How To Install 4 Piston Brakes On A 4 Lug FC RX-7

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While the single piston front brakes found on base model RX-7s are excellent, they do have their limitations. High horsepower or track driven cars will quickly exhaust the heat capacity of the smaller rotors. The single piston sliding caliper does not have the precise feel of the fixed 4 piston unit, and the smaller rotor provides far less of a lever on which the caliper can clamp. As the more up market 2nd gen RX-7s (TII, GXL, GTUs, etc.) came with the 4 piston setup it is a common modification to swap the hub and brake setup onto the single piston cars. However, there can be one major disadvantage to this swap; it converts the car from 4 lug wheels to 5 lug wheels. If you are looking to ditch a set of factory 4 lug wheels this may be a bonus for you as it opens up a much wider selection of wheel choices. But what if you found a nice set of 4 lug wheels already and intend to be happy with them for years to come?

In that case, you have probably thought that you are stuck with the smaller single piston brakes. In fact, this is not so. With only a little bit of simple fabrication, the factory 4 piston parts can be made to bolt onto a 4 lug car. The resulting hybrid setup uses factory 5 lug rotors, 4 piston calipers, single piston flex line and of course, the original 4 lug hubs.

Parts Required

• Two 4 Piston 2nd Gen RX-7 Brake Calipers (TII)
• Two 5 Lug 4 Piston 2nd Gen Brake Rotors (TII)
• One Set Of Brake Pads For 4 Piston 2nd Gen RX-7s
• Two Spacers (keep reading)

Instructions

Step 1 - Have The Spacers Made

Your first step is to have a set of spacers made. There is a thickness difference between the 4 lug rotor hat and the 4 piston rotor hat. As it turns out, the 4 lug version is thicker and thus you need to place a spacer between the 4 lug hub and 4 piston rotor to take up that extra slack and allow the rotor to center in the caliper while keeping the wheel base the same.

You can make these spacers yourself, but I highly recommend having them cut at the local machine shop. It is important to keep the hub assembly balanced which may not be possible if using hand tools. A machine shop can inexpensively mill out a set, or if they are so equipped, cut them out on a water jet or laser cutter.

A template is available below as both a JPEG image and a standard DXF file which you should be able to open in any CAD program.

Download Spacer In DXF Format (Zipped, 1K)

The spacer needs to be cut out of 4MM steel. If you need to substitute a size, use the next size smaller.

Step 2 - Remove Single Piston Brakes

Lift the car up and support the front subframe with jack stands. If available, a lift makes this job very easy but jack stands and a driveway works just as well. Before you raise the car, loosen the lug nuts slightly. With the car up in the air, remove both wheels and set them aside. You'll next need to remove all of the single piston brake parts. Break the fluid line loose from the caliper but do not remove it. Remove the caliper retaining bolt and rotate the caliper up. Remove the pads, then slide the caliper off it's pins. At this point you can disconnect the fluid line by rotating the caliper until it unscrews itself. Don't twist the line or you may damage it. Loosen the two large bolts that hold the caliper bracket in place and then remove the assembly from the spindle. You won't need the caliper bracket but you will need the two bolts and lockwashers. Next off is the rotor. It's removed by taking out the two Phillips head screws and then sliding it off of the spindle. Those two screws are often seized in place so if they look like they will give you trouble, drill the suckers out. You won't need them when installing the new rotors anyway. The rotor itself can stick as well so it may require the use of a persuader (hammer).

With the bare hub now exposed, thoroughly clean the surface with a wire brush. A small wire wheel mounted onto a drill works very well. Clean around the wheel studs, around the circumference of the hub and the area where the tapered section (to which the dust cap snaps) meets the rest of the hub. It's important that all junk and corrosion be removed so the new rotor will sit flush.

Step 3 - Redrill the 4 Piston Rotors

From the factory the 4 piston rotors will not fit the 4 lug hub due to the obvious fact that they have different bolt patterns. Thus the 4 piston rotors will need to be redrilled to match the 4 lug hubs.

Place the 4 lug rotor on top of the 4 piston rotor and carefully line them up using the center hub hole. It does not have to be perfect but it should be as close as you can humanly get it. If you have some kind of centering jig available, by all means use it but you can get it very close by simply running your thumb around the inside of the circle, pushing slightly until you no longer feel a ridge where the rotors stack. You're going to want to position the 4 lug rotor so that one of the holes lines up to a corresponding hole on the 4 piston rotor. Set it up so that you end up with the most amount of metal between the factory holes and location of your new hole. It may take a few rotations of the new rotor before you get it right.

Now without disturbing the position of the rotors, center punch the location of the holes on the 4 piston rotor. Just punch the wheel stud holes, don't bother with the small screw holes as they will be of no use.

Now remove the 4 lug rotor. If you are using a hand drill, securely clamp the 4 piston rotor to a work bench and drill out the holes. Use a lot of cutting oil and drill them out in several steps. Start with a 1/8" bit, then go to 1/4", then 3/8" (or 7/16", or whatever size is convenient and close enough). Finally drill out to the finishing size which will be 9/16" (14.2MM). You will need a powerful drill and a good set of bits to do this. Don't bother trying to use that 9.6V cordless drill, you need an 18V beast or something with a cord. Keep the speed slow and lubricate well with cutting oil. If you have a drill press, you can probably drill out 1/4" and go right to 9/16" without taking all the intermediate steps. Deburr the new holes both front and back.

The rotor should now fit over the 4 lug hub and remain centered due to the hub centric center hole. While test fitting you will find that the rotor scrapes the dust shield. Don't worry about this for now.

Step 4 - Trim The Dust Shield

Hopefully your 4 lug 4 piston spacers have now returned from the machine shop, because we'll need them in the next step. But for now, we need to deal with the dust shield. The much larger 4 piston rotor wants to occupy the same space the smaller 4 lug dust shield currently exists in. As no two objects may occupy the same space at the same time (in the same dimension anyway), one of them must go. There are two choices here. The first and easiest is to just cut away the lip on the 4 lug dust shield. This leaves much of the dust shield in tact to protect the rear of the rotor but eliminates the clearance issue. If this is the approach you want to take, then simply use a cutting wheel or Sawzall to cut the shield, following the fold line around its circumference. The deburr with a file.

The second approach, and perhaps the more elegant one, is to swap on the 4 piston dust shield. They are available at the dealer as parts FB05-33-260B (right) and FB05-33-270B (left). However removal and replacement of the shield involves removing the hub, and thus needing to service the bearing at the same time. If you bearings and bad then you might as well replace the dust shield as you will be removing the hub anyway.

The choice is up to you. However it is worth mentioning that most track cars don't use the dust shield in favor of more airflow and thus better brake cooling.

Step 5 - Prepare And Install Spacers

If you've already tried your spacers on the 4 lug hub, you already know they don't fit. If you have not tried your spacers on the 4 lug hub, try them and they won't fit. As you can probably tell, the hub center is tapered where it means the flange. The spacer, having a 90 degree lip, won't fit over the taper. To correct this, mount the spacer in a good vice and then use a grinder to grind a bevel onto the underside of the inner hole. You'll need to cut down about 2.5MM to make it fit. Test your fitment several times during the process to make sure not to over grind. Do not grind away at the inner radius of the spacer. That hole must remain true for the spacer to center on the hub. If you start grinding it out, the spacer will not center itself and you may end up with vibration.

When the spacer is ground enough to fit flush against the hub, coat the hub side with a generous helping of anti-seize and then place it over the wheel studs onto the hub. Repeat for the other side.

Step 6 - Install The Rotors

Coat either the top side of the spacers (don't forget the edges) or the underside of the rotor hat with plenty of anti-seize and then install the 4 piston rotors. If all is well the rotor will fit snugly against the center of the hub and remain centered. Use two lug nuts to hold the rotor in place for the next few steps. Repeat for the other wheel.

It's a good idea to use a bit of caliper paint on the exposed areas of the rotor hat so they don't rust up the first time it rains. Nothing is more ugly then an exposed set of rusty rotors under a great set of wheels.

Step 7 - Install The Calipers and Pads

Now it's time for the fun stuff. To prepare for caliper installation, clean up the two large bolts that held the single piston caliper bracket to the spindle with a wire brush or wire wheel. Make sure the threads are clean. Shoot some brake cleaner through the threads on the spindle as well and clean with a brush if you have one small enough to fit. Wash down the rotors with brake cleaner to remove all grease and oil that may have found its way onto the surface during handling and installation.

Clean all the gunk that may have accumulated on the brake flex line fitting with a rag and some brake cleaner. Put a small dab of anti-seize on the threads of the fitting, making sure not to get any onto the flared sealing surface (you don't want it to end up in the caliper). Holding the flex line stationary, spin the caliper onto the line until snug. Now tighten it up with a flare nut wrench (10MM). If you find that you must twist this line to install the caliper, you're going to have to remove the line from the car and let it hang free during caliper installation. Then reconnect it to the car once the caliper is in its final orientation.

With the line attached, place the caliper onto the hub with the brake bleeder at the top and line up the bolt holes. Those who have done a brake job on a factory 4 piston car are probably wondering where the caliper shim is. It's not used in this setup. With anti-seize on the threads, install and snug up the caliper bolts. Once both bolts are installed and the caliper is held in place, torque to 58-72 Ft-LBs. The rotor will sit a bit closer to the outside of the caliper then the inside. This is normal due to the width of the spacer (and why I say to go thinner on the spacer rather then thicker if you can't find 4MM stock) and will not effect operation of the brakes or pad wear.

Now insert the pads. Put anti-squeal goo on the backside of the pads and both sides of the shims, then insert into the caliper. Coat the guide pins in brake lube and push them through the caliper and pads so that the end with the hole faces the back of the caliper (note the picture is taken with the pins installed backwards so you may see how they are installed). Install the bare metal pin retaining spring through the holes in the back of the pins. Finally, install the blue pad spring as shown. It hooks around the bottom most pin and into the caliper.

Repeat for the other wheel.

Painting the caliper really improves its appearance. Caliper enamel is available at most auto parts stores and is formulated to resist heat and brake fluid. I prefer to use VHT brand. When you paint, make absolutely sure that the caliper is perfectly clean first and make sure to cover the fluid connection.

Step 8 - Bleed The Brakes

Bleed the brakes according to the procedure in the Factory Service Manual. Start at the farthest wheel, which is the right rear. Then move onto the left rear, then the right front, and finally the left front. You will find that the 4 piston calipers hold a hell of a lot of air. It may take several attempts to get all of the air out. I find that the first time they are bled, it's useful just to leave the bleeder wide open and pump the pedal until most of the air is gone. Then close the bleeder and start the normal bleeding procedure. Make sure to keep the master cylinder topped off or you're going to have to start all over again.

Step 9 - Reinstall The Wheels

Remove your temporary lug nuts and then clean the threads of the wheel studs. Coat the wheel studs with anti-seize as well as the mating surface of the brake rotor. Slip the wheel over the studs and then snug down the lugs in a criss cross pattern. Repeat for the other side then lower the car. Now torque the wheels in a criss cross pattern to 90 FT-LBs.

Step 10 - Test The Brakes

In the car, pump the pedal and make sure the brakes hold pressure. If they hold and the pedal does not sink to the floor, go for a short test drive. Proceed carefully and avoid any busy streets until you are sure the brakes are functional. This is probably the point at which you will find out you need to bleed them more. The 4 piston calipers will hold a lot of air bubbles which will appear out of nowhere the first time you drive the car. So don't just go full throttle down the street and slam on the brakes expecting them to be 100%! If you need to rebleed, do so before driving further. If the brakes are working as they should, make a series of stops, each slightly harder then the last. This will bed in the pads and rotors. Over the next few days, pay careful attention to the feel of the brake pedal and investigate any changes immediately.

Notes

1. Since you'll have the brakes apart, now is probably a good time to service the bearings. Additionally if you want to upgrade the brake lines, it's convenient at this point. Braided stainless will generally look a lot better and give you slightly better pedal feel. Make sure to buy DOT approved lines.

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