Factory JBL sub rebuild


Staff member
Sep 12, 2023
North Ridgeville, OH
Vehicle Details
1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Back in 2013 I got my hands on a factory subwoofer box from a 92-94 SC which had a blown speaker (like almost all do). To my knowledge the original is a 6.5" JL driver, but it's fairly easy to retrofit a slightly larger 8" into the box with minimal modifications.

To repair my sub, I purchased a JL 8W1V2-4 driver, some polystyrene glue from Home Depot, a pack of pan-head machine screws and nuts, and used an extra 1/2" styrofoam insulation sheet I had laying around. I opted to use 14 AWG stranded wire, but depending on the power handling ability of your amp and speaker you may need to go up to 12 AWG.

Step one is getting the box opened (remove the 7 screws and gently pry apart the seam) and removing the old speaker driver. Once that's done, set aside the green foam batting that is inside - we will need it later.

Place the speaker driver over a scrap piece of cardboard, then mark and cut the cardboard to the perimeter of the driver up to the housing (it will be about 8"). Center that cardboard over the outlet of the enclosure. Chances are the template will bump up against some contours in the molding - don't worry about that for now. Once it's centered, mark it with a marker that is clearly visible on the black plastic.

Once you've marked the template on the box, use a cutting tool (Dremel or similar) to cut away the extra plastic in the outlet so that the hole is as wide as the speaker diaphragm. See below for what you should end up with:


Next we'll tackle the problem of that plastic lip that the speaker bumps into. This is where the styrofoam comes into play. Draw with a black marker a circle with the cardboard template, then using the speaker itself as a template, center it on the template and then mark the perimeter of the speaker. Cut out what the ring, then dry fit it against the mark/hole in the speaker and cut away at an angle the section that bumps up against the contour of the housing. Be sure the styrofoam sits flush up against all surfaces in the box, as it will be what we use to get a tight air seal from the flat plane of the speaker housing to the uneven sides in the box. You should end up with a ring that looks like this:


Next, set the styrofoam ring on the speaker and push the machine screws through its mounting holes and the foam. This part is a little tricky - so take care and be patient - but mark the locations of the mount holes on the top of the enclosure and drill them out.

Once you're satisfied that everything fits, apply some styrofoam-safe glue to the box, and affix the ring to it.


Place the speaker on the ring and screw it into place.

Route your speaker wire through the side of the box, then reinsert the green batting. This increases the density of the interior of the enclosure and mimics a larger box without any filling. This improves acoustic performance of the box.

Seal the edges and close up the box, then reinstall with the amp of your choosing!


I'm doing a JBL subwoofer replacement this week. I have the old sub removed, and a Pyle, PLPW6D 6.5" sub should be showing up today. I plan on using the original JBL amp. My question is what impedance should I wire it at. It is dual coil, so should I run it at 4, or 8 ohms. The amp is 6 ohms. I am planning on running both coil wiring outside of the box, so I can change it between 4, or 8 ohms. I'm old, and my ears can't take the beating, like they used to ;), so good enough is OK. Just don't want to blow the stock amp. Thanks for the write up, and pictures.
That's super cool. Must be a rather rare option.
It's commonish on SCs. LXs and Cougars with it are definitely rare.
The og driver was a jbl; it was an extra option with the premium sound, and dc changer. I have 2 of the 6.5" drivers here, they were in my dads stuff I inherited. iDK where they came from.
My sub repair is finished, and re-installed. I wired it for 8 ohms, and glad I did. Brought the bass back to the system, since the factory 4 channel amp to the speakers, cuts the lows with a built in equalizer. That small a sub has limitations, but I do hear it back there.
What is the volume of the box, and the size of the port? To replace the speaker, you need to know those to find the right speaker.

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