G-Body Rear Deck Speaker Adapter 6x9

***************Notice***************

This design is intended to be printed with 100% infill and may be subject to failing with less infill/few perimeters as it is a load-bearing part.

This design requires the original tab-style mounts in the rear deck.  Double check and make sure your car has identical speaker mounting to these pictures:

Introduction

This speaker adapter was designed specifically to fit modern 6x9 Kicker 3-way speakers in the 4x10 rear deck speaker locations of a 1986 Chevrolet Monte Carlo SS without cutting any sheet metal, drilling any holes or bending any trunk torsion bars, while utilizing the original speaker mounts.  With these, the car can be quickly and easily switched back to 100% factory form with the original 4x10 speakers and tray mount if desired.  This adapter should work in most other G-body cars with most 6x9 speakers.  The Kicker speakers I have linked are relatively large, so it is unlikely that speaker choice will cause fitment issues with the trunk torsion bars.  I cannot speak with absolute certainty to the fitment of these adapters to non-monte carlo G-body's, so if you make one of these for a different G-Body, let people know in the comments how it worked out for you.

This speaker adapter is mostly 3D printable, but will also require some 1/8" diameter rod(hard/stiff rod is better) and access to some common tools that should be available in almost every shop.  

I printed my adapters out of CF PETG, which is strong, has suitable temperature resistance for my geographic area, excellent layer adhesion, is quite stiff and provides somewhat similar acoustics to wood.  I recommend you also make yours out of CF PETG, PA6 CF, or possibly PETG.  I would advise against printing this out of PLA or ABS, as the poor layer adhesion of ABS will likely result in failure on the first rough road you drive down and PLA will eventually melt with the load of a heavy speaker installed. 

If you are sufficiently happy with how this design has worked out for you, please consider sending a donation my way if you are able: https://buy.stripe.com/bIY4i488N84rcCY3cc 

Notable Printing Considerations

• This is a load bearing part subject to the slightly cantilevered weight of a large speaker.  It is imperative that layer adhesion is very close to perfect and the part has 100% infill.

• It is recommended to print the parts out of CF PETG, PA6 CF, or some other material that has excellent layer adhesion, strength and good enough temperature resistance for your area.

• If printing with a carbon fiber-filled filament, ensure layer heights do not go below 0.2mm and try to keep a 0.25mm+ layer height where you can to prevent clogged nozzles.

• The adapter parts are quite large and may be subject to warping without a suitable enclosure or poor bed adhesion.

Parts List

Installation

Firstly, check that the speaker adapters fit in your car before going any further.  I can guarantee that they fit properly in a Monte Carlo, but have no confirmation that they 100% fit other G-bodys yet.

To remove the supports from the speaker adapter, use a knife to carefully separate the supports from the part as pictured working from the outside inward/more deeply and all the supports will pop right off as one big chunk, even with sticky PETG supports.

Ensure that there are no supports or print defects interfering between the speaker adapters and the tab mounts, and that they sit flush against each other.  If they do not, the strength of the adapter will be slightly compromised.

Clean out the brims from the four speaker holes, but DO NOT DRILL THESE OUT unless your specific speaker uses larger than normal screws.

You may want to run the speaker screws through the four holes in the speaker adapters so that they are easier to screw into later.  You may want to go “back and forth” a bit with the screw, as you will be tapping the threads in with the screw as you go.

Use a 1/8" drill bit to clean out the three holes on the side of the adapter near the top.  The idea is to have a nice, clean passageway to press-fit the 1/8" rod in.  DO NOT DRILL HOLES RIGHT THROUGH THE ADAPTER or the 1/8" rod could eventually risk vibrating out one day needlessly.

Use the same 1/8" drill bit to clean out each of the two holes on each of the tab mount parts.  Again, don't drill right through the parts.

Cut four 34mm lengths of 1/8" rod and grind any burrs or sharp edges off that will impact its ability to be installed into the holes.  Ensure these rods are less than 35mm in length or they will probably not fit in their respective holes.

Cut two 60mm+ lengths of 1/8" rod and grind any burrs or sharp edges off that will impact its ability to be installed into the holes.

Use a very small hammer or other similar tool to carefully tap the 34mm lengths of rod into the two holes on the side of the speaker adapter where the tab mount is installed.  If you are concerned that the rods may split the printed part, you can clean the holes out a little more with the drill bit to make the rods fit more loosely.  The rods should protrude no more than 19mm when fully seated.  If mistakes were made, you can carefully grind the rods down to the correct length while they are installed in the adapter, but be careful not to grind too much at a time and melt the adapter's plastic.  In the picture below, the rod on the right is an example of how one should look when fully seated, and the one on the left is not yet fully seated.

Carefully install the CORRECT tab mount to the speaker adapter and protruding rods.  You will have to carefully tap a little on one side and then the other repeatedly, ensuring the tab mount is pressed onto the rods straight and evenly until it is seated right against the adapter.  On my tab mount here, it didn't quite fully seat against the mating surface here due to slight over extrusion and the little tab on the other side of the tab mount pressing into the adapter.

Use the small hammer to similarly install the 60mm+ rods into the one hole on the speaker adapter opposite to the tab mount, in similar fashion to the other rods.  This rod should fit relatively tightly in the adapter so that it doesn't vibrate out later, so don't ream the hole out too much with the drill.

Install the 0.5" spacers on the 60mm+ rods.

Check the 4x10 speaker holes in the rear deck of the car.  You may want to move or cut out any material in the way of the hole that would deaden the sound.  Don't remove the board with the slotted speaker holes in it, or there will be nothing to prevent the carpet above from sagging down into the speaker.  Remember, the goal is better sound while keeping it essentially factory spec, not ideal sound.  A top-mounted speaker setup would definitely sound better, but would also involve cutting up the car a bit.

Install the speaker adapters to the rear deck of the car.  You will likely have to slightly bend down the singular tab closer to the center of the vehicle to pop the long rod in place.  If the spacers are slightly too short or long, there are shorter and longer spacers provided.

You may need to slightly bend the tab holding the 60mm+ long rod up to provide a firm seal against the rear deck.

Place your 6x9 speaker against the adapter and use the four speaker screws to attach it to the adapter.  If you have trouble fitting in the trunk to do this or forgot to run the speaker screws through the adapter before, you can alternatively remove the adapter once you know everything including the spacers fit properly, attach the speaker to the adapter, and then reinstall the whole assembly back in the rear deck.

Connect your speaker wires, play some music or test tones, and ensure that the speakers and adapters are tightly installed and do not vibrate.