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Discussion Starter · #1 · (Edited)
Apparently the right-rear wheel's speed sensor is used by the transmission's (and transfer case's?) computer, so if the sensor gets wacky readings it makes sense that the computer would make the transmission act strangely.

I just cleaned the RR sensor and its reluctor ring today on my X3.1.2 #1 in an attempt to reduce the intermittent surge-shifting of its automatic transmission. I've only done a short test drive so far and will report back in about a week if there's a noticeable change in the driveablility, for better or worse.

All work at your own risk. Be safe! Gravity is working against you, and brake dust is harmful.

Parts:
None (hopefully)! However make sure you have the OEM jack-pads and that they are preinstalled under the rockers (many pad sellers on eBay).

Tools:
N95+ dust mask (possible asbestos, etc. brake dust hazzard)
Floor jack, two jack stands, and wheel chocks (or a proper mechanic's lift)
Metric hexkey wrenches, or sockets (only one small size needed = 5 or 6 mm?)
Droplight or similar
Vacuum with flat-nozzle hose attachment
Large screwdriver or other pry bar
Small/thin/long flat screwdriver
Toothbrush
Small wire brush (I used a brass, toothbrush-like one)
Air gun/socket, or tire cross
Sturdy, flat floor

Time:
About an hour and a half for the first one; likely half that for future jobs

The procedure I used:

Installed wheel chocks on a front tire

Released the parking brake

Jacked up the rear of car, via the center of the rear differential, until the back tires were off the floor by about three inches

Installed the jack stands under the two rear OEM jack pads

Lowered the car until it just-contacted the stands; checked the stands for centering, etc. When OK/safe, lowered jack fully. (I like to raise the jack again to make slight contact, as an added safety measure.)

Donned the mask.

Removed the right-rear wheel, and put it under the right-rocker for added last-resort safety (working under a jacked-up vehicle is inherently dangerous ...)

Reinstalled the five lug bolts, by hand, halfway

The black speed sensor is on the top/forward side of the hub, just behind the brake disc. Removed the sensor's hexkey screw. Used the small, flat screwdriver to pry the sensor up slightly, a little at a time from its top and bottom sides of its flange. My sensor was slightly stuck due to rust flakes.

With the speed sensor removed, cleaned it quickly and inspected it for wear-away of the tip. Mine was very dirty/rust-covered, but otherwise fine. I cleaned it and its mounting hole well to remove the rust to make sure it would fully seat when reinstalled.

Put the turned-on drop light under the hub assembly, a bit toward the front. Looked down through the sensor's hole and repositioned the light until I had a good view of the reluctor ring inside.

Used the large screwdriver as a lever between a couple of opposite lugbolts to turn the hub bit by bit. Not super easy on mine, and the other rear wheel turned in the same direction (why it had to be raised too so that it could turn freely). If the RR wheel doesn't turn for you, make sure that you have fully released the parking brake (doh!).

Judged the condition of the reluctor wheel. If yours is really awful, you may want to put it back together now and order a new reluctor ring (eBay, a UK seller?). Mine wasn't too bad looking.

Installed the vacuum's nozzle from inside to under the hub, and turned on the vac to suck-out the dust, etc. while working.

From behind and inside the hub I cleaned the ring with the toothbrush, via scrubing down on the top of the reluctor ring, then turning the hub a little via the large screwdriver and the lug bolts, then scrubbing again, etc., until all the ring was done twice.

Vacuum turned off.

Then, from above/front, through the sensor hole, I used the long/thin/flat screwdriver to scrape-out the little rectangular gaps in the ring, one by one, turning the hub a very little each time with the large screwdriver. Most of my ring's gaps were fairly clean, but ten or so gaps had crud in them. And several were full of tough-to-remove rust-crud. Via those I could see how the magnetic pulse/pick-up sensor, and thus the trans' computer, might have been confused.

I scraped all the gaps again just to make sure they were all cleared out. Then lightly scraped the ring's raised surfaces with the little screwdriver to make sure there were no protusions. The ring's top was then all somewhat shiny looking, and another toothbrushing, with the vacuum turned on again, made sure all was relatively clean.

Removed the vac, reinstalled the sensor and the wheel, and lowered the vehicle. On the ~1/2 mile test drive it did well, although time will tell if the transmission's behavior is actually better as I drive in different situations.

My X3.1.2 #2 shifts better than this #1 does/did, but now I want to clean its RR sensor and ring too! I hear there's also such on the LF hub too, however that it's mainly for the ABS???
 

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Discussion Starter · #2 ·
Count Dracula speaks!

Here's the YouTube video that inspired me in this effort:

https://www.youtube.com/watch?v=ldTNuilNbJ0

Also kudos to those here who mentioned the possible need for this cleaning/repair work.
 

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BMWaufKS,

That was an awesome write up and something that I will be doing as preventive maintenance. The video was great as well. My question to you is the video shows using air to blow dust out, but did the vacuum get the particles out that you cleaned off? Would using air and cause any issues? I may end up doing both, LOL. Thanks for your time and thanks for the post.
 

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Discussion Starter · #4 ·
BMWaufKS,

Would using air and cause any issues?
NEVER use compressed air with brake-dust, unless you don't want to live as long as possible.

Using a HEPA filter on the vac would be good.

Probably few pads/shoes still have asbestos in at least the U.S., but the modern fine, abrasive replacement particles must be not good for our lungs either.
 

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Discussion Starter · #5 ·
Just went for a ~7 mile drive of mixed highway and city driving. So far, the surging seems gone! :) The super kick-down shift going up a slight hill slowly is still there, though.

One other possible change is that when slowing for a full stop, it used to hang on to the higher gear(s) too long -- it seemed to downshift better today.

However, it's still too early for a conclusion as to the effect of this maintenance work.
 

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BMWaufKS,

Luckily I have some actual gas masks that I used when we had our business, so I will not be breathing any particles as the mask are so much better than the dust mask. Yes, the filters cost quite a bit more, but I have a stock pile from when we closed it down. May I ask how many miles you have on yours as I am considering replacing the sensor? As for the reluctor ring, I will look mine over and if needed, then take on that task as it looks to be a lengthy process.

Please keep us posted as to how yours is doing. I have not had any of the symptoms you have mentioned, but figure that I will just do it as preventive maintenance.
 

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Discussion Starter · #7 ·
Somewhere around 95K miles on #1. However the undercarriage is dirtier than #2's which has about 146K (and looks nearly pristine, at least from below).
 

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BMWauf KS,

Thanks for the information. I noticed you have dash cams in both, may I ask what you have and how you like them? We are looking at one that we can put a 128GB micro sd in and that will cover us for a lot of recording. Again, thanks for your assistance and if anyone else has opinions they want to share, then please do.
 

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Discussion Starter · #9 ·
Black Box G1W. Wait for no more than US$35 on eBay, from China. Plus a 32GB Class 4 (_not_ 10) card, female lighter adapter, and a 5 amp Add-A-Fuse. The G1W is a PITA to set up/debug, but once running is fine.
 

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Discussion Starter · #11 ·
Conclusion: Yes, this RR sensor and reluctor maintenance has incrementally improved my X3.1.2 #1 automatic transmission's behavior. Not perfect, but much of the very low speed surging is gone. This is both on acceleration and on braking. The typical other shifting-gremlins still need to be solved, though. Next, when I get around to it, is likely for me to tool-up for and learn about the DIS, INPA, etc. adjustments to the computer(s). There's a whole, separate forum on here just for that!
 

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Cannot believe that cleaning the sensor hole off all the rust and brake dust fixed the RR air gap and transmission warning light issue. Still replaced the sensor but pretty sure I didn't have to If I only cleaned it out with a dremel prior. It maybe a temporary fix but I will take it than having to replace the drive shaft.
 

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Discussion Starter · #13 ·
Glad it helped! Did you clean and inspect the reluctor ring too?
 

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Discussion Starter · #15 ·
Hmmm ... I don't remember seeing a coating on either of mine. Was the "rubber" very loose, like maybe it was shavings off the old sensor?
 

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I think this procedure is on my horizon in the next couple of days. My 08 threw the TPS, 4x4, ABS and Hand Brake lights, along with airbag earlier today. Drives perfectly normally, no issues with shifting mind you its a 6 speed manual. ISTA shows DSC, Wheel Speed Supply, rear right. 05E40.

Being in the rust belt, I may need a new reluctor rings which is not the end of the world as I'd rather do that then buy a new rear shaft as they are very pricey.
 

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I tried this and the success was short lived. My issue was rust under the reluctor ring caused it to go out of round and create an inconsistent gap between it and the speed sensor. A few washers made from a beer can helped but in the end I bought a new CV axle to permanently fix the problem About $200 on FCP Euro.
 

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I tried this and the success was short lived. My issue was rust under the reluctor ring caused it to go out of round and create an inconsistent gap between it and the speed sensor. A few washers made from a beer can helped but in the end I bought a new CV axle to permanently fix the problem About $200 on FCP Euro.
$200 for the rear axle? Where do you see this on FCP? You must be talking front?
 
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