I had to replace the trunk lid on my 300SEL after some rear end damage, so after some searching I found a pristine replacement at the local pic-a-part in the same factory black color. The issue is that the new lid is aluminum because it came from a 300SD, so it literally flies open because the spring tension is all wrong.

I suppose I could go back and buy the springs and/or hinges, but perhaps someone here knows a way to adjust the tension of my existing springs? I haven't pulled the hinges off so I'm not quite sure what I'm dealing with yet.

After realizing that removing the trunk lid hinge/spring mechanisms requires removal of the rear deck material inside the car, I decided to cut the existing springs down with the hinges still in place.

I removed the trunk lid and took an angle grinder to the spring on the passenger side, mangling three coils in the process so that they were now separate rings stacked on each other. Comparing this hinge's new action with the driver's side revealed a noticeably lighter resistance. I did the same to the driver's side and put the lid back on to find things much improved, probably 50% better than before, but still too stiff.

So now if you get hit in the chin by the flying trunk lid while sticking your tongue out at your wife/lover/whomever, you likely won't lose your whole tongue, but it still won't feel none too good. I think I'll cut a couple more rings on each side.