M12 Aluminum bolt found in my undertray... - Mercedes Benz SLK Forum

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#1 Old 07-14-2019
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M12 Aluminum bolt found in my undertray...

So, during an oil change, a rather large M12 Aluminum bolt with a sheared end was in my undertray. Threaded throughout. E20 Torx head. Length is 67mm to the shear point so probably a 75+mm length. Visual search has been unproductive in finding where it came from so I can drill and tap it out and replace it. Have been trying to use the web to figure out where it goes (has to be a significant component, right?) without much success. Car has no symptoms (vibration, leaks, etc).

Closest in appearance is this: https://www.amazon.com/Mercedes-Torx.../dp/B076GP8CHV

But those are rear subframe...no way to migrate to the undertray. I checked mine anyway...they are all intact.

Really puzzled here. Any help appreciated.
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#2 Old 07-14-2019
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Hi,

Has the Car had any front suspension work like wishbones, steering box etc ??

Could have been sheared, bashed out with a punch and then fallen into the tray, and new bolt used to replace it ??

I'd be having a good looky see at everything safety critical if I were you

HTH, Cheers Dave
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#3 Old 07-14-2019
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Originally Posted by Dave2302 View Post
Hi,

Has the Car had any front suspension work like wishbones, steering box etc ??

Could have been sheared, bashed out with a punch and then fallen into the tray, and new bolt used to replace it ??

I'd be having a good looky see at everything safety critical if I were you

HTH, Cheers Dave
Thx for the response. I did the front control arms myself about 15K ago. But that is all intact. I have scoured the engine bay top to bottom several times now looking for a "gap" in a bolt location...I know I am missing it but it certainly isn't obvious. I guess I need to get out the mirror and look in the places I can't see without one. The weird thing is that I can't find many other M12 bolts in the online diagrams or the WIS software tool I have (hard to search for a bolt size in that BTW. I found a mention of one for the transmission to engine but cannot find a diagram to show me which one is an M12 and all the ones I can see are smaller (M10 per the diagrams and WIS) and intact.
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#4 Old 07-14-2019
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Dave is one of our go to guys.

I'll add the others on the off chance.

@Mn car guy
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#5 Old 07-14-2019
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Originally Posted by Avel Du View Post
Dave is one of our go to guys.

I'll add the others on the off chance.

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Thx, much! This forum has been key to my ability to keep this car in good shape.
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#6 Old 07-14-2019
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That's a huge bolt - I'm guessing tranny to engine too. I'd sure want to know too.
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#7 Old 07-14-2019
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Well, I used a mirror and bright lights...I have ensured all bolts are in place for the areas that could fall in the underbelly tray. And none were a size that matched what I found nor was there an empty hole that matched the M12 size. I checked:

- transmission to engine bolts (this includes starter bolts)

- P/S pump bolts

- Alternator bolts

- A/C compressor bolts

- Engine Mount bolts

- Suspension arm bolts

- steering knuckle bolts

- Any other bolt or hole I could see from underneath or on top...

No joy. This is pretty annoying honestly, but I guess I will just drive it until I get some kind of symptom. Thanks for those who posted ideas. If this was some easter egg stuck into a body panel by a disgruntled German Mercedes employee who is now long retired, all I can say is...well done ya XXXXXX
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#8 Old 07-15-2019
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Looks to me like the one-time-use bolts used to affix the tranny pan to the transmission. They are cast aluminum and torqued to yield. Perhaps at the last transmission service one broke, was fished out and set aside instead of discarded.

tn
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There aren't many M12 bolts on the car...

picture? general side/location of discovery?
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#10 Old 07-15-2019
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Originally Posted by Thomas Nelson View Post
Looks to me like the one-time-use bolts used to affix the tranny pan to the transmission. They are cast aluminum and torqued to yield. Perhaps at the last transmission service one broke, was fished out and set aside instead of discarded.

tn
The bolts for the transmission pan are much smaller.

Bolt pic

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#11 Old 07-16-2019
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Hi,

Purely to avoid grief for others and absolutely no offence intended ....................

Transmission Pan Bolts are definitely not TTY !!

8 Nm is the Torque figure

HTH, Dave
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#12 Old 07-16-2019
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TTY Torque to yield.
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#13 Old 07-16-2019
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go off-piste

that looks a bit like a cylinder head bolt to me. he said, never actually having seen one. the rocker covers are held on by similar, but i don't think they are M12.


NOT a cylinder head bolt, did some googling. They have a smooth section near the top, and are female torx drive. Ho-hum, back in my box.
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Last edited by Elmer Fudd; 4 Weeks Ago at 10:16 AM.
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#14 Old 4 Weeks Ago
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Intake manifold?
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Quote:
Originally Posted by Elmer Fudd View Post
that looks a bit like a cylinder head bolt to me. he said, never actually having seen one. .
Literally the first thing I thought due to the thick flange. Except a head bolt would not be a male torx.

have we looked at a drivehaft bolt? for the donuts?
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#16 Old 3 Weeks Ago
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Originally Posted by Turdo2 View Post
Quote:
Originally Posted by Elmer Fudd View Post
that looks a bit like a cylinder head bolt to me. he said, never actually having seen one. .
Literally the first thing I thought due to the thick flange. Except a head bolt would not be a male torx.

have we looked at a drivehaft bolt? for the donuts?
No path for those to fall into the tray. Tray doesn't even extend to the end of the transmission.
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