Checking the brakes

Checking the brakes

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Brake problems such as the widespread brake rubbing are not always due to brake faults. On this page, we show which causes can lead to brake complaints and how to track them down step by step.

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.

Check car brakes – measures for identifying sources of faults

Check, determine and replace as needed: Tips on how to avoid complaints

Checking brakes - measures to identify sources of faults - Wheel bearings

Wheel bearing

Play/damage

Wheel hub

Clean (metallically bright)
Axial run-out deviation using dial gauge
Detectible damage
Corrosion protection (no solid constituents)

Axle nut

Strength and securing

Wheel bolt thread

Damage
It must be easy to manually screw in the bolts

Transverse control arm bearing

Replace in the case of increased play or porosity

Checking brakes - measures to determine sources of error - Control arms

Transverse control arm

Replace in the case of increased play or porosity

Caution! Depending on the axle design, an impermissible play can be difficult to determine..

Checking the brakes - measures to identify sources of error - suspension joint Fig. 1

Checking the brakes - measures to identify sources of error - suspension joint Fig. 2

Supporting joint

Tie-rod end

Joint play
Check sealing collar for porosity and leaks
Fixing of joints (locking screws)

Checking the brakes - measures to identify sources of faults - Brake calliper Fig. 1

Checking the brakes - measures to identify sources of faults - Brake calliper Fig. 2

Brake caliper

Piston

Leak-tight, smooth running, dust sleeve
Leak-tight, porous

Caliper housing

Damage

Slide piece

Play, smooth running
Seal

Checking brakes - measures to identify sources of faults - Brake hose

Brake hose

Leak-tight, porous, chafing points
Inner diameter (swollen)
Screw connection
Observe maximum service life

Checking brakes - measures to identify sources of faults - Suspension strut

Suspension strut

Leak-tight (detectable oil leakage)
Damper performance test in advance
Broken spring
Damper mounting
Mounting

Caution!
Chassis changes impact the effect and comfort of the brake system.

Checking the brakes - measures to identify sources of faults - Drive shaft boot

Drive shaft sleeve

Leak-tight, porous

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 brake systems 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

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

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.

Please always observe the model-specific technical specifications of the vehicle manufacturer in this regard.

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