Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

Rotors:
Brake Rotor Replacement
Front Brake Rotor Replacement.
Does the Brake Rotor Need Replacement? I have just replaced the front pads on my 740. When I was
changing out the pads I noticed that the rotors had a lip around the outer edge. The metal sticks out approx.
1/16 inch beyond the rest of the rotor. This is the area above where the pads normally contact the rotor. The
rotors do not seem to be warped. Should grind this outer edge off so that the entire rotor is of uniform
thickness? Does this mean that the rotors are worn down too much and therefore I need to replace them?
My new pads seem like they are too loose in the calipers. [Suggestions:] Regarding the lip, you don't really
need to worry about this, unless the pads are riding on the lip. But, it sounds like it's time for new discs. If
memory serves me right, new thickness of a ventilated disc is 22mm, min thickness is 20mm (for a solid disc
this is 14 and 11.5mm, respectively) so if you have 1/16 inch lip on each side, that's 1/8 which is 3mm, so
that'd put you at 19mm. How much can only be determined by measuring them with a micrometer and
comparing measurements with minimum standards.
Replacing the Rotors. Changing the rotors is very easy. With wheel off, remove the caliper (2 -13mm bolts)
and hang it up with a wire so it does not strain the brake hoses. Then remove the caliper mounting bracket
by removing the two 10mm allen or Torx-style bolts. If the latter, use a 3/8 drive or larger socket as they tend
to be difficult to turn. Unscrew the wheel locator index pin. Whack the rotor a few times with a mallet to
loosen it and pull off rotor. [Tom Irwin] Hit the hubs with a wire cup brush chucked in a drill motor, cleaning
off all corrosion everywhere the rotor mates with the hub. To avoid mismatch and subsequent vibration, the
hubs must be shiny clean EVERYWHERE that the rotors touch, even around the wheel studs. Wipe the new
rotor with solvent-based brake cleaner to remove its protective oil coating, Then replace the rotor, the caliper
mount, and the caliper. When reinstalling the wheel, see Anti-Corrosion Advice for tips on preventing stuck
wheel bolts and wheels. [Editor] While the manual suggests that you use new brake caliper mounting bolts,
general consensus is that this is unnecessary. They can sometimes stretch causing them to come into
contact with the inboard rotor surface. For peace of mind, use Loctite on the bolts when reinstalling.
Brake Rotor Identification. [Tip from Larry Jacobson] When I bought front disks for my '91 744T the Volvo
dealer said there are three disks that are stock on that car and they all look the same. The only surefire way
to get the right disk is to tell them the *exact* diameter and then they can match the part. When disks are
bought from an aftermarket source it's a crapshoot unless you haul in the old part and carefully compare it to
the new part.
Brake Rotor Balance. [Editor] See the note below to match the balance lines on rotor and hub and minimize
runout.
Brake Rotors: Premium versus Economy. [Tips from Counterman Magazine, August 2001] What's the
difference between "economy" rotors and "premium" rotors? Besides price, there are also differences in
rotor quality, performance, fit and finish. Premium rotors typically follow the design of OEM rotors because
rotors are engineered to meet certain noise, cooling, friction and performance characteristics. If a
replacement rotor does not meet the OEM criteria, it may take the brake system out of compliance with
FMVSS105 or FMVSS135 government safety standards.
Economy rotors may not meet these requirements and may decrease braking effectiveness and increase
pad wear. Because of this, some suppliers of premium rotors now "certify" their rotors as meeting all OEM
requirements. One reason for these differences is the metallurgy of the rotors. Economy rotors are typically