Some of you were interested in the details of my disc brake conversion, so this is going to be my attempt at a detailed write-up of the project.

Let me start with a disclaimer though: I do not recommend converting to discs this way unless you absolutely cannot source the parts needed to convert to the OEM Volvo disc brakes from the 120 or 1800 series cars. For one thing, there's a fair amount of fabrication involved and it's not a simple matter to get everything precisely the way it needs to be. For another thing, I only know that the brakes work at this point; I have no information on how reliable this conversion will be in the long run.

So now that you've been warned, I will go into the details of the parts used/fabricated and the process involved to make this work.

The project started when I got my hands on some rotors and calipers pulled from a 1995-1996 Nissan 240SX SE (5-lug). The rotors are 252mm diameter and 20mm thick, ventilated. The calipers are single piston floating style, but I don't have much information on them beyond that.



As you can see from the photo above, they clear the original Volvo wheels pretty cleanly.

The next step was to separate the old 1800 hubs (purchased a while back from Belinda) from their rotors. Nothing a good hammer and some carelessness couldn't solve... I pounded the wheel studs out.



After separating the hubs, I took them to a local machine shop and had the outer edges turned down slightly so that it would insert inside the Nissan rotors.

Then I had to get some wheel studs. There was some trouble with this since I needed something with a knurl that fit tightly into the hubs but then stepped down to the same diameter as the threaded portion to slip through the rotor. I could have had the lug-holes on the rotors bored out slightly, but part of the reason for going with the Nissan parts was to easily source replacement parts for wear items like pads and rotors. I ultimately ended up getting some studs with a large knurl diameter, and then using a grinding wheel to grind down the top half-length of the knurl. The studs I chose were 1/2"-20, to match the Ford studs on the rear end. (I'd actually already been using 1/2"-20 lug nuts on the front though. I would have expected that the Volvo studs were metric--and they may be a metric that is just almost identical--but the 1/2"-20 lug nuts fit the Volvo studs.)



Once the studs were sufficiently modified and pounded into place, I had my neighbor weld them to the hub. I chose to weld them in place because after the olds studs had been pounded out, the splines on the hub were barely discernable (probably from the process by which it was secured to the studs), and I didn't want to have a stud start spinning on me some day when I'm trying to change a flat in the pouring rain.

All new bearings, races, and seals.

At this point I could place the hubs and rotors in place to get a feel for clearances and where to position the caliper.









The calipers can fit on the front if angled slightly upward to avoid contact with the steering knuckle. The clearance is very tight, but seems sufficient. To fit the calipers on the back, I would need to move the shocks around to the front side, which (from what I'm told) will create possible interference with the steering unless the lower mounting point is modified.

So now the trick is to fabricate a caliper mounting bracket. Because of the way the spindle and hub are shaped and because of the position of the caliper mounting points, I decided that I could not make the bracket thick enough for my peace-of-mind and also place it between the hub and the spindle. I ended up deciding to use longer bolts and place the bracket on the backside of the spindle. I made a few rough templates out of cardboard, and then one from wood, and then a final copy out of cardboard. I ended up using some fine-thread 3/8" x 1.25" long, grade-8 bolts and nuts for the spindle. The longer bolts I used for the calipers are: class-10.9, 12x1.25, 50mm long.





Then came the real fun... I copied the template onto some 3/8" thick plate steel and cut the basic shape out with a 4.5" angle grinder and a dremel. I used a drill press to drill the mounting holes in the bracket. This is one of those places where it's hard to be perfectly precise. The caliper position holes on the driver's side bracket were rotated slightly lower than I had first intended, so it's slightly closer to the steering knuckle than I had intended, but it still clears everything OK.



You might also note where I ground down the inner portion of the bracket some. This is because the backside of the sprindle is not a simple flat surface. I used some washers to push the bracket slightly off of the curved shape of the spindle, but I also gave the inside some grinding to help clear everything properly.

The last step was to construct a backing plate and splash shield. Once again, I made a cardboard template, and then cut out the shape from some sheet metal. I cut some strips of metal to bridge the gap from the backing plate to the rotor, and had my neighbor weld them around the edges of the backing plate.



In hindsight, I would have designed the splash shield slightly differently, but I think that this one will suffice for a while.

So now let's see the assembly process from the spindle up!





















After that, it was just a matter of bleeding the brakes and going for a test drive.

My assessment is that it is a success. The rears lock up before the fronts now though, so I have ordered a proportioning valve to adjust the brake bias. The brakes actually have a slightly better pedal feel now. (With the drums, it felt like ON/OFF braking with very little modulation through the pedal.) It should also be noted that I am currently using a dual chambered master cylinder from a Chevy, so I don't know what if any difference that has on my braking.


Other notes:

$ The cost of raw materials and parts came to roughly $200 (exlcuding all of the wheel bearing stuff and any tools purchased for doing the fabrication work).

+ $45 - Used calipers and rotors from pick-n-pull junkyard

+ $50 - Used 1800 hubs (Shipping on rotors sucks.)

+ $20 - Machine work on hubs

+ $20 - Wheel studs

+ $10 - Longer bolts (spindle mounting and caliper mounting) and washers

+ $15 - Metal

+ $40 - Brake bias proportioning valve

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 $200 - Total