What is brake judder, brake pedal pulsation?
Brake judder or brake pedal pulsation is a vibration felt during braking. For example, your brakes may not vibration when stopping from speeds of less than 20-MPH but may vibrate when braking from 60-MPH. The vibration can vary from barely noticeable to a violent vibration felt in the brake pedal and/or steering wheel.
What causes brake judder or brake pedal pulsation?
The #1 cause of brake judder or brake pedal pulsation is disc (brake rotor) thickness variation (DTV) due to lateral runout. In other words, the brake rotor face is no longer perfectly parallel with the wheel hub and develops uneven wear or accumulation of friction material that varies its thickness.
DTV is a topic unto itself and since it causes the vast majority of brake noise problems you should learn more about what causes DTV and how to fix it. See this post on DTV.
Other things to check when you have brake judder and brake pedal pulsation or vibration
Check all of these possibilities before replacing any brake parts:
• Check for wheel bearing wear
• Check the rotor face for hot spots. Blue spots on the disc surface are a sign of rotor overheating. Hot spots change the friction characteristics of the rotor, causing the brake pad to slip/stick as it passes over the hot spots. Hot spots cannot be machined out. The rotor must be replaced.
• Check for overheated brake pads. Overheating from continued heavy braking can cause brake friction material to overheat and glaze. This causes slip/stick conditions.
• Check for proper caliper slide pin operation. Caliper slide pins must move freely in their bores. If caliper slide pins stick, the caliper and brake pads can’t apply and release evenly, causing pad glazing and disc thickness variation.
• Check for proper caliper piston movement and retraction. Corroded caliper pistons or worn or degraded square-cut O-rings prevent proper piston movement, resulting in pad glazing and disc thickness variation.
• Check for corrosion in abutment areas that can prevent proper brake pad backing plate movement.
• Check for pad imprints on the rotor. If you’ve performed heavy braking and left the overheating brakes applied for a long period, the pads can deposit a coating of the friction material on the face of the rotor. For a while afterward, the brakes will judder. Use 150 sandpaper in a circular motion to remove pad imprints.
• Remove the brake rotor and remove rust and corrosion on the hub surface.
• Machine the brake rotor to remove thickness variation or replace it with a new rotor.
• Use a dial indicator to check the lateral runout on the hub. If the hub is out of spec, rotate the rotor to clockwise to the next stud location and repeat the dial indicator. Repeat until you obtain the lowest lateral runout reading.
If you can’t correct lateral runout by rotating the rotor, use Brake Align™ – Runout Correction Plates or replace the hub.
Clean wheel mating surfaces. Remove corrosion and oxidation from wheels where they mate to the rotor hat to ensure proper torque
Install lug nuts with a torque wrench. Tightening lug nuts unevenly can introduce lateral runout. Always use a torque wrench set to the proper torque when installing wheels.
©, 2019 Rick MuscoplatPosted on by Rick Muscoplat