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Transmission Drain Plug

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Anonymous
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Every time I loosen a drain plug from a Mercedes transmission oil pan or torque converter, I have a sickening fear of camming-out the 5mm female hex. I haven't had it happen yet, but did have a case where the hex bit turned about 20 or 25 degrees before the plug loosened. The other day, a local indie had a drain plug cam-out completely. He had to weld a nut to the plug to remove it. Fortunately, it was the oil pan plug, so he could do the welding off the car. The Mercedes transmission drain plug is a DIN 908 with M10 x 1mm thread.

Maryland Metrics carries a DIN 910 plug. It is same dimensions as the DIN 908 plug, except that it has a hex head which is 6mm high and 10mm across wrenching flats. I am thinking seriously at installing DIN 910 plugs when I service the transmission fluid and filter in my 123 body. I plan to put a lump of modeling clay on the torque converter plug and turn the engine one revolution to be sure there is clearance for the extra 6mm plug height. I am also considering using the DIN 910 plugs when servicing customer transmissions.

What are the pros and cons of using the DIN 910 plug instead of the DIN 908 plug? Have any of our forum members made this substitution? Comments? Precautions to observe? What is a good method for removing cammed-out drain plugs that doesn't involve welding?

The DIN 910 plugs are $ 1.51 each. Maryland Metrics also has 10mm ID by 14mm OD by 1mm thick seal rings for 12 cents each.

If you want to see a dimensional drawing of the DIN 910 plug, go to http://www.wiberger.se/templates/din910.htm The M10 x 1 plug is the first item in the table. You can look at the DIN 908 plug by changing the address from 910 to 908 and resending. Thanks.

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Alex's picture
Long Island City, NY
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2004 Sprinter
2004 CL500
2004 C320
1981 300TD

Jim,

Other than the difference in size, in what way is the DIN 910 plug different than the DIN 908, that would prevent it from camming out the female hex?

Do you mean that the extra 1mm of grab height in the wrenching flats will prevent camming out?

Wouldn't a new hex wrench with really sharp edges do as well?

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Alex Rosner
Member, NYC-Long Island Section
Member, MBCA Technology Committee

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Try using a 1/4 drive ratchet with a 5mm allen and when the plug is seated, turn an additional 1/8th of a turn. Use the correct copper crush washers. I've noticed that they come in two different widths. The narrow one always leaks. Snap On/Blue point makes left hand twist rounded off bolt removers. They are the cat's *ss. ;)

Jim Grillot (not verified)
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Alex, the 908 plug has a six-sided hole with 5mm across flats in it. You stick an Allen wrench or hex bit in the hole and turn. The 910 has a male hex which is 6mm high and takes a 10mm wrench or socket to turn. Take a look at the Wilberger drawings and it will be obvious.

Sur5er, I use new seal rings and torque to 14 Newton-meters. The problem is what the last guy or gal who tightened the plug did. If s/he tightened the heck out of the plug, it could be bad news for the next person who has to remove the plug. FWIW, the 14 x 10 x 1 seal ring is a DIN 7603A, 14x10x1.

I have another theory on camming-out. It is that sloppy, slightly undersize hex bit sockets are more likely to cam out the drain plug hex. I have a Hazet 5mm hex bit socket on order. I am hoping that Hazet pays more attention to the dimensions across the hex bit flats than do the American tool manufacturers.

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Alex's picture
Long Island City, NY
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Joined: January 12th, 2004

Posts:
3601

Vehicles
2004 Sprinter
2004 CL500
2004 C320
1981 300TD

Jim,

Thanks for clarifying. I now see your point and yours does seem like a worthwhile solution.

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Alex Rosner
Member, NYC-Long Island Section
Member, MBCA Technology Committee

Jim Grillot (not verified)
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The DIN 910 hex head drain plugs arrived from Maryland Metrics yesterday. They look good. I am considering reducing the head height by 2mm to 4mm. I don't think the head really needs to be 6 mm high. Cost with shipping was $ 2.21 ea.

The DIN 7603A seal rings in 10 x 16 x 1 size look like they will be superior to the 10 x 14 x 1 rings from Mercedes. Cost with shipping was $ 0.19 ea.

I plan to put a piece of modeling clay on the torque converter drain plug and rotate the engine one turn to make sure there is clearance for the hex head on the drain plug.

I also bought a 5mm Hazet hex bit socket. It is 0.0005 inch larger across the flats than the american-made hex bit I have been using. This larger size may help prevent camming-out.

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