Honda Civic Rear Drum-to-Disc Brake Conversion

Most builders pull the rear disc setup from a junkyard car. Suitable donors include the 99-00 Civic Si, any 94-01 Integra, and the Del Sol. Owners report that trailing-arm and parking-brake-cable lengths match across the 88-91 and 92-95 Civics as well as the 90-93 and 94-01 Integras, so donor choice is flexible. Decide up front between two methods: transplanting the complete trailing arm (simplest, and it bolts directly to the Civic chassis), or moving only the hub and brake assembly onto your existing arm. The hub-only route skips the need for a rear alignment, but the retaining fasteners are Torx T50 and will strip if a hex key is used by mistake. Junkyard arms usually arrive with the cables and lines already cut, so plan on fresh parking-brake cables. Inspect the bushings and replace them before installing the arm; note that some Integra bushings are physically larger than Civic ones, so confirm any polyurethane kit matches the arm you actually have.

To free the donor rotors for inspection, remove the two 10mm bolts holding each heat shield, then unbolt the caliper (two 12mm) and the caliper bracket (two 14mm). Back out the two disc retaining screws with a hand impact driver rather than a plain screwdriver, which almost always strips the shallow heads. Have the rotors measured and turned to confirm they remain within minimum-thickness spec. If they are already too thin to machine, replacement is inexpensive: a plain set runs about $66, while slotted performance rotors run near $99 and improve bite. Wipe the caliper and hub down with brake cleaner to clear any grit that could later cause the pads to bind or drag.

Chock the front wheels, lift the rear of the car, and set it securely on jack stands; placing all four corners on stands makes the later bleed far easier. Remove the rear wheels. Purge the old fluid from the rear side by fitting a hose to one bleeder screw, opening it, and pumping the pedal with the master-cylinder cap removed until the line runs dry into a catch container.

Confirm the parking brake is fully released. Inside the cabin, take out the six Phillips screws securing the center armrest and lift it off toward the rear. Back off the cable adjuster to create slack, then detach the cables from the handle. Remove the two bolts anchoring the cables, pull the rear carpet back, and press the two rubber grommets down through the floor holes where the cables enter.

Position a jack under the lower control arm so nothing drops onto you when the fasteners release. Separate the rear brake line where it joins the hard line by unthreading the fitting and pulling its retaining clip. Then remove the arm's mounting fasteners in turn: the compensator link at the chassis (one 10mm), the two 12mm bolts through the main bushing at the chassis, the 10mm where the lower control arm meets the arm, the 10mm where the shock ties into the lower control arm, and the 10mm at the upper control arm. Lower the jack and set the old arm aside. Soaking every fastener with penetrating oil the day before pays off here: the main frame bolts thread into nuts welded inside the frame and can shear or spin their welds loose, a failure that is very difficult to recover from.

Clear the leftover hardware from the donor unit. Remove the old parking-brake cable by undoing the one or two bolts holding it to the arm, releasing the clip where it passes through its bracket, and pulling the retaining clip off the pin at the caliper end. Keep that clip and pin. Unthread the banjo bolt to detach the old brake line, catching both sealing washers. Route the new parking-brake cable through the arm exactly as the original sat, passing it over the fuel-tank strap rather than beneath it, and press its rubber grommet firmly into the chassis opening.

Set the rotor onto the hub and lightly snug its two retaining screws with a Phillips driver; they only need to be set, not torqued. Reattach the caliper bracket. Prepare the pads by coating the pad side of each shim with brake-quiet spray, letting it tack up for a minute or two, then seating the shim against the pad backing. The pad carrying the metal wear-indicator tab installs on the inboard side, behind the rotor.

Retract the piston before mounting the caliper. Seat a flat-blade screwdriver in the cross slot on the piston face and turn clockwise so the piston screws inward. Watch the rubber boot; if it begins to twist or bind, stop, mist it with brake cleaner, and resume. Stop once the piston sits nearly flush with the boot, and leave one of its slots facing down so the locating nub on the pad drops into it. Mount the caliper onto its bracket, keeping any old fluid off the rotor face.

Rest the assembled arm on a jack and raise it into position. Reverse the removal order: start the upper control arm bolt first, then the shock bolt and the lower-control-arm bolt. Set the compensator link bolt at roughly its original position, using the clean, unrusted band on the shaft as a reference for where it sat. Install the two bolts tying the arm to the chassis. Feed the parking-brake cable through the arm, passing it through the forward hole with the rubber stop resting in the second hole, secure the mounting brackets, then connect the cable end at the caliper with its pin and clip.

Bolt the rear brake line's bracket to the mount on the trailing arm, then attach the line to the caliper over clean banjo washers, replacing any that look damaged. If you are running steel braided lines, they secure with a threaded retaining bolt instead of the stock clip. Install speed bleeders now if you are using them, threading each in until hand-snug. Repeat the caliper, pad, and line work on the opposite side.

Change the proportioning valve for one matched to rear discs. Note the port arrangement before disconnecting the lines so they reconnect correctly, then remove the two mounting bolts; the lower bolt can be difficult to restart, and it may be left out if access is impossible, since the valve barely moves. A Civic Si valve is the usual choice; some builds instead run an earlier Integra valve marked 4040 (two inlets, four outlets). On any non-EX chassis with stock or soft suspension, also fit the correct master cylinder: the Si unit is 15/16. Leaving the stock rear-drum brake bias in place can over-apply the rear discs and lock the wheels under braking, especially mid-corner. On EX models the bore is close enough that the swap is optional, and cars on stiffer, lowered suspension often brake fine on the stock valve.

Top the reservoir with fresh fluid, then bleed each caliper in turn. Open a bleeder about one to two turns, run a hose from it into a container set above the screw so bubbles are easy to see, and pump the pedal while watching the fluid. Refill the reservoir every ten to fifteen pumps so it never runs low and draws in air. Without speed bleeders, leave enough fluid in the catch bottle to submerge the hose end, forming a one-way seal while a helper pumps. Close each bleeder once the stream is bubble-free and move to the next. Finish with the reservoir at the max line and refit the cap, then reinstall both rear heat shields with their 10mm bolts.

Refit the wheels and lower the car. Reconnect the parking-brake cable ends as they came off and reinstall both anchor bolts; the center screw is the adjuster. Tighten it until the handle locks fully at roughly six to ten clicks. To fine-tune with the car on stands, spin a rear wheel, pull the handle one click, and adjust until you feel light drag, then release; the wheel should turn freely again. Recheck the adjustment after a couple of weeks once the pads and rotors have bedded in.

Check the parking brake first: set it with the transmission in neutral and try to push or roll the car, which it should hold. Then take a cautious test drive, braking gently at about 10 mph and again at 25-30 mph. The pedal will feel different from drums; a soft or spongy pedal means air remains in the lines, so bleed again before driving the car normally.