|Home||Diplomat Info||Registry||Upgrades||Photos||Links||Farley||Site Tools||Manual||Forum|
Brake Hose and Tubing
Cleaning and Inspection
Removing Caliper from Vehicle
The disc brake assembly includes a braking disc, splash shield, adapter and caliper assembly with inboard and outboard shoe assemblies.
One type of caliper assembly is used on all models. A single piston and a lateral moving caliper assembly produces clamping action to force both shoes against the sides of the disc.
Sliding Caliper brakes have two machined abutments on the adapter to position and align the caliper. Two retainer clips keep the caliper in the machined guides or �ways� on the adapter and allow lateral movement of the caliper (Figs. 1 and 2). The outboard shoe is flanged (Fig. 2) to radially locate and position the shoe on the caliper fingers. All braking force on this shoe is taken by the caliper. The inboard shoe is held in position by the adapter (Fig. 7) and reacts directly on the adapter.
The caliper is a one piece casting with the inboard side containing the single piston cylinder bore. The piston is plastic. A square cut rubber piston seal is located in a machined groove in the cylinder bore and provides a hydraulic seal between the piston and the cylinder wall. A moulded rubber dust boot installed in a counterbore in the cylinder bore and a groove in the piston keeps contamination from the cylinder wall and piston.
As the brake pedal is depressed, hydraulic pressure is applied against the piston. This force is transmitted to the inboard shoe and the inboard braking surface of the disc. As force increases against the disc, the caliper assembly moves inboard pulling the outer shoe against the outer surface of the disc. Thus, providing a clamping force (Fig. 3).
When the brake pressure is released, the piston seal (distorted by applied pressure) (Fig. 4) returns to its normal position providing clearance between the inboard shoe and disc. Disc runout and piston seal deflection provides outboard shoe clearance.
Automatic adjustment is obtained by outward relocation of the piston as the inboard lining wears and the inward movement of the caliper as the outboard lining wears. The piston caliper movement maintains correct adjustment at all times.
Check Brake Lines, Hoses and Linings
Raise all four wheels. Remove wheel and tire assemblies and inspect the braking disc, linings and caliper. Inspect brake flexible hose and tubing according to procedure outlined in paragraph entitled �Brake Hose and Tubing� (The front wheel bearings should be inspected at this time and repacked if necessary). The caliper assembly must be removed in order to inspect the inner wheel bearings. (Refer to �Brake Shoe Removal� paragraph).
Do not get oil or grease on the braking disc or linings. If the linings (pads) are worn to within 1/8 inch of the shoe, replace both shoe assemblies, (inboard and outboard) on the front wheels. It is necessary that both front wheel sets be replaced whenever shoe assemblies on either side are replaced.
Check all brake tube connections for possible leaks. Install new hoses as required.
Check adapter plate to knuckle bolts for specified torque.
Shoe and Lining Wear
If a visual inspection does not adequately determine the condition of the lining, a physical check will be necessary. (Outboard shoes are originally thinner than inboard shoe). To check the amount of lining wear, remove the wheel and tire assemblies, and the calipers. Remove the shoe assemblies (See �Brake Shoe Removal� paragraph). Combined shoe and lining assembly thickness should be measured at the thinnest part of each shoe and lining assembly. When an assembly is worn to approximately 5/16 inch, both inner and outer shoe assemblies should be replaced on both front wheels. (See �Brake Shoe Removal� paragraph). It is normal for the inboard lining to show slightly more wear than the outboard.
BRAKE HOSE AND TUBING (back to CONTENTS)
Inspection of brake hose and tubing should be included in all brake service operations and every second oil change (every oil change for vehicles used in fleet service; Police, Taxi, etc.). The hoses should be checked for:
(1) Correct length, severe surface cracking, pulling scuffing or worn spots. (If the outer casing of the hose has severe cracks or abrasions, the hose should be replaced). Eventual deterioration of the hose can take place with possible burst failure.
(2) Faulty installation to cause twisting, wheel, tire or chassis interference.
Always use factory recommended hoses to insure quality, correct length and superior fatigue life. Care should be taken to make sure that the tube and hose mating surfaces are clean and free from nicks and burrs. New seal washer(s) should be used and all connections should be properly made and tightened. Double wall steel tubing should always be used for replacement. Care should be taken when replacing brake tubing, to use the proper bending and flaring tools and to avoid kinking, routing the tubes against sharp edges, moving components or in hot areas. All tubes should be properly attached with recommended retaining clips.
(1) Check the master cylinder fluid level at each lubrication period. Maintain fluid level to bottom of rings in the reservoir. Use only clean brake fluid conforming to
(2) Linings should maintain light contact with the disc or have no more than .005 inch clearance. However, if the vehicle was braked to a stop shortly before checking clearance, it is normal for the brakes to drag. If the linings are more than .005 inch from the disc, apply the brakes several times and recheck the clearance.
(3) �Knock-back� of the linings can be caused by the normal deflection of front suspension components during a hard turn. In effect, the disc is tilted and knocks the linings and pistons back. Excessive running clearance results and the driver will notice increased pedal travel on the next brake application. Loose or worn suspension parts, especially from wheel bearings, can increase the problem and cause the driver to pump the pedal several times to get braking action. Check and adjust or replace loose, worn or broken parts.
(4) Check lining wear at least every 10,000 miles under normal operating conditions. If operating conditions are severe, lining wear should be checked more frequently.
(5) Lack of parallelism between the two faces
of the disc, (variations in disc thickness) may cause excessive pedal travel, front end vibration, or a pumping (up-and-down movement) of the brake pedal when braking a moving vehicle. Check disc thickness if these symptoms are present.
(6) Disc lateral runout is �wobble� from side to side and can cause linings and pistons to be �knocked back� causing increased pedal travel. If the disc wobbles slightly when rotated, even though the wheel bearings are in good condition and properly adjusted, the wobble will usually not affect braking efficiency. Disc lateral runout should be checked whenever major service procedures are required on a disc brake system.
SERVICE PROCEDURES (back to CONTENTS)
BRAKE SHOES (back to CONTENTS)
(1) Raise vehicle on a hoist or jackstands.
(2) Remove front wheel covers, and wheel and tire assemblies.
(3) Remove caliper retaining clips and antirattle springs (Fig. 5).
(4) Remove caliper from disc by slowly sliding caliper assembly out and away from disc.
(5) Remove outboard shoe assembly (flanges on outboard shoe will retain shoe to caliper) by prying between shoe and caliper fingers (Fig. 6). Support caliper so as not to damage flexible brake hose. Remove inboard shoe assembly (Fig. 7). Do not let caliper hang on hose.
Cleaning and Inspection
Check for piston seal leaks (evident by brake fluid in and around boot area and inboard lining) and for any ruptures of piston dust boot. (Fig. 8). If boot is damaged, or fluid is evident, it will be necessary to disassemble caliper assembly and install a new seal, boot, (and piston if damaged or corroded.) (Refer to �Disassembling Caliper Assembly� paragraph). Check the mating surfaces of the abutments on the caliper and adapter. If corroded or rusty, remove �0� ring around adapter. �Ways� (Figs. 7 and 8) clean surfaces with wire brush, reinstall �0� ring Inspect braking surfaces of disc.
(1) Slowly and carefully push piston back into bore until it is bottomed. Watch for possible master cylinder reservoir overflow.
(2) Slide new outboard shoe assembly in recess of caliper, after removing the protective paper from the noise suppression gasket. CAUTION: No free play between brake shoe flanges and caliper fingers (Fig. 9) should exist (which might cause brake shoe rattle). If free play is evident by vertical shoe movement after installation, remove shoe from caliper and bend flanges (Fig. 10) to create a slight interference fit to eliminate all vertical free play when shoe is installed. Install shoe after above modification, if necessary, by snapping shoe into place with fingers or with light �C� clamp, protect new lining from damage or contamination by using old shoes over new lining and across caliper fingers (Fig. 11).
(3) Remove the protective paper from the noise suppression gasket and then position the inboard shoe in position on adapter with shoe �flanges� in the adapter �ways� (Fig. 7).
(4) Slowly slide caliper assembly into position in adapter and over disc. Align caliper on machined ways of adapter. BE CAREFUL NOT TO PULL THE DUST BOOT FROM ITS GROOVE AS THE PISTON AND BOOT SLIDE OVER THE INBOARD SHOE.
(5) Install anti-rattle springs and retaining clips and tighten retaining screws to 180 in. lbs. (20 N�m). The inboard shoe anti-rattle spring must always be installed on top of the retainer spring plate. (Fig. 1).
(6) Pump brake pedal several times until a firm pedal has been obtained.
(7) Check and refill master cylinder reservoirs (if necessary) with DOT 3 brake fluid as required. It should not be necessary to bleed the system after shoe removal and installation. However, if a firm pedal cannot be obtained, bleed the brake system as described �Bleeding the Brake System� paragraph. It may have been necessary to remove fluid to put in new linings as fluid is pushed back into the master cylinder.
(8) Install wheel and tire assemblies. Tighten stud nuts in proper sequence (Fig. 19), skipping every other nut until all 5 are torqued to 85 ft. lbs. (115 N�m). This is very important. Install wheel covers.
(9) Remove jack stands or lower hoist.
REMOVING CALIPER FROM VEHICLE
It will be necessary to remove the caliper to install a new piston seal and boot.
(1) Raise the vehicle on hoist or jackstands.
(2) Remove front wheel covers and wheel and tire assemblies.
(3) Disconnect flexible brake hose (Fig. 12) from tube at caliper. If piston is to be removed from caliper, leave brake hose connected to tube at frame mounting bracket. See �Disassembling Caliper�. Plug brake hose connector to prevent loss of fluid, or prop brake pedal to any position below first inch of travel.
(4) Remove retaining screw, retaining clip (and anti-rattle spring) that attach caliper to adapter (Fig. 5). Carefully slide caliper out and away from disc and adapter. Remove outboard shoe assembly from caliper, see �Brake Shoe Removal�.
(1) To remove piston, support caliper assembly on upper control arms on shop towels to
absorb any hydraulic fluid loss. Carefully depress brake pedal to hydraulically push piston out of bore (brake pedal will fall away when piston has passed bore opening) prop brake pedal to any position below the first inch of pedal travel to prevent loss of brake fluid. (If both front caliper pistons are to be removed, disconnect flexible brake line at frame bracket after removing first piston. Plug brake tube and repeat procedure to remove piston from opposite caliper.)
CAUTION: UNDER NO CONDITION SHOULD AIR PRESSURE BE USED TO REMOVE PISTON FROM BORE! PERSONAL INJURY COULD RESULT FROM SUCH PRACTICE.
(2) Disconnect flexible brake hose from the caliper.
(3) Mount caliper assembly in a vise equipped with protector jaws. Caution: Excessive vise pressure will cause bore distortion and binding of piston.
(4) Remove and discard dust boot (Fig. 13).
(5) Using a plastic trim stick, work piston seal out of its groove in piston bore (Fig. 14). Discard old seal. Do not use a screwdriver or other metal tool for this operation, because of possibility of scratching piston bore or burring edges of seal groove.
CLEANING AND INSPECTION
Clean all parts using alcohol or a suitable solvent and blow dry, using compressed air. Blow out all drilled passages and bores. (Whenever a caliper has been disassembled, a new boot and seal must be installed at reassembly). Inspect the piston bore for scoring or pitting. Bores that show light scratches or corrosion, can usually be cleared with crocus cloth. However, bores that have deep scratches or scoring should be honed (Fig. 15), using Tool C-4095, providing the diameter of the bore is not increased more than .001 inch (.025mm). If the bore does not clean up within this specification, a new caliper housing should be installed. Install a new piston if the old one is pitted, scored or severely worn or if the bore has been honed. When using Hone C-4095, coat the stones and bore with brake fluid. After honing the bore, carefully clean the seal and boot grooves with a stiff non-metallic rotary brush.
Use extreme care in cleaning the caliper after honing. Remove all dirt and grit by flushing the caliper with brake fluid; wipe dry with a clean, lintless cloth and then clean a second time in the same manner or until clean cloth shows no signs of discoloration.
(1) Clamp caliper in vise (with protector jaws).
Caution: Excessive vise pressure will cause bore distortion and binding of piston.
(2) Dip new piston seal in clean brake fluid and install in groove in bore. Seal should be positioned at one area in groove and gently worked around the groove, using fingers, until properly seated. Make sure that fingers are clean. NEVER USE AN OLD PISTON SEAL. (Be sure seal is not twisted or rolled) (Fig. 16).
(3) Coat new piston boot with clean brake fluid leaving a generous amount inside of boot.
(4) Position dust boot over piston.
(5) Install piston into bore pushing it past the piston seal until the piston bottoms in the bore (Fig. 17).
(6) Position the dust boot in the counterbore. Using a hammer and Tool C-4691 with C-4171 handle, drive the boot onto the counterbore (Fig. 18).
CAUTION: Force must be applied uniformly to avoid cocking.
Before installing caliper assembly on vehicle, inspect braking disc. Conditions are described in �Checking Braking Disc for Runout and Thickness� paragraph.
Examine the shoe assemblies for wear, damage, and fluid contamination. If they are in satisfactory condition, be sure that they are installed in their original position. If not usable, the shoe assemblies on both front brakes must be replaced.
(1) Slide outboard shoe assembly in recess of caliper.
CAUTION: No free play between brake shoe flanges and caliper fingers (Fig. 9) should exist (which might cause brake shoe rattle). If free play is evident by vertical shoe movement after installation, remove shoe from caliper and bend flanges (Fig. 10) to create slight interference fit to eliminate all vertical free play when shoe is installed. Install shoe after above modification, if necessary, by snapping shoe into place with fingers or with light �C� clamp, protect new lining from damage or contamination by using old shoe over new lining and across caliper fingers (Fig. 11).
(2) Position inboard shoe in position on adapter with shoe �flanges� in the adapter �ways� (Fig. 7).
(3) Slowly slide caliper assembly into position in adapter and over disc. Align caliper on machined ways of adapter.
(4) Install anti-rattle springs and retaining clips and torque retaining screws to 180 in. lbs. (20 N�m). The inboard shoe anti-rattle spring must always be installed on top of the retainer spring plate (Fig. 5).
(5) Attach brake hose to caliper using new copper washers on both sides of connector block.
(6) With bleeder screw open, allow caliper to �Gravity� fill with brake fluid, then close bleeder screw. (Be sure all air bubbles have escaped; replenish brake fluid in master cylinder reservoir. Bleed brakes as described under �Brake System Bleeding Procedures".
(7) Pump brake pedal several times until a firm pedal has been obtained.
(8) After bleeding caliper, check for fluid tightness under maximum pedal pressures. (Recheck master cylinder reservoir level).
(9) Install wheel and tire assembly. Tighten stud nuts in the proper sequence. (Fig. 19).
(Skip every other nut going around) until all 5 are torqued to 85 ft. lbs. (115 N�m). This is important. Install wheel cover.
(10) Remove jackstands or lower hoist.
(11) Road test vehicle and make several stops to wear off any foreign material on the brakes and to seat the linings. The vehicle may pull to one side or the other if this is not done.