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Long story short, car is a BMW 530d automatic from 2012 with the ZF 8 HP transmission. The problem is, after the timing chain was replaced, 2 years ago (and transmission pullet out to do that), the car started exhibiting hard shifts especially on 1st to 2nd gear gear, significantly more pronounced when engine/transmission are cold. There have never been any errors (with diagnostic software) and 1-2 shifts were initially a very hard slam, especially at very low acceleration. Changed fluid and filter - it was in very good condition - now less harsh shifts

Current behaviour:

  • Feeling shifts 1-2, 2-3, 3-4: 1-2 shift being harder than the other: acceleration drops (feel the car braking) then slammed from behind - independent of how heavy or light I am with the gas pedal. After several miles of driving shifting becomes very smooth on Comfort mode (still hard 1-2 shifts on Sport). Shifting is always hard 1-2 if I keep the acceleration constant to have a higher rpm (say 3000) then manually shift to 2nd.

  • At idle acceleration, if I manually shift from 1st to 2nd I can feel a clutch hooking onto something - makes the car jerk/vibrate a few times.

  • Feel torque converter locking up in gear 1: at slight constant acceleration (1200 rpm) I can feel a pulse (several times) which is slightly pushing the car forward. I had taken the car to a transmission shop, they decided it was a valve body issue and replaced it with a "new" one, tested it: instead of the pulse there was now a hard slam from behind when reaching around 1200 rpm in gear 1 (without shifting gears, at very very slow acceleration) - torque converter?? They put the original valve body back.

  • When braking and coming to a stop - same feeling of a clutch hooking onto something - makes the braking nonlinear - happens even if I'm in gear 1, accelerate to gain over 1200 rpm than apply brakes.

  • Lurching - happens sometimes when I've just stopped the car completely - 1 second after, for a brief moment the car wants to move forward - the brakes keep it from doing so.

Symptoms get better after driving a lot, long after the engine/transmission has reached the operating temps. And it also seems to get better if shut off the engine a few times. Now, I know this transmission has the torque converter engaging early, from gear 1 and it's pulse operated.

Can you help me? It's the transmission or the torque converter?

  • You might try to do a ECU reset by disconnecting the battery for about a 1/2 hour. Sometimes the ECU (or TCU if so equipped) might get in a bad state. By resetting it, it might decide it wants to play fair again. I know this is akin to telling someone to reboot their workstation to solve an issue, but it is a good first step in the diagnostic chain. – Pᴀᴜʟsᴛᴇʀ2 Dec 20 '18 at 17:13

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