Dave's Place
Sliding Caliper Disc Brake

GENERAL INFORMATION

Two sliding caliper disc brake assemblies are used as follows:

1. Chrysler Single Piston Sliding Caliper Assembly:
   These units are positioned with a intermediate adaptor attached to the steering knuckle (Figs. 1 and 2).
   • RM300 (73-74)
   • M300 (74-78)
2. Kelsey Hayes Dual Piston Sliding Caliper Assembly:
   These units are positioned with a one piece adaptor attached to the steering knuckle (Figs. 3 and 4).
   • RM350 (73-74)
   • RM400 (73-74)
   • M300 (79 and Later)
   • M400 (74 and Later)
   • M500 (75 and Later)
   • M600 (76 and Later)

Brake operation and service procedures (except for number of pistons and component attachment) are essentially the same for either unit. Illustrations of the various service procedures will not always show any one brake. Both units consist of a two piece hub and disc assembly, the caliper, shoes and linings, splash shield and adaptor(s).

When the wheel is in motion the disc {ins (louvers) supplies air circulation for cooling. The braking disc is protected (inboard side) by the splash shield and by the wheel and tire assembly on the outboard side (Fig. 5).

Two machined abutments on the adaptor position and align the caliper. Retainers hold the caliper in the machined guides or "ways" on the adaptor and allow lateral movement of the caliper (Fig. 7).

Flanges on the outboard shoe (Fig. 3) are used to radially locate and position the shoe on the caliper fingers. All braking force for the outboard shoe is taken by the caliper. The inboard shoe is held in a captive position by the adaptor (Fig. 10) and this shoe reacts directly on the adaptor.

The caliper is a one piece casting with the inboard side containing the piston cylinder bore(s). A square cut rubber piston seal is located in a machined groove in the cylinder bore(s) to provide the hydraulic seal between piston(s) and cylinder walls.

A moulded rubber dust boot installed in a groove in the cylinder bore and piston keeps contamination from the cylinder wall and piston. The boot has a wiping lip that prevents contamination in the bore area (Fig. 6).

As the brake pedal is depressed, hydraulic pressure is applied against the piston(s). This force pushes the inboard brake shoe and lining against the inboard braking surface of the disc. As force increases against the disc from the inner lining, the caliper assembly moves inboard, sliding on the machined adaptor "ways" (Fig. 7), thus providing a clamping force.

When the brake pressure is released, the piston seal (distorted by applied pressure) returns to its normal position, pulling the piston back to released position (Fig. 6), creating a slight running clearance between outer shoe and the disc.

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, thus maintaining correct adjustment at all times.

METERING VALVES

All sliding caliper disc brakes are equipped with combination brake warning/metering valve (See "Hydraulic System Control Valves"). The metering unit of the combination valve is to better match the front disc brakes with the rear drum brakes on the vehicle. This results in improved braking and steering control.
Note:
1978 and later Dodge Motorhome Service Manuals refer to the combination brake warning/metering valve as a combination brake warning/hold off valve.

SERVICE CHECKS

1. The master cylinder fluid level should be checked at each lubrication period. Maintain fluid level to within 1/4 inch of the top of the reservoir. Use only clean brake fluid conforming to DOT 3.
2. Linings should maintain light contact with the disc or have no more than .005 inch clearance. How ever, 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 front 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. Lining wear should be checked at least every 12,000 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, a thrumming sound (front end vibration) or a pumping (up-and-down movement) of the brake pedal when braking a moving vehicle. Disc thickness must be checked 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. lf 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 efiiciency. Disc lateral runout should be checked whenever major service procedures are required on a sliding caliper disc brake system.

SERVICE DIAGNOSIS

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. 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 "Disassembly" paragraph). Check the mating surfaces of the abutments on the caliper and adaptor. If corroded or rusty, clean surfaces with wire brush. Inspect braking surfaces of disc.

Reassembly

1. Slowly and carefully push piston(s) back into bore until bottomed. Watch for possible reservoir overflow.
2. Slide new outboard shoe and lining assembly in recess of caliper.
   
   CAUTION:
   No free play between brake shoe flanges and caliper fingers (Fig. 12) 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. 13) to create slight interference fit to eliminate all vertical free play when shoe is installed.
   
   Install shoe after above moditication, if necessary, by snapping shoe into place with fingers or with light "C" clamp, protect new lining from damage or contamination by using old pads over new lining and across caliper fingers (Fig. 14).
3. Position inboard shoe in position on adaptor with shoe "flanges" in the adapter "ways" (Fig. 10).
4. Slowly slide caliper assembly into position in adaptor and over disc. Align caliper on machined ways of adaptor.
   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 spring and retainer assemblies and torque retaining screws to 235 inch-pounds.
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 and lining removal and installation. However, if a firm pedal cannot be obtained bleed the brake system as described in "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.
9. Remove jack stands or lower hoist.

Disassembly

1. Leave flexible brake lines attached to remove caliper piston(s), as follows:
   1. Single piston unit: support caliper assembly on axle and steering linkage 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 pedal to any position below the first inch of pedal travel to prevent loss of brake lluid. (If both front caliper pistons are to be removed, disconnect llexible brake line at frame bracket after removing first piston. Plug brake tube to remove piston from opposite side).
   2. Two piston units: support caliper assembly on axle and steering linkage. Place 2x4xl0 inch wood block spacer (Fig. 15) between caliper fingers and pistons (wood spacer must be FULL TWO INCHES thick, this is allowable dimension piston can be pushed out of bore and maintain hydraulic seal). Carefully depress brake pedal until both pistons contact wood spacer. Pistons can now be removed. (Disconnect flexible brake line at frame bracket and plug line to remove pistons from opposite caliper). Prop brake pedal to any position below one inch of pedal travel to prevent loss of hydraulic fluid.
      CAUTION:
      Under no condition should air pressure be used to remove piston(s) from bore(s) personal iniury could result from such practice.
2. Disconnect flexible brake hose from 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 Dust boot (Fig. 16).
5. Using a small, pointed wooden or plastic stick, work piston seal out of groove in piston bore (Fig. 17). 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 bore. (Whenever a caliper has been disassembled, a new boot and seal must be installed at reassembly). Inspect the piston bore for scoring or pitting. Install a new piston if it is pitted, scored or the plating is severely worn. 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. 18), using Tool C-4095, providing the diameter of the bore is not increased more than .002 inch. If the bore does not clean up within this specincation, a new caliper housing should be installed. Black stains on the piston are caused by the piston seal and will do no harm.

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 stiff non-metallic rotary brush.

Use extreme care in cleaning the caliper after honing. Remove all dirt and grit by tlushing 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.

Assembly

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 lubricant (supplied with kit) Ucon LB1145Y24 (or equivalent) and install in groove in bore. Seal should be positioned at one area in groove and gently worked around the groove, using clean fingers, until properly seated.
   NEVER USE AN OLD PISTON SEAL. (Be sure seal is not twisted or rolled (Fig. 19).
3. Coat new piston boot with lubricant (as specified above) leaving a generous amount of lubricant inside of boot. Install in caliper by working into outer groove, using fingers only. (Boot will seem larger than diameter of groove, but will snap into place when properly positioned in groove (Fig. 20). Using a forefinger, slide around inside of boot to be sure it is seated, or correctly installed.
4. Plug high pressure inlet to caliper and bleeder screw hole, (and opposite piston bore hole on two piston units) then coat piston with a generous amount of lubricant (as specified above). With fingers spreading boot, work piston into boot and press down on piston. (The entrapped air below the piston will force the boot around the piston and into its groove as the piston is depressed). Remove plug(s) then carefully push the piston down the bore until bottomed.
   Caution:
   Force must be applied uniformly to avoid cocking. Reinstall high pressure inlet and remove piston bore plug on two piston units and install second piston as described above. Before installing caliper assembly on vehicle, inspect braking disc. Conditions described in "Checking Braking Disc for Runout and Thickness" paragraph.

Installation

Examine lining for wear, damage or fluid contamination if its condition is found satisfactory it may be reused. If not usable both front brakes must be relined with new lining. If old lining is to be reused, be sure linings are installed in their original position.

1. Slide new outboard shoe and lining assembly in recess of caliper.
   CAUTION:
   No free play between brake shoe flanges and caliper fingers (Fig. 12) 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. 13) to create slight interference fit to eliminate all vertical free play when shoe is installed. Install shoe after above modiiication, if necessary, by snapping shoe into place with fingers or with light "C" clamp, protect new lining from damage or contamination by using old pads over new lining and across caliper fingers (Fig. 14).
2. Position inboard shoe in position on adaptor with shoe "flanges" in the adapter "ways" (Fig. 10).
3. Slowly slide caliper assembly into position in adaptor and over disc. Align caliper on machined ways of adaptor.
   BE CAREFUL NOT TO PULL THE DUST BOOT(S) FROM ITS GROOVE AS THE PISTON(S) AND BOOT(S) SLIDE OVER THE INBOARD SHOE.
4. Install anti-rattle spring and retainer assemblies and torque retaining screws to 235 inch-pounds.
5. Attach flexible brake hose assembly to caliper using new copper gasket(s). Tighten to 25 footpounds.
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. Bleed brakes as described under "Bleeding Disc Brakes" paragraph).
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 as described in "Front Axle" Group 2.
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.

1. Mount dial indicator C-3339 on steering arm with plunger contacting disc approximately one (1) inch from edge of disc (Fig. 22).
2. With wheel bearings adjusted to zero end play, check lateral runout. (Both sides of disc). Runout should not exceed .004 inch. If runout is in excess of specification, install a new disc and hub assembly or reface disc, being careful to remove as little as possible from each side of disc. Remove equal amounts from each side of disc. Do not reduce thickness below minimum thickness shown in refinishing section below. Be sure and readjust wheel bearings after check.
3. Thickness variation of disc should be made in conjunction with runout. Measure thickness of disc at twelve (12) equal points with a micrometer at a radius approximately one (1) inch from edge of disc. If thickness measurements vary by more than .0005 or .0008 inch, (see chart below) disc should be removed and resurfaced or a new disc and hub assembly installed (Fig. 22).
4. Light scoring and/or wear is acceptable if heavy scoring or warping is evident, the disc must be refinished or replaced (See Refinishing ( Refacing) Braking Disc). If cracks are evident the hub and disc assembly must be replaced.

Remove Disc and Hub Assembly

1. Raise vehicle on hoist or jackstands. Remove wheel cover and wheel and tire assembly.
2. Remove caliper assembly, as described under "Removing Caliper" paragraph, (but do not disconnect brake line). Suspend caliper from wire hook or loop to avoid strain on flexible hose.
3. Remove grease cap, cotter pin, nut lock, nut, thrust washer and outer wheel bearing.
4. Pull disc and hub off wheel spindle.

Inspection

Before refinishing or refacing a breaking disc, the disc should be checked and inspected for the following conditions:

1. Scoring, rust, impregnation of lining material and worn ridges.
2. Runout or wobble.
3. Thickness variation (Parallelism).
4. Dishing or distortion (Flatness).

If vehicle has not been driven for a period of time, the discs will rust in the area not covered by the lining and cause noise and chatter, excessive wear and scoring of the discs and lining. Wear ridges on the discs can cause temporary improper lining contact if ridges are not removed before installation of new lining (pads).

Lining deposits on the disc, may cause erratic friction characteristics if new lining is installed without resurfacing or cleaning the disc.

Excessive runout or wobble in a disc can increase pedal travel due to piston knockback due to necessity of caliper to follow the disc wobble.

Thickness variation in a disc can also result in pedal pulsation, chatter and surge due to variation in brake output when disc section is uneven.

Dishing or distortion can be caused by extreme heat and abuse of the brakes.

Resurfacing Braking Disc

This operation can be used when the disc surface is rusty or has lining deposits. A sanding disc attachment will remove surface contamination without removing much material. It will generally follow variations in thickness which are in the disc.

Install Disc and Hub Assembly

1. Slide brake disc and hub assembly on spindle.
2. Install outer bearing, thrust washer and nut.
3. Tighten wheel bearing adjusting nut to 240-300 inch-pounds while rotating disc and hub. Recheck disc runout as described previously.
4. Back off adjusting nut to release all preload, then retighten adjusting nut finger tight.
5. Position lock nut on nut with one pair of slots in line with cotter pin hole. Install cotter pin.
6. Clean grease cap, coating inside with wheel grease (do not fill cap) and install cap. Clean both sides of braking disc with alcohol or suitable solvent.
7. Install caliper assembly, as described in "Installing Caliper" paragraph.