Faulty brakes – faults and common defects
Checking the brakes
Here you will find useful basic information and handy tips relating to brakes.
Problems with the brakes, such as the widespread issue of brake judder, cannot always be traced back to faults in the brake itself. This page explains the causes that can lead to complaints regarding the brakes, and provides step-by-step instructions on how you can localize them.
Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.
TABLE OF CONTENTS
FAULTY BRAKES – FAULTS AND COMMON DEFECTS: Basic principles
Faults and common defects
Background information on problems and their causes in connection with disk brakes.
CHECK CAR BRAKES – MEASURES FOR IDENTIFYING SOURCES OF FAULTS: TROUBLESHOOTING
Check, determine and replace as needed: Tips on how to avoid complaints
Important notes and explanation
A basic prerequisite for every repair is that all components are cleaned, followed by lubrication of all necessary spots in the area of the guide shafts for the brake pads and/or at the mounting points of the brake shoes using a non-conductive, high-temperature-resistant, solid-free (non-metallic) paste from our product range that is suitable for ABS vehicles.
Do not use copper paste!
All components which were not assessed as OK must be strictly exchanged according to the guidelines of the vehicle, system, and brake manufacturers. Observance of the notes helps to avoid technical problems and complaints.
Follow the instruction leaflets!
Observe the instruction leaflet in the HELLA disk brake pad packages. Here you can find notes on special installation instructions, such as
- Directional disk brake pads
- Color marking of the backing plate and its meaning
- Warnings regarding work on the electro-hydraulic brake system
- Disk brake pads with removable foil on the rear plate for adhesive fixing, etc.
Take care when working on vehicles with an electro-hydraulic brake!
When working on vehicles with an electro-hydraulic brake (e.g. SBC Sensotronic Brake Control), never change the pads and the brake fluid at the same time! Work on the electronic brake system may be performed by trained personnel only.
Follow the instructions from the vehicle and brake system manufacturers!
Always follow the instructions from the vehicle and brake system manufacturers regarding repair and maintenance work.
CHECKING CONCENTRICITY AND NON-UNIFORM THICKNESS: INSTRUCTIONS
When carrying out the repair, test procedures such as checking the concentricity (lateral runout) and checking non-uniform thickness (varying disc thickness) of the brake disc may be required.
Checking the concentricity of the brake disc
- Perform the check with the discs installed ✓
- Fasten the brake disc to the wheel hub with all wheel nuts and corresponding washers ✓
- Fasten the dial gauge with holder to the suspension strut ✓
- Place the dial gauge approx. 10 - 15 mm below the outer radius of the disc and align with 'zero' ✓
- Turn the brake disc in the direction of travel ✓
- Measured over several wheel revolutions, deviations should not exceed 0.070 mm for new vehicles and 0.10 mm for older vehicles ✓
- The test only produces meaningful results for new brake discs. If deviations are found, the state of the wheel hub and bearing should be considered as additional fault sources ✓
Checking the concentricity of the wheel hub
- Attach the dial gauge and align it at the outer edge of the wheel hub ✓
- Turn the wheel hub at a constant speed in the direction of travel ✓
- Measured over several wheel revolutions, deviations should not exceed 0.03 mm ✓
- If the deviations are greater, replace the hub ✓
Note:
If hub eccentricity exists, the lateral runout at the outer edge of the disc will be twice as much.
Checking the friction ring for variation in thickness
The thickness difference measurement of a brake disc can only be verified using special measuring tools. A micrometer screw provides sufficient measuring accuracy of ± 0.001 mm.
The measurement should be taken at 12 to 15 positions on the circumference and approx. 10 – 15 mm below the outer friction radius. Depending on the vehicle type, judder phenomena can be caused by thickness differences as small as 0.012 mm to 0.015 mm. These values must therefore not be exceeded on new brake discs.
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