91quattro

I’ve got a shudder that started showing up a few weeks ago. In Drive, when I am coming to a stop, just as the car shifts from 2nd into 1st, there is a half-second shudder. Doesn't happen with any other gear changes. I can feel it in the steering wheel and pedals, and I can hear it coming from the front of the car. I thought it might be the AC/compressor, but it happens even when the AC is turned off...so it seems to be the trans. It doesn’t always happen, but tends to be there if the car is cold, or when coming to a stop on a slight downhill slope versus an uphill slope. Once the car is warmed up, it happens maybe 20-25% of the time. It seems like it happens more when braking to a quicker stop, versus a slow roll to a stop. It doesn’t seem to happen at all in Sport mode. I have never had this shudder before, in the 8 years I’ve owned the car.

So what has changed? Well, I have had the classic transmission hoot for years, and so in December I drained and flushed the trans (for the first time). Did a double flush with LG6, new gasket and pan filter. Car has about 103K miles. After each flush, everything was fine. It eliminated the hoot I had between 3rd and 4th and generally everything was nice and smooth. Then several weeks later, the shudder shows up. Trans has original firmware, it’s an HHV with 0010 FW. I didn’t do an adaptation drive after the drain/flush, because it didn’t seem to need it, but now I wonder if that might be worthwhile.

What else? I have also had valve cover gaskets replaced, and the indie mechanic found the front suspension bolts a little loose, so tightened them – all of which seems unrelated, but you never know. Otherwise, nothing has changed.

Obviously I’m wondering how serious this is, and if I should be concerned. It just seems odd that it has never happened before, and now it's there. The car drives fine and the trans shifts fine. Any thoughts or ideas are appreciated.

MP4.2+6.0

1. Check fluid level again. Make sure you don't have a leak. That's the easiest.

2. After that, some chance it is the seal between valve body (Mechatronics) and main transmission case. The filter hangs off the valve body, so you saw it right in front of you when you did the pan drop and filter. I have posted on a lot before--did the work, pics, etc. Issue also seen with heavier BMWs of era using similar (non AWD) ZF tranny. Can search for those posts. I even commented on/referenced/linked those again in a couple of tranny threads in last few weeks. That can't be diagnosed by any known/for sure method AFAIK. Mine was shift miss in 5-6, but BMW ones I think have been in low gears like you mention.

91quattro

OK, I checked and no leak. Garage floor is completely dry. I have not had a chance to check fluid level yet.

After paying more attention I have noticed something else. When I am coming to a stop, I hear the AC compressor running, and as I reach a full stop, I hear a relay click in the driver's footwell, the compressor shuts off and the shudder happens. It sounds like the compressor is keeping the engine RPM higher until the relay cuts it off and RPMS go to idle speed - and the shudder occurs. I think that's why I initially thought it was related to the AC compressor. In fact I hear that relay clicking on and off quite a bit - is that normal?

MP4.2+6.0

Can't diagnose that directly, but a possible theory would be the AC compressor is engaging more and causing a sudden big power suck when motor is idling w/ little torque. But, the compressor is not the typical old school solenoid on off that engages a belt clutch. Instead it has a duty cycle--not single "on/off" type concept while running. Thus not clear what you are hearing, though could be fans cycling with compressor.

Before it gets too hot there...try putting AC in Econ mode via the control selections you then see as a choice on the MMI screen. Drive around. Now see if it does the shudder rolling to a stop or not. If no shudder now, you have an answer it is somewhere with AC. Logical next thing there would be to get system refrigerant checked/recharged; needs shop equipment for that to weigh properly. Resist stuff in can that may overcharge system and create issues. If it shudders and AC definitely in Econ mode, you can basically eliminate that theory though you would still want to isolate reasons for clicking, which could still be a separate AC charge or other issue.

91quattro

Amazing,. I never knew MMI displayed AC information until now! The hidden menu did not have Air Conditioning checked. Just put it in Econ for the first time since I've had the car - 9 years. I'll go for a drive shortly and see how it behaves.

MP4.2+6.0

It should display it, Hidden mode or not. You just have to select via HVAC control panel and have the info pop up on the MMI screen. What is not so intuitive is sticking with the HVAC controls to do things while it is displayed on the MMI screen--instead of switching to the MMI wheel and such.

91quattro

Got it, it was not displaying on MMI until I selected "Air Condition" in the hidden menu, but all is good now.

So I went for a drive and tried a few things... in Econ mode, the shudder is still there. In Econ and with the whole Ventilation system turned to Off, it is still there. The sound I was hearing (like a low growl), that I thought was the AC compressor, is also still there. So it must not be the compressor making that noise as I come to a stop. But I also noticed, twice, a shudder that seemed to be from 4th to 3rd as I slowed down. And, the shudder is always accompanied by the relay clicking and the "low growl" noise stopping. So now I'm not sure what that growl is, but it seems more than likely it's the tranny...I don't know enough about how transmissions work.

So MP4.2+6.0, back to your original diagnosis - would low trans fluid cause these symptoms? I had an indie shop change the fluid so I never did see the Mechatronics unit or valve body. If fluid is OK, how involved is it to change that seal?

MP4.2+6.0

In general low fluid can cause shifting issues from a variety of posts specific to D3, plus general common sense for trannies generally.

Suggestions:

1. looking back to your original post, it says you didn't do a transmission adaptation drive post fluid change. That is certainly worth doing at this point as next step. Post the work I did on mine when I finally did it full on down to the seal, it went from mediocre on stat up and initiation of adaptation, to like new crisp 30 minutes later...and ever since. Fluid change only at earlier step, it helped some, but issues recurred.

2. Next up, I would check fluid level, or get shop to do it. Because car has to be level, it is difficult to do in many home garages w/out a lift. I can actually do it with ramps and car pointed nose down on my driveway that has the right upslope, but unusual. Assuming shop, remember needs to be checked at approx. 40C---not cold but not full operating temp either---so likely need to drop off for them to have it long enough to cool some. If they don't have VCDS BTW, I found the measurement I got with an IR type temp gun aimed at pan was essentially identical to the VDCS sensor read. IR method is more practical when under car deciding when to open oil plug, check and top up if needed.

3. After that, it is imprecise for further diagnostics and more invasive. Seal would be next most likely. You then get into opening pan and removing filter, so it is basically another round of a full fluid change cost wise. Given you did it recently, I would just do single cycle this time if you end up here. New solenoid set for the valve body (what regulates the shifts) would be another step from there. A tranny type shop should of course be comfortable doing the basic valve body removal, esp. one that works on ZF's. A general mechanic who is fine dropping pan and filter may feel over his head though, for legit reasons. It is pretty straight forward w/ experience, but related linkage removal and reinstall needs to be done by the book and/or someone who knows the ZF six speed. Having done the 5 speed ZF too, they are not the same at all on the linkage related tie the 6 speed has. I did it under the car with the printed instructions basically in my oily hands. Otherwise it is basically held in by a whole bunch of screws. There is a general removal order and you (mechanic) need the diagram of which ones you remove and which stay. If you get into the valve body solenoids, that requires disassembly of fragile parts. Body has to be treated carefully, but all that is being done is to set it aside gently for 5 minutes to pull old seal, clean up surfaces and then start reassembly. Again I did it and all went fine, but professionally it may be only a ZF trans. shop would be comfortable at that level.

Next step, adaptation and keep fingers crossed.

91quattro

Thanks for all the great information. I plan to do the adaptation drive in the next couple of days. If that doesn't resolve, I'll get the fluid level checked and go from there.

Adaptation drive - I assume this should be on a flat road? Kind of a challenge to find one that lets me basically do a slow acceleration to 50 followed by a coast to a stop...4 times...

MP4.2+6.0

Yes. I had the same issue. The move shifter to different positions part is easy, but I had to think a while in built up SF Bay Area where I could do it without driving an hour somewhere. Finally thought of a street (classified as a local highway) ten minutes away where lights are pretty far apart. Went out w/ my laptop to trigger start about 11 at night for light traffic and better shot. Figured it might take a few tries, but luck was with me with prevailing greens. I got both the slow speed up and coast down, at least to last 5 or 10 mph when I had to stop or get out of way. I would just linger on shoulder until I saw a nice long opening to at least start the slow roll going.