Cracked plastic bumper repair?

[daveduck]

Just wondering if it would be possible to repair the front bumper on my 1990 325i. I made a bonehead move and accidentally dropped one side on the ground trying to put it back on and it cracked pretty badly. Is this worth trying to repair? I'd like to not have to shell out hundreds for a new bumper. I got some color matched paint, so I plan on doing the painting myself, while I paint the new sunroof panel, skirts, and iS lip. Thanks

[Slybeanx]

You could try using bondo or an epoxy on the inside, try to seal the crack as seemless as possible. If that still shows too much for you, then add on the outside if its still visible, sand it down and apply paint if needed.
Thats what I would do, but I'm sure there may be better ideas.

[rturbo 930]

I have a bumper to repair as well, so I'll be following this thread. I'm thinking plastic welding of some sort or an appropriate adhesive (I think I recall Jordan using an adhesive to modify the bumper on the red car) might be the way to go. Using bondo to fix the crack is definitely not the best method.

[daveduck]

I picked up three of these jb weld epoxy plastic bonder tubes https://www.homedepot.com/p/J-B-Weld...133H/303710788

It says it's good for bumpers so I'll try my luck. It won't be the first time I've used epoxy. I've almost finished up some taurus side skirts that were in terrible condition which required filling in some gaps and such. It's an absolute pain trying to sand the epoxy and get it flat with the rest of the piece, but it does work.

But anyways, I will keep this thread going with my progress. Hopefully I can do a decent job.

[daveduck]

Ok, I’m a bit stuck. Does anyone know how to disassemble the inside of the bumper? I am not sure if I will be able to epoxy the inside of the bumper. The white part looks like it comes out (not exactly sure how though), but the grey part is attached to the rest of the bumper, and I don’t think it’s removable.

The black part with the nuts I think is only attached to the white long piece. But I don't think that can be removed anyways. I sheared off one of the bolts trying to loosen it, and it had red loctite on it.

[roguetoaster]

I thought it was a combo of those tabs at the back and a set of plastic rivets from the front.

[Slybeanx]

I have a bumper to repair as well, so I'll be following this thread. I'm thinking plastic welding of some sort or an appropriate adhesive (I think I recall Jordan using an adhesive to modify the bumper on the red car) might be the way to go. Using bondo to fix the crack is definitely not the best method.

You are right I said bondo but I meant JB plastic weld lol

[daveduck]

Step 1: Take off black plastic trim. It can be pushed out from the inside. NOTE: there are small holes where you can stick a screwdriver in from the inside to push out the tabs. Shine a flashlight inside to see them. Proceed to break multiple tabs :)




Awesome, broke off another fat piece getting the trim off :)




The outside piece is held onto the inner white piece with these rivets that go through. I believe you are supposed to push these through so that the split part is skinny enough to fit through, and the white piece can be removed. Half of mine seemed absolutely seized in there, and would not come out. So a bit of dremel work and they are destroyed.



This is what it looks like when you push it through.





Note: There are two black colored rivets that are hidden. They go under the pieces that are bolted down that I wasn't able to remove. They are in this area








And seperated! Once the rivets are out it simply lifts up.

[daveduck]

Anyways, upon further inspection, there are just too many cracks... It's hard to tell from the photos, but there are probably 6 or 7 cracks, with most of them being fairly large. A couple of them are positioned to where I would have a tough time repairing it from the inside, so I am not confident that I would be able to get it structurally sound enough that it wont crack in the future. I think that I'll just go ahead and buy an uncracked front bumper. Maybe I will give this a shot just for the hell of it though.

[roguetoaster]

Body shops do plastic welding all of the time. The basic process as I understand it is to preheat the part, use a hot tool to make a molten puddle with the material and fill rod, then cool the workpiece in some sort of controlled way. If you wanted to replicate that you'd need to determine what plaatic the bumper cover is made of for starters.

[daveduck]

Body shops do plastic welding all of the time. The basic process as I understand it is to preheat the part, use a hot tool to make a molten puddle with the material and fill rod, then cool the workpiece in some sort of controlled way. If you wanted to replicate that you'd need to determine what plaatic the bumper cover is made of for starters.

Yeah, I've looked into plastic welding which definitely seems like it would work well, but the issue is that there isn't a way to get under the main piece that is broken. Hopefully you can tell from this picture, but there's a piece that's attached to the bumper that can't be removed (from what I can tell), and it sits directly under the main crack in the bumper

[roguetoaster]

Ooh, rough. Maybe clean it all with a solvent and just use a quality plastic epoxy?