HOW TO: Charger SRT-8 rear diffuser on a non Charger SRT-8 bumper cover

[carchitect]

Please note that not all the photos are in chronological order. There were a lot of two steps forward one step (or three) back moments. But I have arranged the writeup so as to spare yourselves those moments. Please let me know if you have questions, comments, or would like to point out that I may have missed a step.


Step 0:
Wait six months looking at the diffuser telling yourself “You know… I really should get around to putting that on.”

Step 1:
Gather your materials

-SRT-8 Air Diffuser (supplied by my wonderful SWMBO as a gift)

-Permatex Clear RTV Silicone Adhesive Item #80855
(I chose the cartridge as I wanted the control that a caulk gun would give me to lay down a continuous and even bead)

- (2) Body fasteners or plastic rivets (such as the kind that came with the Daytona front chin spoiler)
-Blue painters tape (for holding the diffuser in place while curing)
-Clay bar and dawn soap to clean and prepare the surface of the paint to ensure good adhesion.

Step 2:
Gather your tools

-Dremel with drum sander head attachment (if you do not own a dremel some 120 or 220 grit sand paper wrapped around a flat, skinny, rigid surface will suffice). You will also need the plunge cutter bit if you choose to follow an optional step.

-Wire cutters large and small. I found the small one was easier to use (i have them from a jewelry and metal smithing class I took in college).

-Utility knife (I ended up using my swiss army knife as I didn’t feel like searching for my utility knife)
-Caulk gun
-Drill with bit sizes 1/4" and below.

Step 3:
Start cutting

-UNDER PAIN OF DEATH DO NOT CUT THESE TABS OFF

-Start with the wire cutters and begin cutting the tabs in the fashion shown below.

BEFORE

AFTER

-Once you have worked your way around the diffuser you find that there are to flap like tabs at the very end of each side of the diffuser. Take your knife and score (this means lightly drag using a little pressure until you cut through the tab). See photo below on how to tell where to cut (the white line on which the knife is laying on).

-Now it’s time to bust out the dremel and start sanding down the remainder of the tabs. BE CAREFUL WHILE DOING THIS- you are working very close to a finished edge of the diffuser and I would hate to see you gouge it due to an unsteady hand. You don’t need to sand it flush, but it needs to happen as the tabs at this point still stick out past the finished surface/edge of the diffuser. I actually prefer to leave a little bit of the tab remaining… it provides more surface area for the adhesive (which is always a good thing).
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-Look for imperfections in the casting of the diffuser like this one shown here. Shave off with an xacto or utility knife.
[center]

Step 4:
Give the boys some air.

-Drop the 4 hangers that hold up the rear exhaust. There are 2 13mm bolts on each side (using a universal joint attachment on your socket will make this easier, so will using an impact gun :D ). Dropping these hangers will also give you the chance to add some washers upon buttoning up the exhaust if your tips aren’t even in the vertical direction. As you can see in the photos you can see a little surface rust starting a little anti-sieze on the surfaces will put a pretty good stop to that without having to resort to sanding and painting.

Step 5:
Wash your backside

-Since you are going to be working in this area I suggest that you get it very clean prior to even starting work.
-Dawn soap wash and clay bar the all surfaces within six inches of the diffuser location. After you clay bar dawn soap wash again and dry.
-Wash the diffuser with your dawn soap solution.

[carchitect]

Step 6:
This step is optional but I HIGHLY recommend it.

-PLEASE, PLEASE WEAR EYE PROTECTION WHILE YOU ARE DOING THIS. THERE IS A LOT OF DUST AND SOME LARGER PIECES CAN GO FLYING.

-Before doing this I also highly recommend taping up your exhaust tips (you really should do this anyway). I had a little slip with the dremel and the tape saved my behind.

-The cutout shape for the R/T bumper and the SRT bumper are different. The diffuser ends up putting pressure on the exhaust pipe cutout and will continue to resist even after you adhere the diffuser. While I don’t think this could cause the adhesive to fail I didn’t want to take any chances. So out comes the dremel.

-I used both the plunge cutter (rough cuts) and the drum sander head (finish work and smoothing) to shape and remove material so that the SRT diffuser doesn’t push against the existing exhaust cutout as much. This doesn't have to be perfect so close counts any cuts you make will be completely covered by the diffuser.

Rough cut

All smoothed out

-If you chose this step you will have to rewash everything and dust goes everywhere. I also suggest using a leaf blower/air compressor to remove the dust that settles up higher in the bumper cover.

Step 7:
Protection is key

-Cover the lip of the diffuser in blue painters tape like so

Step 8:
Are we there yet?

-There are 4 body fasteners (2 piece reusable rivet) connecting the bumper cover itself to some sort of structural plastic brace whose purpose is to keep the bumper cover from flapping more than it already does.

-Take a flat headed screwdriver and use it in one of the slots to begin prying these up. I suggest putting the screwdriver in and just giving it a 90 degree twist. That will pop it enough to get your fingers around it to pull the center piece out. Make sure you pull it straight out.

-Once the center piece is out remove the second piece. I suggest going from the other side and pinch the part that splits and push it out. Set these aside as you will need them soon.

-Grab the diffuser and set it on your exhaust tips (make sure they are cool first).

-Get back under the car with those 2-piece rivets and replace them sandwiching the tabs on the back/bottom of the diffuser between the bumper cover and the rivet. Make sure the rivet enters the hole for that plastic structural piece that I mentioned earlier. Snap those all shut.

-Take some of your painters tape and use it to hold up the diffuser in its final position making sure it’s nice and tight. Now start outlining the position of the diffuser on the bumper cover with tape. You don’t need to be perfect here, in fact I would suggest leaving about a 1/16th gap of paint showing. You don’t want the diffuser to overlap the tape while the adhesive is curing. You will have a hell of a time getting the little pieces of tape out that are embedded in the adhesive under cover of the diffuser.

[carchitect]

Step 9:
I like to call them speed holes

-At the very edge of each side of the diffuser you will find a hole for a body fastener. I suggest using a ¼” 2-piece rivet.

-Due to the position you are in (facing up, with a drill practically right above your head I suggest EYE PROTECTION for this part too).

-I started a small pilot hole and worked my way up to a ¼” bit. I found from my chin spoiler install that the plastic tends to suck the drill through if you try to bite too much, so be mindful of this because as soon and your drill breaks though it will want to just pull itself through instead of removing material (good timing and a well braced arm with prevent this). When you finish drilling the holes make sure the mating surface is clean and doesn’t have material shavings around it.

-Test fit the plastic rivets for these holes. You will have to work fast when you need to put these in and I don’t want you to be fumbling with so be familiar with how they work.

-If the adhesive ever fails (doubtful) this is what your diffuser will look like with the six mechanical fasteners holding it. It definately won't fly off, but it will look kinda ghetto.

-Pull the rivets set them near their specific hole so you’re not looking for them when the time comes to use them.

Step 10:
Home stretch

-At this point you should have done the following:
-Cut the tabs off the diffuser
-Cut out your existing exhaust cutouts to allow for better clearance
-Washed, clayed, washed, and dried the work area
-Taped the leading edge of your diffuser
-Taped your exhaust tips
-Taped the outline of the diffuser on your bumper with a 1/16th” clearance
-Drill the holes in the bumper for mechanical fasteners at either end of the diffuser

-Prep your caulk gun, and cut the nozzle of the adhesive so that you can put down a nice fat bead. (Those of you who have never handled a caulk gun before may want to buy a tube of cheap silicone from the hardware store and practice what is involved in putting down a nice even bead of caulk on a piece of cardboard).

-This stuff is STICKY so try not to get it anywhere you don’t want it.

-Prepare 5-6 pieces of long painters tape that is stuck to the diffuser with about 6-8” dangling free. (I suggest using 3” wide painters tape here).

-With the diffuser hanging by the 4 rivets on the backside of the bumper cover and resting on the exhaust tips start laying a bead of adhesive that basically follows the line of tabs that you cut off earlier. Make sure that adhesive sticks past the leading edge of the diffuser (that way you KNOW it will make contact with the bumper cover). Don’t be afraid to be liberal with the adhesive. I also put a bead following the approximate location of exhaust cutouts on the diffuser (I was able to tell where as they made slight marks from the test fittings). Don’t spend more than a minute or two doing (you really should shoot for 30-45 seconds until you are ready to lift the diffuser into place). You don’t want this stuff to skin over… then you will have problems. It will take longer than that to skin over, but I'm trying to stress the importance of doing this part quickly.

-Lift and push the diffuser against the bumper cover, using the painters tape to secure it in place. Pull it TIGHT and push on the diffuser a little as you do it. You will notice that a little adhesive has squeezed out of the seam. This is good as you know you have good bond right there. Don’t bother with cleaning them now, they will come off easily when they are cured.

This is what a tight piece of tape looks like, don't let the tape follow the outline of the bumper

-At this point snap in those two rivets at either end of the diffuser.

-Once you get the initial 5-6 pieces of tape up start taping more and more until you don’t see any gaps along the seam.

-I let the adhesive cure at least 12 hours prior to removing the tape. I’m sure you could remove it after 3-4 hours but I wanted to play it safe.

-Don’t forget to button up your exhaust hangers at this point.

Step 11:
Pulling the bandages off

-Easy as pie right? Wrong. If you managed to pinch any of the tape on the bumper cover under the diffuser you will have a hard time getting those little slivers of tape off. Otherwise this step is cake and is very enjoyable to watch the fruits of your labor unfold.

-If you do manage to pinch any tape good luck. I got a lot of mine out just by being able to catch an edge, the really stubborn ones I lightly scored it with a razor blade and then pulled it off with a tweezers. But this leaves a hint of blue in the seam. I’m gonna try and get the rest out with a fine but stiff detailing brush, but haven’t had a chance to give that a shot yet.

Step 12:
Durability testing

-While I was taking the tape off I pushed down pretty hard on diffuser and it didn’t budge at all. In fact it look like it deflected the bumper cover instead.
-Survived an extended and spirited drive (hey I had to test out my new rubber :D) with a few jaunts up to 80 MPH on the small section of expressway around here that isn’t under construction.
-Also survived a touchless high pressure car wash (Lazerwash 4000)


Final thoughts
While I had originally wanted to use a mechanical fastening technique I really feel that this adhesive will go the distance and is very strong. I have complete confidence in it to do its job. Total time from start to finish included the several breaks for photos and taking my time to think was probably 6-7 hours. I could probably do this in about 4 hours now that I know what to do and the order in which to do it. Those of you who are interested in doing this mod shoot me a PM and I would be more than happy to let you pick my brain over the phone. Those of you that are kinda local could convince me to help you for a meal and a beer if you think you can't do it yourself or don't have the proper tools.

[carchitect]

UPDATE:

I've gotten some PM's about durability testing and since it's been almost 8 months since I did the install I figure I ought to do an update. I've had absolutely no problems. There was a big doubt in many minds (heck I'll even admit my own) but the adhesive I chose has held up remarkably well. The car has seen ambient temps in the upper 90's all the way down to -1, as well as a few freeze/thaw cycles (not that it really applies to silicone but it emphasizes there have been many temperature changes).

It's been in direct sunlight, salt soaked, at highway speeds (possibly above too )

That baby isn't coming off unless you physically pry it off.

[BurntOrange]

good write up

[R/Tmatt]

^ pretty sweet and nice write up

[BigHemi06]

Very nice write up beans to you

[infernocharger07]

Thanks for the detailed writeup used it last weekend with success!