Well, we always have to start off with a disclaimer. A sign of the times I guess. Any thing you decide to do to your braking system is done with no liability to 311s.org or Ed Johnson. Brakes are a serious matter and if you do not feel comfortable working on them, take your car to a reputable brake shop. So why do a rear disc brake conversion on a roadster? This is not for the masses but more for the person that likes to tweak on a car making it better. This might be of real interest to the engine swap crowd. I was not the one who figured this all out. That credit goes to Ed Johnson. And thanks Ed for letting me publish your discovery here. Again, there is nothing wrong with the stock rear brakes. This conversion is just something I had longed to put on my latest project because it can be done. I have yet to actually do the conversion so this write up will change as I personally discover things during the actual conversion.
This conversion is best suited to the dual master cylinder cars. I plan on using a 280Z brake master for my project.
The rear calipers that will work are from a 1982-83 Nissan 200SX. As far as I know they are not left hand/right hand as the Volvo front calipers are. These calipers are pricy new so it is best to go to the local Pick-N-Pull to get your initial setup plus you need other components as detailed below.
So what do we need besides the calipers? Grab the rotors, caliper mounting brackets, and the 200SX emergency brake cabling and hardware that is attached to the 200SX rearend. The caliper mounting brackets are unable to slide off of the 200SX axle until you remove the bearing on the axle. Take a big chisel and a hammer with you when you go to the wrecking yard as there is no sense buying the 200SX rear axle. You do not need it! The 1984 200SX has the correct caliper but it has a IRS and does not have the same mounting bracket.
The 200SX rotor will mount directly onto the roadster axle/hub as the bolt patterns line up perfectly. You may want to change out the studs as detailed below.
The stock caliper mounting brackets for the 200SX have the correct bolt pattern to attach to the axle tube but in the oringinal location the caliper will hit the leaf spring. It is best to have the oringinal mounting holes welded up and then re-drill the mounting holes to tilt the bracket up about 15 degrees for clearance.
Ed used the stock brake line mounting bracket, shortening it to bring the steel brake line closer to the rotor. This was again to clear the leaf springs. New steel brake lines were made using the stock roadster parts but with metric fittings at the caliper to match the fittings of the 200SX brake lines.
The backing plates for the stock drums must be removed and replaced with the retaining bracket we will fabricate per the axle retaining plate drawing. This will require removal and replacement of the wheel bearings, seals, and collar.
The 200SX has 12mm studs versus the 7/16" of the roadster. Ed used the stock studs for the 200SX and drilled the axle to match the slightly larger diameter of the shoulder on the 12mm stud. Of course new wheel nuts to match are required.
Once the caliper bracket holes have been welded up it is easier to cut the center diameter to the larger dimension before cutting away the "end piece" that allows you to install the bracket over the axel tube. Additionally, the shaded area in the drawing of the caliper bracket is milled .125" and the area that is double shaded is radiused where the bracket bends. This provides the proper distance for the rotor to line up in the new caliper.
The caliper bracket is installed on the axel tube and uses the flange on the axle tube for a monting surface. The bolts that retain the axle in the housing come through the retaining plate, the axle housing flange and then the caliper mounting bracket. The caliper bracket only uses only three of the four bolts.
The stock emergency brake cables from the 200SX can be used. It will be necessary to build a bracket to attach to the stock mount on the roadster axle housing. This will enable you to use the stock emergency brake mechanisim on the roadster body.
PDF files of the drawings of the bracket and modifcations can be viewed below:
More will be added as my project comes to life. Thanks again Ed for sharing and thinking out of the box.
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