07-10-2018, 03:25 PM | #1 |
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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? |
07-10-2018, 04:14 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, 06:16 PM | #3 | |
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07-10-2018, 06:47 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, 07:13 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, 12:42 PM | #6 | |
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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, 12:43 PM | #7 |
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07-11-2018, 01:59 PM | #8 | |
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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, 07:47 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, 12:12 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, 08:26 AM | #11 | |
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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, 11:40 AM | #12 | |
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07-13-2018, 11:59 AM | #13 | |
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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, 02:09 PM | #14 | |
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07-13-2018, 04:45 PM | #15 | |
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07-13-2018, 05:28 PM | #16 |
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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, 06:17 PM | #17 | |
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07-21-2018, 10:57 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, 08:34 PM | #19 | |
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07-22-2018, 09:46 AM | #20 | |
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07-23-2018, 01:31 PM | #21 |
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07-23-2018, 06:32 PM | #22 | |
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- 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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