Article No. 87-20-15

BRAKE - FRONT DISC - SHUDDER DURING LIGHT BRAKE APPLICATION - SERVICE TIPS

SHUDDER - FRONT DISC BRAKE - DURING LIGHT BRAKE APPLICATION - SERVICE TIPS

MERKUR: 1985-87 XR4Ti

ISSUE: Front disc brake shudder during light brake application from highway speeds may be caused by a front wheel and tire assembly, brake rotor, or front hub assembly.

ACTION: If service is required, it is important that the shudder is properly diagnosed. Use the exact sequence of the following service procedure.

1. Road Test

a. Road test to check for front brake shudder.

b. Front brake shudder is most noticeable when braking at highway speeds of 55-65 mph (88-104 km/h). Drive vehicle up to highway speed.

c. Lightly apply brake and note speed when shudder occurs. Front brake shudder is felt as a vehicle shake and steering wheel nibble.

d. Return to critical speed and apply hand brake only. If vibration is noticeable when hand brake is applied, this indicates rear brake shudder. If vibration is only noticeable when foot brake is applied, a front brake shudder is indicated.

2. Inflation Pressure Check

Check tire inflation pressure and condition of tires. All tires should be set at 28 psi.

Figure 46:

3. Wheel and Tire Assembly Runout Check

a. Jack front of vehicle off ground. Place support underneath control arm to prevent suspension movement.

b. Using a radial runout gauge (Rotunda Tool 007-00014 or equivalent) measure radial and lateral runout, Figure 46.

c. Mark low and high positions. Radial runout must not exceed 1.6 mm (0.063 inch). Lateral runout must not exceed 1.8 mm (0.071 inch).

4. Wheel Runout Check

a. Using a dial indicator, measure wheel rim lateral runout on inner machined rim. Record high and low positions. The wheel rim lateral runout must not exceed 0.5 mm (0.0197 inch).

b. Measure wheel radial runout at wheel rim along machined inside edge of rim. Radial runout must not exceed 0.4 mm (0.016 inch).

NOTE: If reading for wheel runout is within specification and tire runout is outside specification, tire must be rotated on wheel rim until tire runout is within specification. Recheck tire radial runout until an OK specification is obtained.

Figure 47:

5. Brake Rotor Thickness Variation Check

a. Remove front wheel and tire assemblies.

b. Examine condition of rotor and pad assemblies.

c. If there is evidence of lining deposits or light corrosion on rotor, this should be removed using emery paper and a flat block.

d. Check thickness variation of rotor using a suitable micrometer, Figure 47. Measure rotor at eight (8) positions 45~ apart about 15 mm (1/2 inch) in from outside diameter.

NOTE: It is important to always check at a constant radius.

e. If any readings vary by 0.01 mm (0.0004 inch) or more, rotor should be replaced using E7RY-1125-C along with new brake pads (E6RY-2001-A). Before installing new parts, it is important to perform check in Step 6 and install rotors as described in Step 7.

Figure 48:

6. Hub Face Runout Check

a. Remove rotor, clean hub face, and check hub face runout just inside wheel studs, Figure 48. This figure must be within 0.06 mm (0.002 inch) total indicator reading.

b. If hub is outside specification, a new hub must be installed. Refer to the Merkur XR4Ti Shop Manual, Section 11-16.

Figure 49:

7. Rotor Installation and Runout Check

a. Using appropriate nuts (temporary) install new rotors. Seat rotors onto hub face.

b. Using a suitable dial indicator and holding fixture, measure rotor runout, Figure 49. Measure runout about 10 mm (7/16 inch) in from outside diameter.

c. Rotate hub and rotor assembly. Record indicator reading. If runout is greater than 0.08 mm (0.003 inch) total indicator reading, rotor should be repositioned on hub at 90~ increments until a reading of less than 0.08 mm (0.003 inch) is obtained.

d. Once a reading of less than 0.08 mm (0.003 inch) is obtained, the position of rotor on the hub must be marked to make sure of reassembly in this same position.

e. Remove temporary nuts and install wheel and tire assemblies.

8. Balance Check

Check tire and wheel balance using an on-car balancer.

PART NUMBER PART NAME CLASS

E7RY-1125-C Brake Rotor C
E5RY-1104-B Hub Assembly - L.H. C
E5RY-1104-C Hub Assembly - R.H. C

OTHER APPLICABLE ARTICLES: Supersedes 86-10-4
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION: SP872015A - Diagnose and replace both rotors and pads
TIME: 1.4 Hrs.

OPERATION: SP872015B - Diagnose and replace both rotors, pads, and one hub
TIME: 1.8 Hrs.

OPERATION: SP872015C - Diagnose and replace both rotors, pads, and both hubs
TIME: 2.2 Hrs. DLR. CODING: Basic Part No. 1125 - Code: 67