I finally had to remove fuse block 1 as part of replacing my ignition switch (which was a huge ordeal I hope to find time to post on) and I found that the reason this bolt invariable seizes is that the design of the retaining bolt for fuse block one is flawed. The flaw and the fix are below:
Just as described by others in this post, I was unable to remove the bolt to FB1, so I tried the spinning very fast in the electric drill approach – still no luck. The method I used to remove the nut was to turn the steering wheel upside down and lever it out with a screwdriver:
Here is the design flaw – the bolt is not threaded to the corner of the shoulder:
The nut does not have any chamfer. So the threads are mangled when the bolt is installed at the factory and this causes the joint to bind up :
If the nut was machined into a metal part, it would still be a terrible design, but you could probably apply enough torque to remove it. However since it is simply pressed (not molded) into plastic it spins if enough torque is applied
The fix was to remove the bottom two to three threads with a step drill to provide the necessary thread relief and clean everything up with a M5x0.8 tap and die:
I was going to 5 minute epoxy the nut back in place, but there was plenty of friction to keep the nut in place and keep it from spinning. Everything is back together and working properly now, despite the Mercedes engineer’s poor design from the factory.
And now for a rant: Providing proper thread engagement for a fastener is mechanical engineering 101. A summer intern might make this error, but every mechanical engineer that has ever designed hardware should understand how to design a bolted connection – this should never have gone into production. As you can see from the pictures, my bolt had no corrosion and this is not a function of age. If this came from the factory yesterday it would still be seized. The proper design fix is to add an undercut to the base of the bolt or to chamfer the corner of the nut, but these add an extra machining step and increase the part cost, which is presumably why it was not done (I cannot believe it was ignorance). I give the Mercedes engineers an F on this part.
Just as described by others in this post, I was unable to remove the bolt to FB1, so I tried the spinning very fast in the electric drill approach – still no luck. The method I used to remove the nut was to turn the steering wheel upside down and lever it out with a screwdriver:
Here is the design flaw – the bolt is not threaded to the corner of the shoulder:
The nut does not have any chamfer. So the threads are mangled when the bolt is installed at the factory and this causes the joint to bind up :
If the nut was machined into a metal part, it would still be a terrible design, but you could probably apply enough torque to remove it. However since it is simply pressed (not molded) into plastic it spins if enough torque is appliedThe fix was to remove the bottom two to three threads with a step drill to provide the necessary thread relief and clean everything up with a M5x0.8 tap and die:
I was going to 5 minute epoxy the nut back in place, but there was plenty of friction to keep the nut in place and keep it from spinning. Everything is back together and working properly now, despite the Mercedes engineer’s poor design from the factory.
And now for a rant: Providing proper thread engagement for a fastener is mechanical engineering 101. A summer intern might make this error, but every mechanical engineer that has ever designed hardware should understand how to design a bolted connection – this should never have gone into production. As you can see from the pictures, my bolt had no corrosion and this is not a function of age. If this came from the factory yesterday it would still be seized. The proper design fix is to add an undercut to the base of the bolt or to chamfer the corner of the nut, but these add an extra machining step and increase the part cost, which is presumably why it was not done (I cannot believe it was ignorance). I give the Mercedes engineers an F on this part.
