How to repair a plastic undertray?

[snyder]

I am working on a 3000 gt that has a shattered plastic undertray. It runs from the front bumper to the rear of the engine. There are holes, cracks and broken mounting tabs. I am thinking of grinding back the bad edges and fiberglassing it back together. I just dont know how well the glass will stick to the plastic. Any thoughts?

 

[Stuart in MN]

I looked at one of the Mitsubishi online parts sources. I'm not sure if I was looking at the correct part, but I found a panel that fits under the back edge of the front bumper selling for only $56.00. At that price I wouldn't spend time trying to fix up a broken one.

https://www.mitsubishiautopartsdire...trim/3-0l-v6-gas-engine/body-cat/spoiler-****

 

[p_mori7]

Agree with Stuart.

I recently changed the undertray on my wife's Kia Forte. It was only $50.

 

[kbs2244]

If you have to repair it, fiberglass will not work.
This is a golden chance to learn plastic welding.

 

[frank001]

I am working on a 3000 gt that has a shattered plastic undertray. It runs from the front bumper to the rear of the engine. There are holes, cracks and broken mounting tabs. I am thinking of grinding back the bad edges and fiberglassing it back together. I just dont know how well the glass will stick to the plastic. Any thoughts?

I repaired one on a VW Passat using fiberglass cloth. It was torn from front to back about half way. Worked fine. Still good when I sold it several years later.

 

[Stuart in MN]

Agree with Stuart.

I recently changed the undertray on my wife's Kia Forte. It was only $50.

I went through the same deal with my 1986 BMW M535i a few years back; it has an under tray that had gotten pretty beat up, and I was going to fix it until I priced a new one. I'm glad I bought it when I did as they were no longer available soon after.

 

[no704]

Junk yard

 

[theundermount]

does anyone else feel with newer cars parts are just not worth fixing anymore? seems like replacement is always cheaper

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[mike93lx]

does anyone else feel with newer cars parts are just not worth fixing anymore? seems like replacement is always cheaper

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I bet there is less waste generated by buying a replacement than what a repair would cost,especially in thia case.

 

[WoodsTruck]

I just fixed one on my kids '03 Outback.
I have a 60 watt soldering iron I use for this type work. If it is needing more strength, I will get it good and clean then cut small pieces of aluminum door screen and lay over the seam. Use the hot iron to press it into the plastic and smooth over.
On the undertray, you can "weld" from both sides to get max penetrative melting.

 

[bonneyman]

does anyone else feel with newer cars parts are just not worth fixing anymore? seems like replacement is always cheaper

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That's what they want you to think. There comes a point when it's not cost effective to repair something versus new, but I'll always take a crack at fixing it first.

For repairing plastic I heartily recommend Plastic Welder. Haven't found a plastic yet that it won't adhere to.

https://www.amazon.com/dp/B003NUGL9S/?tag=atomicindus08-20

 

[Stuart in MN]

does anyone else feel with newer cars parts are just not worth fixing anymore? seems like replacement is always cheaper

I wasn't saying he can't fix it if he wants to, just that if the price for a replacement part is low enough he may as well get a new one that isn't patched up.


One problem with fixing an undertray is going to be thoroughly cleaning off all the oil and grease and road dirt, so the fiberglass or glue or whatever is used for the repair will stick. Like I mentioned earlier I replaced a similar part on my car, but prior to that I had patched up the old one - what I did was use some metal strips and pop rivets to join together the cracks and to make new mounting points. It didn't look very good but it worked.

 

[shedfullatools]

- what I did was use some metal strips and pop rivets to join together the cracks and to make new mounting points. It didn't look very good but it worked.

This is what we almost always do to fix plastic snowmobile hoods or bellys, holds up excellent and really the best option on something as greasy and oily as the belly of a skidoo. Depending on the access available to the back we always either did two Identical sheets of aluminium sandwiching the plastic or just one on the outside with small washers on the rivets inside. If not this method a "drift stitch" also works great on areas that don't need to be terribly strong, that's my go to with atv plastics using color matching zipties