changing from from 3rd to 2nd the transmission is going from one brake and two clutches in 3rd to 2 brakes and one clutch in second, using euro transmission terminology. US terms a brake as a holding clutch holding generally the planetary ring gear but may hold another planetary element to the transmission case whereas the clutch holds two rotating elements together. During a coast to stop the transmission line pressure (main pressure) will be near the lowest pressure to allow for a softer slower shift. A sudden throttle up during the shift will be detected quickly by the software with the hydraulic system being slower to react, the electronics will also detect this with input and output speed differences not meeting the algorithm and likely ramp up the engagement oil supply to the oncoming clutch to engage quicker and firmer to reduce slip. As you come to a stop, assuming a rolling stop, it's more so the lockup disengaging, this is also assuming the Grenadier TCM is programmed more towards a commercial vehicle then a passenger car which would drop or slip the lock up earlier for comfort. TC lock up can be controlled in any forward gear and has three states, engaged, disengaged and controlled slip. First gear only releases when stopped in gear foot on brake by keeping one clutch engaged, releasing one clutch and control slipping the third clutch required to deliver drive, this is to reduce fuel use, NIC neutral idle control.
It will be interesting to see if some of the new Cummins 6.7 gas engine and ZF Powerline 8 speed (big version of the Grenadier 8HP) in the new RAM trucks will share similar shift quality issues.

Images of ZF 8HP 45 for reference. The basic construction and operation remain the same over the models and generations with changes in ratios and component sizes.
View attachment 7899585View attachment 7899594

That’s my “worry”. That It has to do with how this transmission is reacting to the programming, and there’s enough variability with these units that some end up shifting like shit. The thing is, this doesn’t have the payload capability to even consider utilizing the transmission in this way. It’s just overkill. This is still basically a car.

They really didn’t test this truck out much to see if all their ideas were practical in application. If my truck is facing down hill when I start it and pull out, it won’t upshift. Drifting up to the 20mph speed limit has the engine howling. I have to step on the gas pointing down a steep Pittsburgh street, and then jump on the brake. Stooopid. I can push a button on my diesel f350 and have it act similar, but it’s driver activated for the situation. Wtf good does that do me in the Ineos?

There are shops that reprogram the shifting in bmw’s for the “sporty” type owners. I wonder if they can make this act more like a car, or if a TCU or whatever controls this tranny, and be swapped in from a regular old x5. I drive in traffic jams every day, and shifting to N all the time is a bigger pain than my h55f.

 

[Tom109]

I need to find someone local that has @NQ94 knowledge of the 8spd.

 

[Zimm]

I need to find someone local that has @NQ94 knowledge of the 8spd.

Amen. I’ve been internetting for months and watched quite a few zf8 vids, and he had more data in 2 hours.

 

[HereinDaRockies]

That’s my “worry”. That It has to do with how this transmission is reacting to the programming, and there’s enough variability with these units that some end up shifting like shit. The thing is, this doesn’t have the payload capability to even consider utilizing the transmission in this way. It’s just overkill. This is still basically a car.

They really didn’t test this truck out much to see if all their ideas were practical in application. If my truck is facing down hill when I start it and pull out, it won’t upshift. Drifting up to the 20mph speed limit has the engine howling. I have to step on the gas pointing down a steep Pittsburgh street, and then jump on the brake. Stooopid. I can push a button on my diesel f350 and have it act similar, but it’s driver activated for the situation. Wtf good does that do me in the Ineos?

There are shops that reprogram the shifting in bmw’s for the “sporty” type owners. I wonder if they can make this act more like a car, or if a TCU or whatever controls this tranny, and be swapped in from a regular old x5. I drive in traffic jams every day, and shifting to N all the time is a bigger pain than my h55f.

How do you shift to N while driving? I am always afraid of the pushing it beyond N into R..

I know it’s all software controlled so it shouldn’t do that, but it’s hard to overcome that fear

 

[Zimm]

How do you shift to N while driving? I am always afraid of the pushing it beyond N into R..

I know it’s all software controlled so it shouldn’t do that, but it’s hard to overcome that fear

just push it forward. you can return to drive if moving fast enough, otherwise you need to tap the brake to reengage. I'm sure it'll take NQ94 17 seconds of research to tell us what that MPH limiter is set at.

As far as computer cut out, I dunnkow. Mine will pop into park before a complete stop. I got a little ahead of myself and found that out while parking. I was hardly moving, but it was enough to elicit and OPPS out of me.

 

[NQ94]

I need to find someone local that has @NQ94 knowledge of the 8spd.

I wouldn't call myself an expert in the 8sp field but have had considerable past field service and overhaul experience with ZF and Allison heavy commercial vehicle automatic transmissions. Nearly all automatic transmissions and their electronic controls function basically the same way requiring the same input and output data, have similar hydraulic control principals and share similar customer described faults. The 8HP has always piqued my interest from when it was released because of its complexity and now because of the growing following and support for the ZF 8HP in the conversion and performance industry.
A good auto transmission tech will have a good understanding or will be willing to learn how engine, transmission and electronic components interact and a genuine interest in auto transmissions.