While pulling the undertray to replace the oil and lower oil cover, I noticed my undertray was in bad shape. Like, really bad. I already had a few zip ties in holding up, but way worse than I expected. Most of the used undertrays on the market were in equally as bad of shape and were about $1,000, and a new one was over $2,000 shipped, so I decided I could learn how to fix it for much cheaper.

The undertray is made of fiberglass and has cutouts for certain things, like mounting points, rubber grommets for oil drains, and for the jack locations to use with your floor jack or lift. All of the undertray fiberglass surrounding the jack locations were disentigrated, so that was my main focus to fix. There were also a few other little cracks and spots missing materials.

I bought a large fiberglass repair kit on Amazon, which came with fiberglass mat, resin, a hardening compound, scraper and mixing tray and mixing stick. This kit came with enough materials to do 2-3 undertrays, and I will use the leftovers to do repairs on my fiberglass hot tub in the future. I also needed to use a few old paintbrushs to spread the resin on, worse gloves, and used some 3M tape.

Parts

• Bondo Fiberglass Repair Kit - $35
• 3M Aluminum Foil Tape
• Filler Primer Spray Paint
• Black Spray Paint
• Gloves
• Small Paintbrushes
• Sandpaper

My first step was to wash the undertray on both sides, I just sprayed it with the hose, then a degreaser, then scrubbed it, then sprayed it off again and let it dry.

Next, I used the 3M Aluminum Foil Tape to create an outline of what was missing on my undertray, so basically filling in all the broken off pieces. There was a lot of them. I started on the top side of the undertray, so the part which faces up towards the cars engine, which you can only see while the car is off. This way, if I mess up on my first attempt, it won’t be seen anyways.

This is where I started wearing gloves full time. After filling in the broken off pieces, I cut fiberglass mat strips to cover the tape and put them in the correct location. Having the strips pre-cut is ideal, since the resin cures pretty quick, I could do about 10 strips of resin per round.

Once you have your fiberglass strips ready, you can mix your resin and hardener and get started. The recipe on the bottle says to mix 1 oz of resin and 10 drops of hardener, then stir very well. I did not measuere exactly, I just poured some resin in the mixing container that filled it about halfway, added maybe 10-15 drops hardener, then stirred with the wooden stick. This is where it’s good to have an old workspace you don’t care about, since you will get resin places you don’t want.

Once your resin is mixed, grab your paintbrush and start working! I put some resin down on the old fiberglass, then placed the mat on top, then covered the mat in resin until it was soaked. I noticed the mat seemed to break apart if you actually “painted” it, so light strokes and letting the resin drip on it before seemed to keep the mat mostly in tact.

Repeat this for the whole top of the undertray. Let it dry for a while, I think I let it dry about half a day, then flip it over and repeat on the bottom (more visible) side of the undertray.

Once you have all the fiberglass filled in, cut out the excess, I had a lot around my jack points, I kinda wish I cut that before adding resin, because fiberglass is hard to cut.

If you want to make it look nicer, sand it now. Then add a filling primer on both sides, then a final coat of paint on both sides - I used a black semi-gloss.

The end result is GREAT, I am so excited about how much better it looks, and with all of the mounting points actually made of fiberglass now, instead of air, I can mount my undertray easier and without zip ties.

I also purchased Ferrari P/N 062678500 and 64783600, which are both rubber plugs that my undertray was missing that cover the 2 oil drain plugs. It was $13 for those 2 parts from Ricambi.

If you prefer videos, ferrarifxs on Youtube has two great videos on repairing a standard 360 undertray, and a 360 Challenege race car undertray, which is much different than a standard 360 undertray. It has more air vents and some mesh screens.