Vehicle Damage Warnings

BRAKE LINES & LININGS
Remove one of the front wheels and inspect the brake disc, caliper and linings. (The wheel bearings should be inspected at this time and repacked if necessary.)
Do not get any oil or grease on the linings. It is recommended that both front wheel sets be replaced whenever a respective shoe and lining is worn or damaged. Inspect and, if necessary, replace rear brake linings also.
If the caliper is cracked or fluid leakage through the casting is evident, it must be replaced as a unit.

BRAKE ROUGHNESS
The most common cause of brake chatter on disc brakes is a variation in thickness of the disc. If roughness or vibration is encountered during highway operation or if pedal pumping is experienced at low speeds, the disc may have excessive thickness variation. To check for this condition, measure the disc at 12 points with a micrometer at a radius approximately one inch from edge of disc. If thickness measurements vary more than specifications allow, the disc should be replaced with a new one
. Excessive lateral runout of braking disc may cause a ``knocking back'' of the pistons, possibly creating increased pedal travel and vibration when brakes are applied.
Before checking the runout, wheel bearings should be adjusted. Be sure to make the adjustment according to the recommendations given in the individual truck chapters.

BRAKE DISC SERVICE
Servicing of disc brakes is extremely critical due to the close tolerances required in machining the brake disc to insure proper brake operation.
The maintenance of these close controls on the friction surfaces is necessary to prevent brake roughness. In addition, the surface finish must be non-directional and maintained at a micro-inch finish. This close control of the rubbing surface finish is necessary to avoid pulls and erratic performance and promote long lining life and equal lining wear of both left and right brakes.
In light of the foregoing remarks, refinishing of the rubbing surfaces should not be attempted unless precision equipment, capable of measuring in micro-inches is available.
To check runout of a disc, mount a dial indicator on a convenient part (steering knuckle, tie rod, disc brake caliper housing) so that the plunger of the dial indicator contacts the disc at a point one inch from the outer edge. If the total indicated runout exceeds specifications, install a new disc.

GENERAL PRECAUTIONS
1. Grease or any other foreign material must be kept off the caliper, surfaces of the disc and external surfaces of the hub, during service procedures. Handling the brake disc and caliper should be done in a way to avoid deformation of the disc and nicking or scratching brake linings.
2. If inspection reveals rubber piston seals are worn or damaged, they should be replaced immediately.
3. During removal and installation of a wheel assembly, exercise care so as not to interfere with or damage the caliper splash shield, the bleeder screw or the transfer tube (if equipped).
4. Front wheel bearings should be adjusted to specifications.
5. Be sure vehicle is centered on hoist before servicing any of the front end components to avoid bending or damaging the disc splash shield on full right or left wheel turns.
6. Before the vehicle is moved after any brake service work, be sure to obtain a firm brake pedal.
7. The assembly bolts of the two caliper housings (if equipped) should not be disturbed unless the caliper requires service.

INSPECTION OF CALIPER
Should it become necessary to remove the caliper for installation of new parts, clean all parts in alcohol, wipe dry using lint-free cloths. Using an air hose, blow out drilled passages and bores. Check dust boots for punctures or tears. If punctures or tears are evident, new boots should be installed upon reassembly.
Inspect piston bores in both housings for scoring or pitting. Bores that show light scratches or corrosion can usually be cleaned with crocus cloth. However, bores that have deep scratches or scoring may be honed, provided the diameter of the bore is not increased more than .002 inch. If the bore does not clean up within this specification, a new caliper housing should be installed (black stains on the bore walls are caused by piston seals and will do no harm).
When using a hone, be sure to install the hone baffle before honing bore. The baffle is used to protect the hone stones from damage. Use extreme care in cleaning the caliper after honing. Remove all dust and grit by flushing the caliper with alcohol. Wipe dry with clean lint-free cloth and then clean a second time in the same manner.

BLEEDING DISC BRAKES
The disc brake hydraulic system can be bled manually or with pressure bleeding equipment. On vehicles with disc brakes the brake pedal will require more pumping and frequent checking of fluid level in master cylinder during bleeding operation.
Never use brake fluid that has been drained from hydraulic system when bleeding the brakes. Be sure the disc brake pistons are returned to their normal positions and that the shoe and lining assemblies are properly seated. Before driving the vehicle, check brake operation to be sure that a firm pedal has been obtained.