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Discussion Starter #1
I’ve never repaired a damaged plastic bumper cover, but the original one on my 98 had some damage that was going to be hard to sort out, and the best one I could find at the junkyard had a “y”-shaped crack that was probably close to 6” long at the longest point. It had been sitting in my garage for a while, and along the way I had picked up a cheap plastic welding kit at Harbor Freight. I had some family in town this weekend helping around the house, which was fortuitous as this turned out to be at least a four-hand job.

After looking over the kit’s rather minimal instructions, I started in on the repair attempt by grinding a bevel into each side of the crack with a rotary tool. I normally would have done this from the back, but the crack went under the inner structure of the cover.

After the crack was a “V” shape along its whole length, I held the cover in shape, closing the crack, while my assistant used the hot iron and a bar of flexible plastic filler to get a tack weld in place to hold the crack shut. As it turns out, the suggestion in the kit to pour cold water over the repair was a good one, as it takes a long time for the weld to set up otherwise. After turning the cover over and repeating the process to close the bottom of the crack, where it crossed the flange between the body and bumper cover. Once the crack was completely closed, I went about using the iron and plenty of the filler material to seal and fill the rest of the crack.
2655682


The kit also came with some metal mesh that appears to be stainless steel to use as reinforcement. I cut a piece of that to cover as much of the crack as I could reach, and a little bit of extension past the end. Following the directions, I heated the mesh and bumper cover under it at the same time. Once it was stuck in place, I started working my way around the mesh, heating it and the plastic under it, while adding filler to the area of repair to seal the mesh to the cover.
2655685


After the repaired area was cool and hardened, I sanded the excess material down to look for low spots. I filled those with Bondo/3M bumper repair material. It must have been old, because it took forever to set up after being mixed per instructions. Last night, I sanded that down and applied a second coat of a different bumper repair filler/adhesive.
2655686

I’ll sand that tonight and see if I can get the profile right.

This was a totally new-to-me project, and at the very least I can safely say that the repair seems to be very strong.
 

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2000 E 320 Wagon + 2002 ML 500 SUV
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Sam, great job.

I also have a decent sized front bumper crack that had been repaired by a body man friend back in Summer 2016.

It's back and has been since last year. He stated at the time that it was a mixed bag to try this repair and said:

"Benz just uses some plastic that is more difficult for the repair to last than other car makes & I don't know why..."

I've seen this new space age glue adhesive called 'Bondic' pop up ads on YouTube.

Cures with UV light - y'all seen it ?

Same stuff my dentist used on my composite tooth filling...

David

Maybe that stuff would be the charm ?
 
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ML320 W163 2000 189 7 seater
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I’ve never repaired a damaged plastic bumper cover, but the original one on my 98 had some damage that was going to be hard to sort out, and the best one I could find at the junkyard had a “y”-shaped crack that was probably close to 6” long at the longest point. It had been sitting in my garage for a while, and along the way I had picked up a cheap plastic welding kit at Harbor Freight. I had some family in town this weekend helping around the house, which was fortuitous as this turned out to be at least a four-hand job.

After looking over the kit’s rather minimal instructions, I started in on the repair attempt by grinding a bevel into each side of the crack with a rotary tool. I normally would have done this from the back, but the crack went under the inner structure of the cover.

After the crack was a “V” shape along its whole length, I held the cover in shape, closing the crack, while my assistant used the hot iron and a bar of flexible plastic filler to get a tack weld in place to hold the crack shut. As it turns out, the suggestion in the kit to pour cold water over the repair was a good one, as it takes a long time for the weld to set up otherwise. After turning the cover over and repeating the process to close the bottom of the crack, where it crossed the flange between the body and bumper cover. Once the crack was completely closed, I went about using the iron and plenty of the filler material to seal and fill the rest of the crack.
View attachment 2655682

The kit also came with some metal mesh that appears to be stainless steel to use as reinforcement. I cut a piece of that to cover as much of the crack as I could reach, and a little bit of extension past the end. Following the directions, I heated the mesh and bumper cover under it at the same time. Once it was stuck in place, I started working my way around the mesh, heating it and the plastic under it, while adding filler to the area of repair to seal the mesh to the cover.
View attachment 2655685

After the repaired area was cool and hardened, I sanded the excess material down to look for low spots. I filled those with Bondo/3M bumper repair material. It must have been old, because it took forever to set up after being mixed per instructions. Last night, I sanded that down and applied a second coat of a different bumper repair filler/adhesive.
View attachment 2655686
I’ll sand that tonight and see if I can get the profile right.

This was a totally new-to-me project, and at the very least I can safely say that the repair seems to be very strong.
My bumpers are wrecked, especially the front one which had an argument with a van's tow hitch... I think it is too far gone to repair but I was wondering whether it could be reinforced from behind with aluminium sheets and araldite. I'm hoping it won't fail the MOT as it had an advisory last time. I'd rather get steel bumpers than replace them with the rubbish plastic ones again, but the best steel bumpers I've seen are made in Tbilisi, Georgia by RR factory, and that would be a 6k mile round trip to have them fitted...
 

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Yes, that is how it is done. For large holes, cracks and missing pieces, use a fiberglass type mesh on the back side (dry wall mesh works), for a backing and stability just like repairing a hole in drywall. (scuff the backside with 80 grit sand paper) Secure mesh in place to bumper with 3M Bondo Bumper Repair, then run a skim coat over the back side (so when working from the top, it doesn't run through) and let dry. From the top of the bumper, apply more repair material, leveling up to just over the bumper front surface, and let dry. Now sand down to the level of the bumper, finish sanding, prime, and paint. Finish with 2K clear coat (wear respirator, or die of hardened epoxy in your lungs) and have a great final result. I call it a 10-footer repair. (can't see the repair 10 ft or more from the car)

You can also use 10 min epoxy for holding the mesh in place and the skim coat- it's not as flexible as the 3M material, but it works just fine.
 

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2003 W163 ML350
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The bumpers on the w163 MLs are hard plastic and they get brittle over time. If the body and the paint of your vehicle is in good shape, I would replace them with new aftermarket bumpers and get them nicely painted. This what I did for the rear bumper that was damaged by a hit and run incident. After that accident my wife backed into my friends prius and the rear bumper literally shuttered into small pieces. That has a couple of years ago. I ordered it online and already had a bodyshop that is good at painting. They painted and mounted it for 200 bucks. I think I paid around 300 bucks for the bumper itself. Tried to find the exact price and seller in my mailbox but couldn't find it. If you really want use a product to fix it Bondo is the way to go. I used Bondo Glass before to repair some rust holes on the rear fenders of my tractor. It has been holding up well even on an old tractor with all the vibration. Good luck!
 

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W163 and General M Gremlin
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Nice to see others tackling plastic weld. :)

Bumper composite on the w163 is PC-PBT (xenoy).
Been playing around plastic weld for awhile now. Technology has advanced quite a bit from 10 years ago.
You need to beware of the specific plastic composite of the bumper material before welding and using the bold materials. w163 use the older, more brittle plastics (hence they crack very easily)
I back up all my welds (where possible with wire mesh melted into the backside first and then fiberflex for this type of composite - better than fibre glass paste) or you can V-groove back first, use fiberflex to fill with a hot shoe iron (glorified soldering iron) 100V is ok, 220V iron is best.
Let it cool properly and then proceed to V-groove the front
Note: I learned.... Surface and repairs have to be absolutley clean and the area you weld is free of ALL paint, primer and all the other stuff that builds up, collects on the surface. Use 99% iospropanol (cheap stuff from the drug store) to clean the surface after sanding thru to the bare plastic. Dont use anything else. The plastic aerosol cleaner you get from the shops is the same thing, just more $$

w124 bumper - 2 piece damage - Before and after bumper cover (same procedure with bumper strip)
Screen Shot 2020-10-14 at 5.59.11 PM.png Screen Shot 2020-10-14 at 6.04.20 PM.png Screen Shot 2020-10-14 at 6.05.36 PM.png Screen Shot 2020-10-14 at 6.07.29 PM.png Screen Shot 2020-10-14 at 6.00.15 PM.png
 
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I just googled and there are new front bumpers under 200. Prices must have gone down since I bought one. Small cracks can be fixed but if it is big and the SUV is nice looking, I would buy a new one instead of putting a lot of elbow grease on it.
 

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I’ve never repaired a damaged plastic bumper cover, but the original one on my 98 had some damage that was going to be hard to sort out, and the best one I could find at the junkyard had a “y”-shaped crack that was probably close to 6” long at the longest point. It had been sitting in my garage for a while, and along the way I had picked up a cheap plastic welding kit at Harbor Freight. I had some family in town this weekend helping around the house, which was fortuitous as this turned out to be at least a four-hand job.

After looking over the kit’s rather minimal instructions, I started in on the repair attempt by grinding a bevel into each side of the crack with a rotary tool. I normally would have done this from the back, but the crack went under the inner structure of the cover.

After the crack was a “V” shape along its whole length, I held the cover in shape, closing the crack, while my assistant used the hot iron and a bar of flexible plastic filler to get a tack weld in place to hold the crack shut. As it turns out, the suggestion in the kit to pour cold water over the repair was a good one, as it takes a long time for the weld to set up otherwise. After turning the cover over and repeating the process to close the bottom of the crack, where it crossed the flange between the body and bumper cover. Once the crack was completely closed, I went about using the iron and plenty of the filler material to seal and fill the rest of the crack.
View attachment 2655682

The kit also came with some metal mesh that appears to be stainless steel to use as reinforcement. I cut a piece of that to cover as much of the crack as I could reach, and a little bit of extension past the end. Following the directions, I heated the mesh and bumper cover under it at the same time. Once it was stuck in place, I started working my way around the mesh, heating it and the plastic under it, while adding filler to the area of repair to seal the mesh to the cover.
View attachment 2655685

After the repaired area was cool and hardened, I sanded the excess material down to look for low spots. I filled those with Bondo/3M bumper repair material. It must have been old, because it took forever to set up after being mixed per instructions. Last night, I sanded that down and applied a second coat of a different bumper repair filler/adhesive.
View attachment 2655686
I’ll sand that tonight and see if I can get the profile right.

This was a totally new-to-me project, and at the very least I can safely say that the repair seems to be very strong.
By the way that bumper doesn't look bad will probably hold up for many years to come. Good job. Nicely sand prime and paint it and have a beer on the house after you are done. ;)
 

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1998 ML320
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Discussion Starter #9
When I’ve looked around at replacement bumper covers, they all seemed to be the post-facelift style. This one was nice and straight other than the crack. Whatever plastic HF puts in their cheap plastic welding kit as the filler rods seems to react well with the material Mercedes used to mold the covers 20+ years ago. When I used the iron to melt the edges of the crack and the flexible filler rod at the same time, it all fused together nicely.
 

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2002 ml55
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Bumper composite on the w163 is PC-PBT (xenoy).
Been playing around plastic weld for awhile now. Technology has advanced quite a bit from 10 years ago.
You need to beware of the specific plastic composite of the bumper material before welding and using the bold materials. w163 use the older, more brittle plastics (hence they crack very easily)
I back up all my welds (where possible with wire mesh melted into the backside first and then fiberflex for this type of composite - better than fibre glass paste) or you can V-groove back first, use fiberflex to fill with a hot shoe iron (glorified soldering iron) 100V is ok, 220V iron is best.
Let it cool properly and then proceed to V-groove the front
Note: I learned.... Surface and repairs have to be absolutley clean and the area you weld is free of ALL paint, primer and all the other stuff that builds up, collects on the surface. Use 99% iospropanol (cheap stuff from the drug store) to clean the surface after sanding thru to the bare plastic. Dont use anything else. The plastic aerosol cleaner you get from the shops is the same thing, just more $$
great info here... i have played around with this as well ... one can get a plastic weld iron (soldering iron like thing with sample plastic melting rods)... for $24 at harbor freight (or $18? ... either way... cheap)

agree about the wire mesh.... and also can use box staples...straightened and then melted down into the plastic

what plastic did you use to do the melting ? ... i have had varying degrees of success ... some just peel right up and off after cooling... i guess this is where one has to be very specific as to the type of plastic being melted...
 

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W163 and General M Gremlin
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great info here... i have played around with this as well ... one can get a plastic weld iron (soldering iron like thing with sample plastic melting rods)... for $24 at harbor freight (or $18? ... either way... cheap)

agree about the wire mesh.... and also can use box staples...straightened and then melted down into the plastic

what plastic did you use to do the melting ? ... i have had varying degrees of success ... some just peel right up and off after cooling... i guess this is where one has to be very specific as to the type of plastic being melted...
Yah, I've also use the heat stapler (not so on bumpers yet, but can certainly be applied to, if required - used on other plastic applicance part repairs to hold broken plastic parts together such as a toaster lever.
It's a glorified soldering iron where you insert the various shaped staples onto the end of it, it heats up and then you literally "brand" the two sections together (as you described) and melt it into the plastic, and then remove the iron quickly. Let it cool and snip the protruding legs off, flush to the plastic surface. Almost like surgical stitiching.
Our boy toys, eh?? :)

For the composite material on our ML bumpers, if you want to JUST use plastic and not the fiberflex rods, you can. The plastic MUST match up (ie.PB-PCT (xenoy) ). You will see this embossed onto the backside (somewhere) on the bumper parts. If it doesn't bond, it's not a match material.
This includes the AMG fender flares - same composite. All you need to do is melt down the plastics** (after cleaning them and removing all the paint, primer and wiping down the surfaces with 97-99% isopropanol) with the shoe iron.
I've done it with a heat gun too, but I prefer the iron - better control. If you do a plastic melt bind procedure, you need to make sure all the surfaces are at room temp or above when combining (melting) so that means heating them up if you're working in a colder or outdoor environment. Also, for safety, use a good quality painters respirator, especially with the iron.and prolonged applications.
** That's why anytime is see a nasty looking damaged front or rear bumper in pieces, I snap the these parts (cost nothing) and keep them as scrap material to use - various sections: flat, corners, rounded, etc. Then you can cut to size and shapes to fit into the missing spaces of your damaged bumper. Ive even taken for free a cracked w201 front bumper (really thick suckers) and cut them up as I need to plastic weld. Same material composite as our w163s, just thicker.
If you do not have access to these broken parts, the other best option is using rods. I use ones called "fiberflex" rods or strips and they have fiberglass embedded in these strips/rods. They bond exceptionally well to our bumper composition, stay flexible after application and are easy to sand down to paint prep finish with an orbital sander, air or electric 110V (I use both). No need to "mix or mush" this into the plastic itself. Just v-groove the crack lines at a slow speed to prevent the plastic from melting, and sand the edges, wipe down with ios, blow dry it and apply the fiberflex into the v-groove. Make sure the rod or strip has been melted with the iron before applying it into the v-groove and use the shoe iron to smooth it into the v-groove.
Much easier and faster to work with vs. fiberglass mix (plus fibreglass stays hard and is unforgiving, imo)
I also use aluminum body tape on the back side or front side depending on which side I attack first (usually attack the backs side first so tape applied to the front) - back side needs no finishing.
 
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Of course there is an ebay seller that I have used when the bumper skin is missing so much of the material, or you don't want to spend the time doing a large repair and repainting project.

mbiauto sells a decent finished, painted and clearcoat bumper skin that you can just replace yours with.

I ordered one a couple of years ago when my wife decided to push a shopping cart out of the way with the front of our ml350 so she could pull into the parking spot. Of course it was stopped by a concrete parking bumper that she said she never saw. Split the bumper across the front into pieces. True story. :(
 

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W163 and General M Gremlin
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Of course there is an ebay seller that I have used when the bumper skin is missing so much of the material, or you don't want to spend the time doing a large repair and repainting project.

mbiauto sells a decent finished, painted and clearcoat bumper skin that you can just replace yours with.

I ordered one a couple of years ago when my wife decided to push a shopping cart out of the way with the front of our ml350 so she could pull into the parking spot. Of course it was stopped by a concrete parking bumper that she said she never saw. Split the bumper across the front into pieces. True story. :(
Good info shared here camobob, cheers. (including your experiences).

US MB owners have the benefit of options, choices such as plentiful PnPs (like a 711, or Casey's, etc. imo) and cheap access to parts, new and used, with good inventory.

Come over the 49th parallel?; you need to be more resourceful, (just like up in Alaska). We don't (or least I dont anyways), leave scraps behind; same when I'm hunting. :)
Looking for ML55 bumpers (needle in a haystack), or even the regular stock, as an example, is pricey - used and new. Everybody up here parting out their vintage/old rides take the blue pill daily, and are all banking on a lotto win (as they brush away the 1,2 year old cobwebs on their parts car rusting away.)

My good friends, members on the other side of this imaginary line are helpful and resourceful too, and so accessing cheap resources is good, even with currency exchange and whatnot.
But hey, this is a DIY forum. Do what you gotta do, I think we all have more time on our hands right now, and certainly as you get older.
PLUS, you get alot of free meals and beverages from the neighbors - we all gotta eat n drink. :)
 
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Discussion Starter #14
great info here... i have played around with this as well ... one can get a plastic weld iron (soldering iron like thing with sample plastic melting rods)... for $24 at harbor freight (or $18? ... either way... cheap)

agree about the wire mesh...
That’s the kit I used. It also came with a decent-sized piece of metal mesh for reinforcement purposes. I didn’t need much of it for this job.

There were a few places on both the front and rear bumper covers where the original heat welding between the inner structure and the outer cover had broken. I used the iron to fix those, without the use of much filler.
 

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W163 and General M Gremlin
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That’s the kit I used. It also came with a decent-sized piece of metal mesh for reinforcement purposes. I didn’t need much of it for this job.

There were a few places on both the front and rear bumper covers where the original heat welding between the inner structure and the outer cover had broken. I used the iron to fix those, without the use of much filler.
Be cautious of the metal mesh provided in these kits. The gauge of ss wire included can be very light and flimsy. If you can easily bend them with one hand or when you cut them and the mesh joints separate easily, the gauge/quality is subpar, imo.

This is what I use - ss304 grade. You will notice the difference in grade/quality when you use this for a repair.
 

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Discussion Starter #16
Be cautious of the metal mesh provided in these kits. The gauge of ss wire included can be very light and flimsy. If you can easily bend them with one hand or when you cut them and the mesh joints separate easily, the gauge/quality is subpar, imo.

This is what I use - ss304 grade. You will notice the difference in grade/quality when you use this for a repair.
It’s fairly light, but it was also pretty hard to cut. The heat welding was holding the crack shut alone, I added the mesh on the back more for redundancy and peace of mind than any real feeling that the welded area may crack again.
 

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W163 and General M Gremlin
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It’s fairly light, but it was also pretty hard to cut. The heat welding was holding the crack shut alone, I added the mesh on the back more for redundancy and peace of mind than any real feeling that the welded area may crack again.
Manual hand snips or dremel tool? :)
The latter is quick.
 
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