I have two '94 960 wagons, and I have been less than satisfied with the pulsations during braking that are more or less notable on the two cars. Over the years of browsing this board for clues and answers, I have seen various possible causes, most of which allude to warped rotors or front control arm bushings.

These are true and reasonable clues, but the real culprit is the design itself. In particular, the fact that the braking force of the front brakes is transmitted directly to the car body through the contol arm in compressive force. This direct transmission of the braking force straight through the axis of the control arm makes for a harsh transmission of road shock and any uneven forces of the pads/caliper and rotor. The requirements of measured runout at the rotor are quite stringent to minimize any pulsations.

My previous experience with maintaining our cars has been with older Mercedes and the whole front axle design is completely different there, with the engine mounted directly to the front axle and the body sitting on top of the front axle with rubber "subframe mounts". In the Mercedes design, measured runout of 0.003 inch or less is no problem at all; you never feel any uneven braking or harsh road shock.

With the Volvo design that I have, measured runout of even 0.0005 inch can be just barely discernable as pulsation in some conditions. Almost a factor of ten smaller runout, and I use only the Volvo pads.

This leads me to the conclusion that to do the brakes right or well when you replace the pads on this design requires that you have an indicator and somthing like a magnetic base to hold it to enable you to measure the rotor runout.

After you take the caliper off the wheel mount, mark the hub & rotor positioning so you know how they were lined up before. Then take the rotor off the hub & clean both the mating faces of the hub & the rotor as absolutely best as possible (wire brush & steel wool). While you're there, you can also clean out the wheel sensor magnet which was flocked with little steel hairs on mine & the brake dust off the hub. Then comes the indicating of runout. I started with the original position and tried several others of the five possible positions. At each, you make sure that there is not any dust or anything on the mating surfaces of rotor or hub, then carefully push it straight on and put three lug nuts on, snugged without moving the rotor. Then indicate the runout near the center track of the brake pad. Hopefully you can find a postion that gives 0.0005 inch or less.

Interestingly enough, on the side that I got to 0.0005, before I took the rotor off and cleaned everything as I cited above, the runout was ~0.0015 in the same position as I had taken it off, which was the best possible position that I found on the hub.

Recently someone posted a link to a site that had some excerpts from several Volvo 'Green' manuals. Among these was some out of the brake manual for the 760 series that I believe has the same front suspension design as my '94 960. In it was shown a machine for double-disk grinding the rotors ON THE HUB. I had never seen this before, but now I know why they showed it in there; because this design really IS that sensitive to runout.

Now that I've fixed one of these 960's, I'll fix the other one in a week or two. I remember when I did the brakes some time ago, I did indicate the rotor runout to be ~0.0014 and thought at the time "this can't be it". . . Now I know better.