Upgrading the front brake discs on a Rover 800 from 262mm to 285mm discs
is fortunately a relatively easy job, involving the removal of only 4 bolts
on each side, once the roadwheels are removed. Here is a guide with pictures...
Tools required:
car jack and support stand, ideally one set for each side
3/4" socket for roadwheel
torque wrench
13mm spanner
17mm spanner
17mm socket and ratchet
medium crosshead screwdriver
wood or plastic hammer (possibly)
impact screwdriver (possibly)
white spirit or similar
G-clamp
Step 1: Acquire some caliper carriers suitable for 285mm discs,
some 285mm discs, some new "Loctite'd" caliper guide pin bolts
and some pads for this disc's size.
Step 2: Loosen the roadwheel nuts using a 3/4" socket.
Jack the car up, placing additional support (e.g. an axle
stand) to provide a safe backup in case of jack failure.
Remove the roadwheels.
Note that two 13mm bolts attach the calipers (green arrow) to the
caliper carriers (red arrow), which in turn are bolted to the hub
with two 17mm bolts.
Step 3: Remove the calipers, brake pads, and caliper carriers. Shown
below are a caliper guide pin bolt (13mm - green arrow) and a caliper
carrier-to-hub bolt (17mm - red arrow). Each has a sister bolt which is
out of shot. All must be removed, but remove the calipers before the
carriers. Retain the anti-rattle springs which will most likely fall out
when the brake pads are removed. The caliper guide pins will probably
rotate when you try to remove the bolt. Use a 17mm spanner on them to
stop this (yellow arrow).
An anti-rattle spring...
When the calipers are removed, make sure they are
supported and not left hanging on the brake hose - it can help to
place the roadwheel under the hub for this. Once the calipers and
carriers are removed, the disc can be separated from the hub. It is
held on by two crosshead screws. These are made of a relatively soft
metal compound and if the screws are seized then it is very easy to
damage the screwhead. On occasions an impact screwdriver or
similar may be needed to remove a seized screw, though this is
relatively rare.
Once these screws are removed, the disc can be separated from
the hub. It may be seized and need some persuasion to make it
separate. Do not use a metal hammer, use a wooden or plastic one -
brake discs are made of a brittle metal which can shatter and
cause serious injury from shrapnel.
Step 4: Thoroughly clean the hub mating surface around the four
roadwheel studs and also clean the protective oil layer off the new
discs using petrol, white spirit or similar. Make sure that the disc
inner face which will mate onto the hub is cleaned in this way as
well as the disc friction surfaces, to make sure that any uneven oil
distribution in this area doesn't cause any runout problems.
Now mount the new disc onto the hub making sure that
the counter-sunk screw holes line up with the threaded
holes in the hub.
Press the disc firmly against the hub mating surface and tighten
the crosshead screws to hold it in place.
Step 5: Clean out the caliper guide pin sockets in the new caliper
carriers and fill with a respectable amount of molybdenum disulphide
("moly") high temperature grease. Do not use a copper-based grease
as this will deteriorate to a dry abrasive paste which will cause wear.
Clean the caliper guide pins and insert into the sockets making sure
the small protective gaitors hook over the round metal sealing
lips at each end.
Mount the caliper carriers onto the hub and tighten the bolts to
55lbf ft, 75Nm. Install the anti-rattle springs having bent them
slightly to give the pads a snug fit, then install the pads. The
pad with the built-in metal spring on one end is mounted on
the inner side of the disc.
Step 6: Now partially remove the top on the brake fluid reservoir
(leaving the level detector hanging inside) and use the G-clamp to
press the caliper cylinder back in to be able to accept the new
(thicker) pads. Some advise against doing this, suggesting instead
that the excess brake fluid should be allowed out through the
bleed nipple rather than being pressed back up the line to the
master cylinder. This approach is outside the scope of this
procedure.
Now slide the caliper over the pads to line up with
the caliper guide pin bolts. Mount and tighten the new Loctite'd
bolts using the 13mm spanner, with the 17mm spanner on the
guide pins to stop them rotating. Torque them to 24lbf ft, 33NM.
Anything else left to do?
Ah yes. Remount the roadwheel with the nuts hand tight,
lower the car, and torque the wheelnuts up to 81lbf ft, 110NM.
The procedure is the same for both sides of the car. Remember
to replace the top on the brake fluid reservoir if it was removed
earlier.
Step 7: On the road, apply the brakes a few times before
initially moving away to allow the system to self-calibrate to
the new pads. Avoid harsh braking for the first 200 miles or
so to allow the new discs and pads to bed in.
NOTES
The pads for the two discs sizes are different, subtly.
Surprisingly the 285mm disc pads are slightly smaller than
those for the 262mm discs. Shown here are new Ferodo pads
on the left, compared to the 262mm Halfords pads on the right.
