Erratic Shifts on Turns

[ltemup4650]

Hello all. I’ve completed some serious work (Everything from stuff as simple as brakes all the way to engine rebuilds) on over 50 cars in my lifetime. I’m having an issue that has me absolutely stumped. I’ll be as descriptive as possible with my issue.

Background: A couple months ago, I bought a 2011 BMW X5 with a bad ZF 8HP45 transmission. Upon pulling the pan it was confirmed to be a mechanical failure (metal bits in the pan). I replaced the transmission from a donor (wrecked) 2011 X5. I removed the valve bodies from both the bad and donor transmissions. I then removed the mechatronics from the bad transmission and installed it on the new one’s valve body since they’re married to the DME.

Issue: From a stop, on all of the time on left hand turns, and sometimes right hand turns: the vehicle takes off fine, but as the turn starts has erratic shifts. It’s almost like the engine dies and then comes back to life with a jerk. It is not slipping (i.e. the engine RPMs do not climb without the vehicle accelerating).

Facts:
-The transmission was filled per the ISTA procedure.
-No check engine light, pending, or stored codes.
-Shifts in a straight line at all different applications of the throttle (quick starts; slow starts) are perfect.
-If I manually select the gears using the M/S option, the issue remains.
-With stability control off (DSC), the issue remains
-I completed the steering angle calibration using ISTA
-I changed the fluid in the transfer case and performed the calibration using ISTA
-I removed the front driveshaft and took it for a drive. Issue remained.

My thoughts:
-It sure feels like a classic case of a trans with low fluid (fluid sloshes away from the pickup on turns). But, I filled it per the procedure.
-Steering angle sensors can soft fail and cause weird transmission shifts. I would think, however, that with the DSC off it would take the steering wheel angle sensor out of the equation. I’ll probably still unplug it and see if the issue remains.
-Wheel speed sensors can also cause weird shifting, but they would likely through a trouble light.
-The TCM (mechatronics) could be bad, but again, I would think that a trouble code would be in.

Without a trouble code, I’m at a loss. Any thoughts from the community?

[ard]

odd one. No great ideas...wiring harness/cable getting stressed on turns?


FWIW: https://bimmerscan.com/products/bmw-...f-6hp-8hp-dct/

[ltemup4650]

ARD,

Very odd.

I edited my original post. I thought it didn't have an issue when I manually shifted it, but I discovered this morning that that is untrue. The issue remains even with manual shifts.

I will say, if I take left turns super slow, it is fine. The more I think about it, it has to be fluid suction related. It makes the most sense because it is most prominent on left turns vs. right. Since the pump's suction is forward and to the left in the transmission, accelerating forward and turning left would move the fluid away from the suction tube the most. What I don't understand though, is the transmission is full. I double checked it even. It could be a bad pan (with integrated filter) that has a manufacture defect baffle.

[B4_685]

Very interesting - not sure it matters but I do recall a specific re-learn for the 6HP which I believe doesnt apply to the 8hp - have you tried contacting zf directly?

Was thinking speed sensors when you mentioned it - any chance one could be faulty on the rear wheels causing a sensed wheel spin and subsequent brake application? Dunno if unplugging one or both sensors could be an option to test...

Edit: I dont know specifically about BMW’s but other manufacturers still have some active diff input even though you switch the traction/stability programs off - maybe unplug the abs pump? That’ll obviously upset the dme a bit but I dont know how else other than unplugging a wss to disable the input (yaw sensor in jeeps also works)

2012 E70 N63 50i

[ard]

Maybe starting to sound like a transfer case issue.... do some research, very odd, jerky stuff when not mvoing straight ahead.

Ill search later, but here or BF..definitely something to be found

[smassey321]

Originally Posted by ard

Maybe starting to sound like a transfer case issue.... do some research, very odd, jerky stuff when not mvoing straight ahead.

Ill search later, but here or BF..definitely something to be found

+1 on this. Pull the fuse for the TC controller and see if the issue is still there.

[CLS70]

I have had a similar issue; it comes/goes but is basically a hesitation when accelerating during slow turns -

lets say I'm getting into an intersection to make a right turn, if I slow down but do not come to a full stop -to let the car start turning just with the impulse/inertia- when I accelerate to complete the turn and keep going, the car hesitates for a moment before accelerating, it does not jumps or downshifts, is just like a 1/2 second delay....

I looked for the transfer case issue across few posts but never came to find what was the fuse to remove or how to disconnect the AWD......

Left Turns (=into oncoming traffic) normally require a full stop so the issue does not show up and if I make the full stop in Right turns (e.g. due traffic), it does not happen either so it only happens occasionally.....note that for the issue to happen, the turns needs to start with good impulse/momentum already (which could mean a fluid gets push to the side) at one moment, I though it could be water or something going sideways and making the car hesitate........your comment re. transfer case fluid will fit that profile but I guess the viscosity will need to be too low for it to really move.......

If you find the issue, pls post the answer/outcome, will be curious to see if is transfer case/.....

[ltemup4650]

ard and smassey321,

I thought I covered everything I've tried in the original post, but I failed to mention I tried doing what you suggested. Specifically, I unplugged the xfer case at the actuator and the issue remained. After unplugging it, I even removed the front driveshaft and took it for a drive which pretty much takes the transfer case out of the equation. I'm still highly suspicious of the trans pan. I had bought an aftermarket one. I'll probably buy a ZF one and see what happens. Losing suction makes the most sense as it would be a cause that would unlikely through a code.

[ltemup4650]

CLS70, unlike many (at least on other forums), If I resolve an issue, I always post the solution. It's the right thing to do.

[Purplefade]

You won't like it, but it may help... I had nearly the exact same thing happen to me with my ZF after I did a fluid change replacing the pan gasket and filter. I got everything back together with no issues at all, I mean breezie smooth for a ZF transmission (I did break one pan bolt that I had to replace, so I just replaced hem all... but that wasn't the trannies fault) but when I took it out on the road it "stuttered", it's been long enough ago now that I can't tell you if it was worse turning left or right, but it definitely stuttered.

I pulled the pan and found that the filter and pickup had come unseated.. not really sure how with its proximity to the bottom of the pan, but it did and upon inspection I found "ridges" in the pickup tube hole from the old o-ring. I took a 2000 grit piece of sand paper and wet it really well with trans fluid and "sanded" until I couldn't feel those "ridges" anymore - re-seated the pickup & filter, replaced the pan, refilled and test drove - problem gone, shifts like butter (OH MY GOD - not to jinx myself ).


Hate to say it, but you may have to pull the pan, just to be sure, it does sound fluid\pickup related.


Good luck!!