I've seen people asking about upgrading to rear disc brakes on this forum for a while now but it seems like no one's tried it. I have a 2012 Civic CNG, which is most similar in trims to the LX. While the front brakes are slightly different, the rears are the same. We can leave the discussion about the merits of doing this for my 110hp car for another thread, but I thought the drums looked ugly and my friends were surprised that a car that MSRPs for $28k would have drum brakes. I studied the DIY on the 8th gen site here:
My step by step drums to disc conversion for Dx and Lx - 8th Generation Honda Civic Forum

It seemed pretty straightforward, so I phoned one of the largest Honda salvage yards in CA (Redline Auto in Rancho Cordova) and purchased the left and right rear spindles, calipers and parking brake lines from a front-end wrecked EX-L. It came out to be about $275 for all those items shipped to LA, which seemed pretty reasonable, compared to the ~$1200 it would be buying everything new. Unless you're swimming in money, I can't recommend paying full price for everything. I already had a set of rear rotors pulled from a 2013 Si from a different project, but you'll probably want to purchase the rotors from the salvage yard as well. The parts came without any of the various bolts, clips, etc, so I used the part diagrams at hondapartsunlimited to order all the fasteners I needed, as well as a new set of brake pads and the brake hoses. I misinterpreted some of the diagrams and ended up ordering a few things I didn't need, but if you're purchasing from a salvage yard, it's anyone's guess as to what will be missing or not. For that reason, I won't post a part list.

I assembled the spindle, rotors, pads/calipers, hoses and parking brake lines before I started, as it's always easier to do this when it's off the car. Be careful when putting the bolts in, I cross-threaded the bolt that holds the parking brake to the spindle and had to retap the hole. The brake lines are side-specific, so be careful when choosing which one you're bolting up. The brake hose mounts as banjo bolt-washer-hose fitting-washer then caliper. If you forget which caliper is which, remember that the drain nut will always face upwards. When mounting the e-brake cable, take note that the base of the metal attachment point has a specific shape to it that needs to be aligned to the hole in the bracket in order to properly put the hose clip in place.

OK, with that out of the way, I decided to approach this in the laziest fashion possible. The service manual states that the proper procedure when removing the rear knuckle of the car is to disassemble the drum brake, which involves removing a lot of stuff I didn't want to bother with. Since I wasn't going to reuse the drum brake, I decided to take the whole thing off with the knuckle and not remove the parking brake cable at all, thus saving me the trouble of opening up the drum. That meant I had to remove the parking brake cables from the front end. To do this, pry up the plastic piece that goes around the gear selector lever then move on to the cup holder. Follow the instructions in this picture. Be careful when removing the bolts in step 1, as the metal under the parking brake lever is very sharp and I cut my finger quite nicely when the bolt broke loose.

When the cables are free, it's time to go under the car. Usual disclaimers apply, if you don't know how to safely get under your car you should definitely research it. Take note of approximately where along the length of the car the center console sits and start looking around there. There's a big aluminum heat shield over the midpipe where the parking brake cables enter the car. It's flimsy, so be careful when working with it. I only had to unbolt one of the sides to be able to reach my hands underneath it to pull the parking brake cables out. There is a rubber grommet that holds each cable in place. The parking brake cables that I got from the salvage yard didn't include this grommet, so I migrated them from the cables I was pulling to the disc brake cables.

Follow the parking brake lines, unbolting the three brackets that hold them in place until you reach the wheel well. Disconnect the brake hose from the line using the small nut at the top, then pull the clip out. Have a catch pan to trap the leaking brake fluid, unless you don't care about it going all over your driveway. The service manual directs you to remove the bracket as well, but I didn't see a reason to do this. Follow the cable for the wheel rotation sensor and unbolt it from the knuckle. There is weather sealing around it, so you'll have to pull harder than you might think to get it out.

At this point, there should be no cables that attach to something else connected to the spindle assembly. While the parking brake cable is dangling around under the car, it's not attached to anything upstream. Get your jack and support the lower arm. Before you start unbolting the knuckle, mark the orientation of the camber plate at the bottom rear position and the camber bolt on the other side of the plate.

The service manual says the correct order for unbolting the knuckle is the top, then the camber adjusting nut, then the one toward the front of car. I saw no reason to do something else, so I went in that order.

The knuckle will start drooping out with the top bolt out. Whatever, take the other two bolts out and remove the knuckle. Then just start going backwards with the disc knuckle. I opted to do the top first because the spindle assembly was about 36 lbs and awkward to hold. Once it was hanging from the upper arm, I was able to pull it down and slide the bottom sections of the knuckle into place on the lower arm. There are guides to slide the bottom sections into the lower arm on the underside of the arm, so you'll be pulling it up into the arm. Reposition the camber plate and bolt in the same orientation they were in when you took them out -- you marked them right? Now raise the jack supporting the lower arm to approximately where the arm would sit under load and tighten all the bolts down. The top bolt is supposed to be at 80lbf/108Nm, the camber nut at 51lbf/69Nm and the remaining flange bolt at 65lbf/88Nm.

Reconnect the brake hose to the brake line, noting that there is a specific orientation that the hose goes into the bracket, then install the clip. Bolt the new parking brake line in the locations the old line was in, then thread the end of the cable into the hole above the midpipe and seat the rubber grommet in place. Go inside the car and attach the end of the parking brake cable to the puller attached the parking brake lever.

Then do the same thing for the other side.

Reinstall the bracket that held the parking brake cables in place. Test the parking brake lever. It's probably not right. Here's how to fix it:

1. Pull the parking brake lever 1 click.

2. Tighten the parking brake adjusting nut until the parking brakes drag slightly when the rear wheels are turned.

3. Release the parking brake lever fully.

4. Check that the parking brakes do not drag when the rear wheels are turned.

5. Readjust if necessary.

6. Make sure the parking brake lever is within the specified number of clicks (8-10).

Reassemble the center console area. Bleed the rear brakes.

The recommendation is to get an alignment done after this, as you have significantly modified a big part of the alignment. That's up to you though.

And that's it! Hope this helped someone.

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