SMG Grinding After Track Session

[Da Jemster]

Thanks! This is what I suspect. Is the GPS more than just a sensor? Is there something mechanical inside the GPS that makes the sound?

sapote answered this exactly...

[eacmen]

Okay so bumping this thread.

I solved the noise that happens when car is stationary. It was air getting into the hydraulic system at the reservoir. The other SMG relocation thread was spot on in that regard.

However the gear grind still happens occasionally. Did the bleed and adapt several times. This last track day was able to capture it on video. When it does happen its always on the 5 to 4 downshift. Can happen when trans is hot or cold. And happens when driving the car like a grandma. Video here:

https://youtu.be/dD_nShxXSLE

Curious what you guys think. Bad synchro?

If you look on the dash the gear indicator goes from 5 to 12 to 4 to 12 to 4. This is logging the raw CAN messages on the SMG ARBID from the DME.

[eacmen]

Also looked at the data from when it happened:

[sapote]

However the gear grind still happens occasionally..
Curious what you guys think. Bad synchro?

Bad 4th synchro? I don't think so, as most of the time it should be 1st (or 2nd for our cars)
If there is no smg codes then I think the slave cylinder position encoder didn't report the correct value to the computer and so the computer did push the TOB far enough to completely disengage the clutch. So try to swap out the slave or its encoder.

[heinzboehmer]

Worn pivot pin would also cause something similar to what sapote is describing, but I would think that would cause grinding in all gears, all the time.

[Rich022]

Reading thru all this. First question, did you successfully run thru the INPA adaptations. Whereas the last screen of requires you to start the engine and drive the car ?
if that was successful —all of your SMG and clutch components are working properly.
2-grinding sounds like the infamous 4th gear synchro going out. That’s purely mechanical in your transmission and independent of SMG. You can minimize this by lifting off throttle before shifting into 4th gear and using mode 2, which allows for slower gear shifts.
I’ve been doing this for about a year now as there’s no fix. .

[eacmen]

Reading thru all this. First question, did you successfully run thru the INPA adaptations. Whereas the last screen of requires you to start the engine and drive the car ?
if that was successful —all of your SMG and clutch components are working properly.
2-grinding sounds like the infamous 4th gear synchro going out. That’s purely mechanical in your transmission and independent of SMG. You can minimize this by lifting off throttle before shifting into 4th gear and using mode 2, which allows for slower gear shifts.
I’ve been doing this for about a year now as there’s no fix. .

Yup! Did the full INPA procedure including the screen you showed. I actually do it once before each track weekend to make sure all is good.

If you look at the data I was off throttle when it happened. Any reason you can think of why it only happens downshifting into 4?

I was in mode S4. Havent tried S2.


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[George Hill]

I'm having trouble following the complete issue and I couldn't hear the noise in the video... BUT I will say that when we were running the SMG in the endurance car it was killing 4th gear and we usually heard an audible noise most drivers would call grinding when shifting into that gear. Team owner decided when ever that happened that I switch the transmissions, I'd do all the normal maintenance (new parts in BH and all the springs/pins/etc) and when I put it back together it was always fixed. Maybe there was some underlying issue but that is what we saw and that was the outcome with the work done. (We couldn't afford an attempt to fix if it didn't work and shot gunning a trans was the best option for the situation).

[Rich022]

Hi George,
Question --"When i put it back together it as always fixed". Do you mean you eliminated the 4th gear synchro grind by replacing the usual pins/springs ?

[sapote]

I'm having trouble following the complete issue and I couldn't hear the noise in the video... BUT I will say that when we were running the SMG in the endurance car it was killing 4th gear and we usually heard an audible noise most drivers would call grinding when shifting into that gear. Team owner decided when ever that happened that I switch the transmissions, I'd do all the normal maintenance (new parts in BH and all the springs/pins/etc) and when I put it back together it was always fixed. Maybe there was some underlying issue but that is what we saw and that was the outcome with the work done. (We couldn't afford an attempt to fix if it didn't work and shot gunning a trans was the best option for the situation).

Hi George,

Are you talking only SMG or including manual tranny? If only SMG then there is not much inside or outside the bellhousing to replace, but you seem to point to the gate selector 2 detent pins and springs/sleeves. Did you replace the detent balls/spring at the upper right rear for the R, 1/2, 3/4 shift rods? The 3/4 rod is the lower one on the right side of the box.

[sapote]

However the gear grind still happens occasionally. Did the bleed and adapt several times. This last track day was able to capture it on video. When it does happen its always on the 5 to 4 downshift. Can happen when trans is hot or cold. And happens when driving the car like a grandma. Video here:.

I can't tell the gear grinding noise in the video.
Have you removed and checked the 3/4th gear detent ball (old part) or pin (new part) with spring under the metal cover on the upper right rear of the box? See pic below. 3rd and 4th detent ball or pin is the lower hole. Do not pull things out of the other 2 holes in the middle of these 3 detent pins.

[George Hill]

Hi George,
Question --"When i put it back together it as always fixed". Do you mean you eliminated the 4th gear synchro grind by replacing the usual pins/springs ?

There seems to be some guessing as to what could be the issue or what could be the fix, I don't know for sure. I was trying to articulate (and not to well as I re-read) that on the endurance race car we consistently had issues with 4th gear. I have a couple theories but since it was a rental it was hard to actually test/implement those theories. So the team owner would always request we replace the transmission. Transmissions rarely were verified "good" before given to me and sometimes we used manual transmissions and swapped BHs. Whenever I swap or work on a clients 420g I have a punch list of parts I always replace. So once back together with the "new" transmission we always eliminated the grinding, at least "temporarily" and by temporarily I mean multiple race weekends which on a good weekend are 16-20hrs.

Hi George,

Are you talking only SMG or including manual tranny? If only SMG then there is not much inside or outside the bellhousing to replace, but you seem to point to the gate selector 2 detent pins and springs/sleeves. Did you replace the detent balls/spring at the upper right rear for the R, 1/2, 3/4 shift rods? The 3/4 rod is the lower one on the right side of the box.

Unless this is a job unrelated to the trans and I just have to pull it and reinstall, I always replace the TOB, TOB guide tube, fork and pivot pin inside the BH.

If its a SMG car then I replace everything in the SMG diagram:

https://www.realoem.com/bmw/enUS/showparts?id=BL93-USA-10-2002-E46-BMW-M3&diagId=23_0956

If its a high mileage manual or if I am converting a SMG to 6MT I replace/install everything in the manual diagram (except the R and 5/6th detent pins on manuals):

https://www.realoem.com/bmw/enUS/showparts?id=BL93-USA-10-2002-E46-BMW-M3&diagId=23_0887

I also replace and only install BMW selector rod joints.

[sapote]

Unless this is a job unrelated to the trans and I just have to pull it and reinstall, I always replace the TOB, TOB guide tube, fork and pivot pin inside the BH.

If its a SMG car then I replace everything in the SMG diagram:
https://www.realoem.com/bmw/enUS/sho...diagId=23_0956

If its a high mileage manual or if I am converting a SMG to 6MT I replace/install everything in the manual diagram (except the R and 5/6th detent pins on manuals):
https://www.realoem.com/bmw/enUS/sho...diagId=23_0887

I also replace and only install BMW selector rod joints.

This makes sense. For SMG, the first part kit has all the shift rods detent pins and springs for R, 1/2, 3/4 , and the ball/spring for 5th/6th (I don't know why RealOEM updated the detent balls to pins -- some call them sleeves -- for R, 1/2, 3/4 shift rods, but didn't update the 5th/6th detent ball to pin).
Thanks.

[eacmen]

Wow so it seems from George's post that this just seems to be an inevitable issue for heavily tracked SMG?

I have not yet dropped the trans to investigate this issue. At least it happens when the trans is mostly unloaded (slow speed, off throttle). It sounds much worse in the car than you can hear in the video.

For those that said they couldn't hear it, it starts at second 6.

Was mostly hoping someone would hear it and know if it was a synchro or something else. Just trying to diag as much as possible before dropping it.

The other weird issue is that right before it happens the voltage drops off. Its still above 13v. The RPM also drops (so alt is not providing as much voltage?).

[Rich022]

You can't mistake a synchro grind - I saw that that voltage drop too in your data. odd - does it occur every time shifting into 4th? long shot is GPS doing somethin hencky and not fully engaging gears? idk.
My grind only occurs under load and rarely when shifting at low rpms/no load. --hence I can let rpms drop by lifting (a '1' count) then successfully shift into 4th.

Most folks investigate the springs and sometimes indeed they are broken -Part 6 and 9 in the diagram. BMW had an update to stronger springs. keep us updated on your findings.