Brake pedal vibration

1. When applying brakes, a pulsating force tries to push the brake pad back occurs. The pulsation is transmitted to the brake pedal.
2. The following are the main possible causes of brake judder:

Due to an excessive runout (side-to-side wobble) of disc plate, the thickness of disc plate is uneven. 

1. If the runout is more than 0.05 mm {0.002 in} at the position 10 mm {0.39 in}  from the disc plate edge, an uneven wear occurs on the disc plate because the pad contacts the plate unevenly.
2. If the runout is less than 0.05 mm {0.002 in}  , uneven wear does not occur.

The disc plate is deformed by heat. 

1. Repeated panic braking may raise the temperature in some portions of disc plate by approximately 1,000 °C {1,832 °F}  . This results in deformed disc plate.

Due to corrosion, the thickness and friction coefficient of disc plate change. 

1. If a vehicle is parked under damp conditions for a long time, corrosion occurs on the friction surface of disc plate.
2. The thickness of corrosion is uneven and sometimes appears like a wave pattern, which changes the friction coefficient and causes a reaction force.

Inspection and repair procedure 

Fig 1: Inspection And Repair Procedure Flow Chart

Courtesy of MAZDA MOTORS CORP.

Lateral runout inspection 

1. To secure the disc plate and the hub, tighten the hub nuts upside down or insert a washer (thickness 10 mm {0.39 in}  , inner diameter more than 12 mm {0,47 in}  ) between the hub bolt and the hub nut.
   NOTE:

   • The component parts of the SST (49 B017 001 or 49 G019 003) can be used as a suitable washer.
2. After tightening all the hub nuts to the same torque, put the dial gauge on the friction surface of disc plate 10 mm {0.39 in}  from the disc plate edge.
3. Rotate the disc plate one time and measure the runout.

   Runout limit 

   1. 0.05 mm {0.002 in} 

   Thickness variation inspection 

   1. Clean the disc plate-to-pad friction surface using a brake cleaner.
   2. Measure the points indicated in Fig 2 using a caliper (micrometer).
      Fig 2: Identifying Measuring Points

      Courtesy of MAZDA MOTORS CORP.
   3. Subtract the minimum value from the maximum, and if the result is not within specification, machine the disc plate using a lathe.

      Thickness variation limit 

      1. 0.015 mm {0.00059 in} 
      WARNING:

      • Do not exceed minimum disc plate thickness.