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1997 SL500 70K Miles
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Discussion Starter · #1 ·
I'm thinking about fixing this crack with a band of 3M 08237 and an embedded Simpson galvanized mending plate across the crack. I'd also add a flat aluminum bar (1/2" or so in width) on the bottom lip with either rivets or bolts (there are already a few factory holes there that could be utilized). The bar would also serve as a mounting point for old fashioned curb feelers that would stick out forward a few inches so this doesn't happen again. Comments or suggestions?

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1996 SL500, former 1986 560SL
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472 Posts
I did similar on mine. The previous owner had tried to repair the crack, but it simply re-cracked. Like your thought on the flat aluminum bar, I fabricated a stealthy piece from 1/2" x 1/8" steel mounted on the inside edge that reinforced the entire bottom edge. It required some fabrication and welding to be a single piece (there are a few obstacles to go over) pop rivetted in place along the bottom. I have even contacted those pesky parking-spot curbs with no new damage.

I then used the flexible type bumper filler to repair 1 crack similar to yours and 1 smaller crack. I used the fiberglass screen/mesh to reinforce the crack repairs (edit on the inside). The flexible bumper type filler is more expensive but worth it and it is really easy to use. It cures fast and is very easy to sand and finish and remains flexible enough.

As long as you make the bottom edge very stable with reinforcment, the rest of the repair is relatively easy. You need to use something strong enough to hold the desired lower edge shape. The reinforcement of the bottom edge does interfere with the factory mounting of the front inner fender liners where they mount at the bottom of the bumper, so you need to use some different (longer) fasteners for that. I removed the bumper cover for the repair and recommend that for anyone doing this repair.
 

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1990 300SL24 114mi
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186 Posts

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2002 SL500
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329 Posts
inexpensive...
And R129's are incompatible.
$18 plastic welder from HF.
Plastic welding isn't hard. This repair is straight forward. Fasten tear together to ensure straight alignment, weld from back and front, sand, paint. But you need to weld with the same type of plastic. Those general-purpose sticks won't hold. My guess is its polycarbonate.
 

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89 190E 2.6 x2, 99 SL500 Sport
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+1 for plastic welding. I just had major body work completed on my R129. My front bumper was pretty trashed (cracked all the way through), plus had a hole punched in it and some other random cracks and holes from the front license plate. All the repairs were done with plastic welding and the bumpers look brand new. From what I was told they wound up using the stainless steel backer mesh.

Otherwise if you want the "poor man's repair" sand the back side down, and get some JB Weld Plastic Weld, cut some scrap plastic as a backer and clamp everything together. That's how my bumper was "temporarily" repaired until the bodywork.
 

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95 SL600
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960 Posts
Adhesives won't work. Take it to a body shop to have it plastic welded.
That’s silly, get yourself some SEM 40507 quick set 50 and SEM 70006 plastic repair reinforcing tape. Clean the back area with laquer thinner, scuff with 80 grit around area, make sure you have the part in the correct shape and glue with reinforcement tape behind. This stuff sets in 50 seconds so don’t mix a great amount.
Drill a small hole if snd where the crack stops so that it won’t keep going. If you like you can drill 1/8 holes on either side of the length of the crack and push the glue down in the holes to hold it together more.
You can also chamfer them front snd back of the crack and put the glue in there as well. It’s black glue and if done clean and with mechanical adhesion ( 36 or 80 grit) will stay. If you question its strength just get it on your fingers snd let it harden, it’s almost as difficult as getting POR15 off which is almost impossible.
 

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1998 e430
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539 Posts
i'd diy with a plastic welder; 80 Watt Iron Plastic Welding Kit

lots of videos showing how to, you melt the screen into the plastic on the backside. you can reinforce by using similar plastic to add thickness to the repair area. this repair plastic can be "harvested" from somewhere else on the fascia or, better yet, get a scrap fascia from a local salvage yard.

if you're careful and get the sides of the crack tight, you'd probably barely notice from the front side!
 

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89 190E 2.6 x2, 99 SL500 Sport
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If you want to see plastic welding in action, here's a couple posts from my recent thread
 
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1998 SL500
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Just repaired a badly cracked (aluminum plate pop riveted across the crack) front cover. Used similar material to you to repair the crack, Grooved the crack & embedded fiberglass cloth:

For the main repair of the cracked area & reinforcement on the back side, I used this:

For your finishing steps, a material like this is the ticket (I live a few miles from Eastwood's warehouse fortunately):

Other brands out there of course (SEM bumper bite) Finding a small quantity of the professional grade material was the challenge, This applies thin, to get the final finish before priming with flexible primer.
 

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95 SL600
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960 Posts
Really? Where I come from, taping your car together is silly.
Maybe you should try the product I recommended. Then you would realize how silly your statement is. I took a cls55 bumper that was in the trunk of the car in 3 pieces and used these products to put it back together. My wife drives the car and has dragged it over parking curbs and other things without any damage. Plastic weld from the hardware store is not good, but these adhesives are very strong.

I have used these adhesives on countless parts, with the correct preparation, they are very strong and durable. I like this one because of the quick cure time. SEM products are quality products for professional repair.
 

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W163 and General M Gremlin
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11,653 Posts
You have PC PBT Xenoy bumper covers.
Easy plastic weld fix using fiberflex rods. I've done a few of these for myself and on neighbors w124 rides, using basic tools - soldering iron, s/s wire mesh and, if you have (not necessary in your situation), spare pieces of the same bumper cover material. Your repair will be stronger and more flexible than the surrounding, aged and brittle area around it.
It's fast, and a straight forward fix.

 

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1998 Red SL500, 2002 Black SL500, 2014 Black E550 Cabriolet
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1,392 Posts
Why not just buy another bumper! Plenty available and many aftermarket bumpers available. Do some....adjustments on the replacement bumper and it will be just as good as the original....
 

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1996 SL500, former 1986 560SL
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472 Posts
Why not just buy another bumper
True for most perhaps, but my apprehension on doing that was based on the fact that the low-hanging design of these bumper covers makes them prone to getting re-damaged. This is the only car that I have ever had that hangs so low in the front... couple that with the fact that I'm a slow learner (apparently, just like the previous owner of my car)... :)
 

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89 190E 2.6 x2, 99 SL500 Sport
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True for most perhaps, but my apprehension on doing that was based on the fact that the low-hanging design of these bumper covers makes them prone to getting re-damaged. This is the only car that I have ever had that hangs so low in the front... couple that with the fact that I'm a slow learner (apparently, just like the previous owner of my car)... :)
I was at a car show last summer and there was someone w/ a R129 who actually put one of those front license plate cameras on so they wouldn't hit the bumper.
After getting mine fixed, I just stick to backing in spaces to avoid messing things up.

I know w/ a collision shop, they would typically just replace the bumpers if they're badly cracked. With my case, I used a vocational school and they spent something like 60 hrs of labor plastic welding and refinishing the front/rear.
 

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2002 SL500 Silver Arrow, 2001 SL600
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I have two friends that own collision repair shops -- both very successful. One friend said he'd find me a new front bumper cover -- haven't heard back since Nov 25th. Not sure many sport package bumpers exist -- at least at a reasonable price.

Other shop has my bumper cover right now -- doing the plastic weld.
 
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