CL203 Rear number plate bolt problem fix

[350_Coupe]

ok, the simple task of changing the rear number plate on my 203 Coupe caused me more of a headache than i expected, so figured i'd post the fix here, in the hope it helps someone else in the future.

Originally, before i purchased my car, it was on private plates, and the garage that swapped them back used some nasty cheap steel screws to refit the original plates, recently the rear plate has been looking a little tired and scruffy, and was de-laminating around the fixings, and one was missing, i was also noticing some water/corrosion marks appearing from behind the plate, so i figured time to order up a new plate and see what was going on.

I used number1plates.com and ordered up a rear plate, with my car model printed below the registration, a black section to the side with "Eng" and the english flag, registration in Hi-Line text, cost was reasonable, the required proof was just driving license and v5 photo, and was pretty painless and didn't slow the job down any.

Plates arrives nice and quickly - notice i said "plates".... ordered and paid for only the rear, but they sent both happy with that, but that's where the good fortune stops !!


First thing i did was to look at the original plate closely, and saw that one of the screws was sheared off, great...... tried to remove the other lower screw, on the opposite side, only for that to simply snap off at the head after very little pressure was applied, great


As i said, it looks like after the private plates were removed, the screws fitted were cheap horrible steel ones, with no protective coating, so they had simply rotted

So that makes it both lower fixings out of action, luckily i was able to remove the top ones without too much trouble. At this point i realised this was not going to be a simple/easy/fast fix.

here's the problem fixings (after i cleaned the snapped screws and socket face back a little)



the 3rd image above shows how the fixing socket should look


These "sockets" are aluminium, and are used because the rear hatch is fibreglass in that area (pictures from inside hatch below) so they use these rivet style threaded sockets, and by using steel screws, it had caused dissimilar metal corrosion, and not only caused the screws to rot and seize, but also to trash the aluminium surface too, causing the marks i was seeing below the number plate.
To try and remove these broken screws was likely going to cause more damage, drilling them out or trying ezy-outs was just not going to work.





At this point it became obvious that the original fixing method was out of the picture so to speak, for the lower fixings at least, and i had to find another solution.

The answer, those plastic number plate surrounds you see on ebay all the time and something called "Well Nuts" (x4).......



the well nuts are basically rubber top hat shaped items which have a brass threaded insert inside them, and come with a brass machine threaded screw, the ones i got required about an 8mm hole drilling, and work like this....




Now to solve the fixing to the car issue, firstly i decided that i wanted the mounting frame to be closer to the car than they would be if fitted to/on the original aluminium stand offs, so i made the frame fit around those by drilling matching holes in their locations, so they became locating pegs for the frame. (easier if you have a pillar drill you can use) here you can see 3 of the enlarged holes, i still had the lower left one to do when i took these pictures.




next, fit them to the car and mark where the new mounting holes will be for the Well Nuts, using masking tape to protect the paintwork when drilling (after drilling i used a small amount of black paint to coat the insides of the holes to seal the fibreglass)




Once the holes were drilled and the edges sealed with the paint, i also painted the original aluminium sockets to try and stop any further corrosion water marks from appearing, and then pushed the well nuts into position....




Finally i now have four good mounting points, and can attach the frame



and from the inside, the well nuts look like this before/after the frame is fastened into place





Rear number plate now looks a lot better - only thing to note, is that on the plates i bought, the positioning of the flag and Eng text is not good when it comes to mounting the front plate, the flag is too high and the text too low to avoid hitting them with the mounting screws!




Now i just need to find some LED bulbs to illuminate it, that work without triggering the bulb out warning, and don't break within 6 months! i did buy some replacement fixtures, that are self contained and canbus compliant, which i was hoping would be a direct replacement for the ones i have, but, it turns out the ones i got only fit the saloon/estate, because the coupes fittings are shaped different unfortunately.... so i now have those to sell!

 

[optimusprime]

Good post . My problem was when i put the screw driver in to remove them .Like yours it broke off .Next sillly step was to try and drill the old screw out .The drill bit i used ,it to snaped off .So i have three of the right type and one i made up of nylon that i pushed in the hole enough to look ok. But the nuts are a special part from mercedes . I have picked a few up in a lot i won on ebay. You need a special tool to fix them in .Would not be so bad if you could get to the rear to fix on a nut. But the gap is so small at the back its impossible to get a nut on there. Good post.

 

[350_Coupe]

yeah, those OEM parts are designed for machine fitting, i don't even know if you can buy the tool to fit them my hand/manually you did well to actually find the parts i think. Only way i know of to do those my hand/manually is to have a 2 part tool, like a drift and swauge affair, where you mount one part in a vice, place the components over and belt it with a hammer till it crimps them together, seriously hard work when your talking about the rear hatch, and hugely reduced access !!

As you said, space is seriously limited back there, but it could be worse, because they are spaced for US license plates, so are closer to the middle, and wider section of the rear hatch, closer to where the access holes are.

For your, i'd be tempted to get a pair of very sharp, preferably brand new side snips, and try and snip through the aluminum rear tube section, allowing you to then get a small dremel in there to grind off the crimped section, and thus remove the whole socket affair, being careful of course as the fibreglass will be easily cut into, when cutting through, rotate the cutters around the tube, like the motion used with a a pipe-cutter for plumbing pipes.

From there, then try and find well nuts like mine, that will fit the size of hole you are left with, or hopefully, slightly larger, then you can gently file the hole to suit.

 

[Will]

Would it not have been possible to drill out the old screw remains and re-tap the fitting?

Or to knock the old fittings out and replace them? Then use stainless scews

This has been a problem on all old Mercedes for years - even from the old days when they used riv-nuts or whatever they were called. I think the old ones used to be aluminium and often they use brass inserts on the plastic panel models now.

But nice fix all the same

 

[350_Coupe]

Trying to drill out the broken screw presents problems in itself,

1. Screw is steel, threaded socket is aluminum, so the weak link is the socket
2. It's a threaded tube, the likelihood of much land to re-thread would be slim
3. Fibreglass panel, is not going to grip the tube massively well, and if it spins when drilling, it'll trash the hole.
4. Drilling into a 4mm (aprox) screw can be tricky, and skipping off the side and drilling out the side of the tube would be a highly likely !!
5. Knocking out old one would likely crack the fibreglass, and still leave a fairly large hole, could then use the well nut in that hole.


Lastly, for me anyway, the original fittings were still intact and water tight, so i figured best to find an alternative solution.

 

[350_Coupe]

Looks like the image links got killed so here's some replacements (hopefully in the right ordr as before!)

 

[350_Coupe]