By Glenn Goodspeed (November, 1992)
If you have an early 1800 with a pre-7000 chassis number, you may have discovered already that front brake rotors are no longer available new from Volvo. As far as I can tell, they are no longer available from any source. So what do you do if you want new rotors? One option is to convert to later model brakes.
This is easier than you might think. You need a few parts from a later model car, and a pair of new rotors from Volvo. Calipers are interchangeable from early to mid-production, and they are the same on Volvo 122s as they are on 1800s.
The newer rotors are a little bit shorter than the old ones, and the caliper mounting blocks are shorter to adjust the placement of the calipers. The new mounting blocks are threaded differently, and thus require different caliper mounting bolts.
The only other parts you'll need will be a pair of brake disc backing plates from a later model car. There are a few different styles, but I believe they will all work except, of course, the early ones that came on your car. To be sure you get the parts you need, tell your supplier you want replacement parts for a '65 or '66 1800. Some suppliers are easily confused by chassis numbers and indeed by any knowledge superior to their own.
Boston Volvo, for instance, although my favorite supplier of stock parts, apparently does not understand that the rotor they sell new for the '65 1800 includes the hub and wheel bearing races. In fact, I specifically asked if the part was a hub-and-rotor assembly, and was told that it was just a rotor.
On the strength of this information and the $80 price, I decided to shop around. Big mistake. I ordered a pair of aftermarket rotors without hubs for $60 apiece. When they arrived, I compared them with the ones on the car, and realized that I would need some other parts to make them fit. I wasn't sure exactly which parts I needed, and I called the supplier, who sent me a pair of caliper mounting blocks and a pair of hubs.
Thinking I had everything I needed, I proceeded to remove the old brakes and replace the rotors. When I got the new rotors on the hubs and mounted on the spindles, I checked the runout as a matter of course. It measured far more than Volvo specs, so I made some more measurements, and discovered that the rotors I had purchased were only 12.2mm thick, compared the Volvo spec 12.6mm for new rotors.
What bothered me more was the minimum thickness stamped on the side of the rotor: 11.3mm. Volvo specifies a minimum thickness of 12.2mm. Now I knew that the rotors were not manufactured for use on a Volvo 1800, but I felt I had done too much work already to abandon the project. This was another big mistake, as I discovered later that without the caliper bolts and the backing plates, I couldn't finish the job anyway.
I decided to have the hub-and-rotor assemblies machined to cure the runout problem, and just run the car with thin rotors. Then things got really strange. When I brought them back from the machine shop, the rotors had almost as much runout as when I brought them in. Thinking that the shop had not cut enough off of them, I brought them back and watched carefully as they re-cut the discs. Back at home, the discs displayed just as much runout as before. By now, they were much too thin to re-cut, and I was convinced that there was more to this than met the eye.
After thinking about all the possibilities, I concluded that the bolt circle on the rotor did not match that on the hub. This placed uneven stress on the rotor that caused it to warp when it cooled off after being machined. Of course the supplier blamed the machine shop, and said that no one else had had any trouble with his rotors.
I ordered new rotors from Boston Volvo, and was pleasantly surprised when they arrived complete with hubs and bearing races installed. The runout on both was well within specs, and, armed with all the proper parts for the conversion, I completed the job in one leisurely day.