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      07-10-2018, 04:25 PM   #1
kalien34
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F36 430i low speed transmission jerk - compared to Subaru

Old topic I know. But I drove my uncle's Subaru Legacy for 20 ish miles and noticed that its gearbox is actually smoother than my F36..........

Particularly from a stand still start the throttle is very light and responsive, the car tends to be very lively from the get go. (Of coz on free way speed it's not comparable to the 2.0L turbo engine)

Most importantly, there very minimal or even unnoticeable jerk/hesitation in low speed (between 1st and 2nd) compared to the F36!!! Once I got off the ramp from the free way, merged onto the local traffic in front a light. The original lane had a long line, and therefor I slowed down to get ready for a stop, then realized the next lane is pretty much free then I pull into it and stepped hard onto the pedal. In my normal experience with the F36, such a sudden hard acceleration from a very low speed will almost definitely result in a jerky acceleration. Almost every time I step hard on the pedal when the car was about to fully stop the tranny would be in between gears which creates the jerkiness.

But no, not in the Legacy... It was fast yet smooth and I almost can't even feel the gear change... Oh my....

Anyone had similar experience? Since the 2 cars gave me very different feeling I know it wasn't my driving style... Is it related to the adaptive throttle? Does resetting it help?
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      07-10-2018, 05:14 PM   #2
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I don't think it's in your head. My mom has a Subaru Legacy (NA 4 cyl, AWD) and I've driven it a few times - it's smoother at lower speeds than my BMW. I know the exact scenario you're describing, I can't get my BMW to feel as smooth no matter what mode I'm in or how I play with the throttle.

Maybe the CVT? NA vs Turbo? AWD vs RWD? I'd be curious too
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      07-10-2018, 07:16 PM   #3
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Quote:
Originally Posted by TF3090 View Post
I don't think it's in your head. My mom has a Subaru Legacy (NA 4 cyl, AWD) and I've driven it a few times - it's smoother at lower speeds than my BMW. I know the exact scenario you're describing, I can't get my BMW to feel as smooth no matter what mode I'm in or how I play with the throttle.

Maybe the CVT? NA vs Turbo? AWD vs RWD? I'd be curious too
Didn't think about CVT, and Yes most likely that plays a big factor. My previous IS250 6AT had the same jerkiness so I guess the ZF8 is not alone in the AT tranny arena. I'll try the adaptive reset tomorrow and see if it helps at all.
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      07-10-2018, 07:47 PM   #4
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You are comparing 2 totally different cars. Different engines, different transmissions, etc etc. Not only that, if the Subaru has a CVT then its even way more off of a comparison.

That is like saying, "My tractor does not shift like my Ferrari....."
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      07-10-2018, 08:13 PM   #5
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The 8AT has uses a lock-up torque converter and it keeps it locked down to low travel speeds. It will feel like a manual transmission during these times and is normal.
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      07-11-2018, 01:42 PM   #6
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Quote:
Originally Posted by kalien34 View Post
Old topic I know. But I drove my uncle's Subaru Legacy for 20 ish miles and noticed that its gearbox is actually smoother than my F36..........

Particularly from a stand still start the throttle is very light and responsive, the car tends to be very lively from the get go. (Of coz on free way speed it's not comparable to the 2.0L turbo engine)

Most importantly, there very minimal or even unnoticeable jerk/hesitation in low speed (between 1st and 2nd) compared to the F36!!! Once I got off the ramp from the free way, merged onto the local traffic in front a light. The original lane had a long line, and therefor I slowed down to get ready for a stop, then realized the next lane is pretty much free then I pull into it and stepped hard onto the pedal. In my normal experience with the F36, such a sudden hard acceleration from a very low speed will almost definitely result in a jerky acceleration. Almost every time I step hard on the pedal when the car was about to fully stop the tranny would be in between gears which creates the jerkiness.

But no, not in the Legacy... It was fast yet smooth and I almost can't even feel the gear change... Oh my....

Anyone had similar experience? Since the 2 cars gave me very different feeling I know it wasn't my driving style... Is it related to the adaptive throttle? Does resetting it help?
ECO mode is the jerkiest of them all on my F36. I really mean it. Occasionally it would JERK so damn hard during throttle application that my teeth begin shaking ..

Taking it to a local dealer in a month for the first oil change [approaching 7k - and did do mid-interval change myself @ 3000 miles] and will be addressing it. Not sure if its just a nature of the car's transmission system/ software update or an underlying issue. It's been like this from the day 1.
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      07-11-2018, 01:43 PM   #7
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Quote:
Originally Posted by Wires View Post
The 8AT has uses a lock-up torque converter and it keeps it locked down to low travel speeds. It will feel like a manual transmission during these times and is normal.
Interesting. Any source where I can read up more on it ?
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      07-11-2018, 02:59 PM   #8
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Originally Posted by Wires View Post
The 8AT has uses a lock-up torque converter and it keeps it locked down to low travel speeds. It will feel like a manual transmission during these times and is normal.
Not sure if I understand this correctly. The torque converter is to prevent too much slippage between the engine and the transmission, and thus when you say it feels like a manual you mean the power transfer would be much more direct without losing power during transmission.

But how does that relate to the jerkiness or hesitation upon stepping on the pedal? It feels like when the pedal is pushed the tranny hesitates for a split second with not much power, and then suddenly the power comes and gives me a kick on the butt...
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      07-12-2018, 08:47 PM   #9
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There is a clutch in the converter that eliminates slippage. When it's unlocked, the torque converter has variable ratio until higher RPMs (when you hold the brake and apply the gas, it will rev until the converter reaches fluid lock), and the revs will stop climbing.

To aid in mileage, the mechanical clutch is engaged which couples the engine directly to the transmission like a manual. In other vehicles, it unlocks at a higher RPM. On this transmission, it keeps it locked right down close to idle. It gives you that "chug chug chug" effect if the revs are low and you start to load the engine.


Your hesitation/power burst could just be that the engine has less power at lower revs, and if it's really hot out, it is even lower. Once the engine revs up a bit, then you get specified torque out of it, hence the burst.
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      07-13-2018, 01:12 AM   #10
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Put car in sport mode all the time would solve the problem. The default mode tran, so called comfort is totally trash. It was there to pass some weird test EU put out but no one deserve to use it in real life.
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      07-13-2018, 09:26 AM   #11
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Quote:
Originally Posted by Cyanfall View Post
Put car in sport mode all the time would solve the problem. The default mode tran, so called comfort is totally trash. It was there to pass some weird test EU put out but no one deserve to use it in real life.
I only drive in sport mode. I realized it could be due to the throttle delay after reading some reviews on Sprint Booster, as people mentioned that helps solve the issue.

As the feeling is like the initial press on the pedal doesn't generate much response from the engine, but then suddenly the power comes.
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      07-13-2018, 12:40 PM   #12
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Originally Posted by kalien34 View Post
I only drive in sport mode. I realized it could be due to the throttle delay after reading some reviews on Sprint Booster, as people mentioned that helps solve the issue.

As the feeling is like the initial press on the pedal doesn't generate much response from the engine, but then suddenly the power comes.
Since i have never driven 430 or subaru before, I actually do not really understand the situation. I felt the throttle response in sport mode of 440 is fast enough, probably I was wrong and subaru is even faster. Someday i should have a try.
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      07-13-2018, 12:59 PM   #13
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Quote:
Originally Posted by Cyanfall View Post
Since i have never driven 430 or subaru before, I actually do not really understand the situation. I felt the throttle response in sport mode of 440 is fast enough, probably I was wrong and subaru is even faster. Someday i should have a try.
It's like a short time after you put your foot on the throttle, the car doesn't respond immediately. Instead after that short while the power came and it creates a kick on you. It doesn't happen often especially if you be gentle on the throttle. But if you are at a very low speed but put your foot down in a sudden, it could happen.

While in the Legacy, your foot down, the car reacts, seamlessly. CVT must be a big factor, and I am thinking thorttle delay could be another, because the ECU is taking time to respond to the throttle motion and during that time you thought the power is not enough that's why the car is not responding therefore you tend to step on the pedal further, but once the signal processed by the ECU the throttle becomes too much already and thus created the kick/jerk.
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      07-13-2018, 03:09 PM   #14
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Quote:
Originally Posted by kalien34 View Post
It's like a short time after you put your foot on the throttle, the car doesn't respond immediately. Instead after that short while the power came and it creates a kick on you. It doesn't happen often especially if you be gentle on the throttle. But if you are at a very low speed but put your foot down in a sudden, it could happen.

While in the Legacy, your foot down, the car reacts, seamlessly. CVT must be a big factor, and I am thinking thorttle delay could be another, because the ECU is taking time to respond to the throttle motion and during that time you thought the power is not enough that's why the car is not responding therefore you tend to step on the pedal further, but once the signal processed by the ECU the throttle becomes too much already and thus created the kick/jerk.
I think I can help explain your situation. First off, the CVT in the Subaru will certainly aid at low speed/coasting throttle application as I found in my 2013 Altima. But the main culprit in the delay you're feeling is the B48 engine. I had a MY2014 328i with the N26 engine and I never had an issue with throttle response while coasting, or low speed throttle response. In my 2017 with the new B48 engine, there is a pronounced delay when accelerating from a low speed coast. The B48 is simply not able to provide the needed torque at low RPMs that the N20/N26 did. The N20 produces max. torque at 1250 RPM while the B48 does so at 1450 RPM. Putting the drive mode to sport should help quite a bit but of course you'll use more fuel.
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      07-13-2018, 05:45 PM   #15
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Quote:
Originally Posted by kalien34 View Post
It's like a short time after you put your foot on the throttle, the car doesn't respond immediately. Instead after that short while the power came and it creates a kick on you. It doesn't happen often especially if you be gentle on the throttle. But if you are at a very low speed but put your foot down in a sudden, it could happen.
That sounds more like a bit of turbo lag (normal) and nothing to do with the transmission.....
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      07-13-2018, 06:28 PM   #16
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Originally Posted by YasM3 View Post
That sounds more like a bit of turbo lag (normal) and nothing to do with the transmission.....
Absolutely. I do suspect that BMW changed (or revised) the turbocharger when switching from the N20 to the B48 engine as part of their constant cost cutting. When I first drove the 330i with the B48, the first thing I noticed was they tuned the drivetrain so that the 1-2 shift is performed at higher RPM than the N20-fitted cars, presumably to aid performance when equipped with the B48. This may be one of the reasons why the B48 is less fuel efficient.
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      07-13-2018, 07:17 PM   #17
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Quote:
Originally Posted by LMK5 View Post
Absolutely. I do suspect that BMW changed (or revised) the turbocharger when switching from the N20 to the B48 engine as part of their constant cost cutting. When I first drove the 330i with the B48, the first thing I noticed was they tuned the drivetrain so that the 1-2 shift is performed at higher RPM than the N20-fitted cars, presumably to aid performance when equipped with the B48. This may be one of the reasons why the B48 is less fuel efficient.
Well said. I sort of noticed the same thing.
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      07-21-2018, 11:57 AM   #18
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So I've tried putting the tranny in DS mode so that i can see the gear position and how it changes. Confirmed the lag/hesitation didn't come from gear changes, as the lag is still presence while gear remains in either 1 or 2.
It all comes down to either throttle delay or turbo lag. Order a cheap cheap throttle booster on eBay from China (not willing to spend $300 bucks for SB as it's really not rocket science i'm sure). Will see how much it could improve.
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      07-21-2018, 09:34 PM   #19
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Quote:
Originally Posted by LMK5 View Post
Absolutely. I do suspect that BMW changed (or revised) the turbocharger when switching from the N20 to the B48 engine as part of their constant cost cutting. When I first drove the 330i with the B48, the first thing I noticed was they tuned the drivetrain so that the 1-2 shift is performed at higher RPM than the N20-fitted cars, presumably to aid performance when equipped with the B48. This may be one of the reasons why the B48 is less fuel efficient.
The turbo in B series engines are much larger than previous gen for more torque. N55 and N20 were using probably smallest turbos bmw ever used, which reduced lag.
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      07-22-2018, 10:46 AM   #20
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Quote:
Originally Posted by kalien34 View Post
So I've tried putting the tranny in DS mode so that i can see the gear position and how it changes. Confirmed the lag/hesitation didn't come from gear changes, as the lag is still presence while gear remains in either 1 or 2.
It all comes down to either throttle delay or turbo lag. Order a cheap cheap throttle booster on eBay from China (not willing to spend $300 bucks for SB as it's really not rocket science i'm sure). Will see how much it could improve.
Well that is a waste of money. Its clearly turbo lag. Use sport mode and the correct RPM, no lag.
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      07-23-2018, 02:31 PM   #21
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Quote:
Originally Posted by Cyanfall View Post
The turbo in B series engines are much larger than previous gen for more torque. N55 and N20 were using probably smallest turbos bmw ever used, which reduced lag.
I see. So what is the advantage of the B48 vs. the N20? The N20 felt better to me.
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      07-23-2018, 07:32 PM   #22
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Quote:
Originally Posted by YasM3 View Post
Well that is a waste of money. Its clearly turbo lag. Use sport mode and the correct RPM, no lag.
Don't agree. I've had this same issue (with throttle tip in delay). It's been reported with different BMW engines and auto trans. I've got a N55 w/ 8HP. It appears some cars (and people) are more sensitive to it than others. Why do I think it's not turbo?
- Many cars have turbos, they don't all behave this way
- If you do the throttle adaptation reset, it's not as bad (but soon comes back)
- It's still there in Sport mode, but not as noticeable
- People here have reported success with Sprint Booster, etc

I mostly live with it, but it is damn annoying at times. Was thinking about Sprint Booster, but also wanted a tune, so recently added the MHD stage 1 tune. Was hoping the delay would go away or not be as bad, but it's about the same.

OP, try this throttle adaptation reset and let us know what you think:
- Foot off brake
- Press start to turn on car (but not start)
- Press accelerator pedal to floor for about 30-40 seconds
- Press start to turn off car
- Release accelerator
- Wait about 2 minutes, then start normally and drive off
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