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  »  TECHNICAL INFORMATION
FAULTS IN BRAKE DISCS
WEAR
APPEARANCE
It is seen as wear on braking surface.
 
CAUSE
It occurs on normal operating conditions.
 
ACTIONS
Replace disc.
 
 
FINE HEAT CRACKS
APPEARANCE
It is seen as fine heat cracks.
 
CAUSE
It occurs on normal operating conditions due to normal heating and cooling of brake disc.
 
ACTIONS
If the cracks do not develop deeper than 1.5 mm, regring disc.

or replace the disc.
 
 
CRACKING
APPEARANCE
It is seen as deep surface cracks.
 
CAUSE
It happens due to excessive heating.
 
ACTIONS
Replace disc.

Check caliper operation.

Check balance between wheels, axle and trailer.
 
 
HARD SPOTS
APPEARANCE
It is seen as raised hard and colorful spots on braking surface.
 
CAUSE
It occurs on normal operating conditions due to normal heating and cooling of brake disc.
 
ACTIONS
It can be cleaned by turning if tolerance allows.

If it stays, replace the disc.
 
 
GROOVED DISC SURFACE
APPEARANCE
It is seen as grooves on disc mirror surface.
 
CAUSE
It is a kind of wear pattern.

It occurs because of that lining iron contact with the disc.
 
ACTIONS
If depth does not exceed 0.5 mm, regrined.

Replace disc.

Check linings.
 
 
BLUE COLOURING
APPEARANCE
It is seen as blue colouring on disc surface.
 
CAUSE
Excessive heating.

Hard braking.

Braking imbalance.
 
ACTIONS
Check braking system balance.

Check disc thickness.

Check caliper adjustment.
 
 
FRICTION IMBALANCE
APPEARANCE
It is seen as braking friction on disc surface.
 
CAUSE
Excessive heating.

Excessive braking.

Brake imbalance.
 
ACTIONS
Check caliper clearance and operation.

Check braking balance.
 
 
CORROSION
APPEARANCE
It is seen as rusting on ABS sensors.
 
CAUSE
Failure of anti-corrosive on ABS.
 
ACTIONS
Remove rust on the teeth with wire bush.

Re-coat with anti-corrosive paint.
 
FAULTS IN BRAKE DRUMS
 
GROOVED BRAKING SURFACE
APPEARANCE
It is seen as clear grooves on braking surface.
 
CAUSE
Brake shoe contacts with drum.

Excessively hard linings
 
ACTIONS
Replace linings and drum.
 
 
BROKEN MOUNTING CIRCLE
APPEARANCE
Brake drum seperated from mount circle.
 
CAUSE
Intense pressure of brake system.
Overloaded axle.
Poor mechanical resistance due to casting not being produced aaccording to international standards.

Excessive overheating and rapid cooling.
 
ACTIONS
Replace drum.
 
 
OVERHEATING
APPEARANCE
Blue/yellow discolouration seen as blueing effect.
 
CAUSE
Brake drum has been subjected to large accumulation of heating.

Incorrect shoe adjustment.

Excessively hard lining.

Brake shoe contacts with drum constantly.
 
ACTIONS
Replace linings and drums.

Ensure brakes are adjusted properly.
 
 
OVALITY
APPEARANCE
Imbalanced wear on braking surface.

Diameter A and B are different when measured at 90°

Driver can detect it on foot brake application by vibration or juddering.
 
CAUSE
Brake drum could have been dropped on a hard surface.

Hard impact on outer side of the drum.

Brake drum may not be holded properly in the course of turning process.
 
ACTIONS
Drum can be regrinded if tolerance allows.

If it is beyond the tolerances, replace the drum.
 
 
FINE HEAT CRACKS
APPEARANCE
It is seen as fine and short cracks on braking surface.

In early stages, the cracks may not affect the braking performance but should be inspected regularly.
 
CAUSE
Overheating of brake lining surface.
Constant heating and cooling of the drum

Using incorrect drum for application (For example; truck drum used on PSV application)
Incorrect lining use.
 
ACTIONS
Go for inspections to see if the cracks become more serious.

If it happens, replace the drum.
 
 
POLISHED DRUM
APPEARANCE
Mirror-like appearance on braking surface.

Reduction in braking performance.
 
CAUSE
Too hard brake linings.

Using the vehicle unloaded constantly.
 
ACTIONS
Sand brake surface of drum.

Use correct linings for application
 
 
CRACKED DRUM
APPEARANCE
Large cracks across braking surface.
 
CAUSE
Rapid and excessive heating and cooling (Thermal shock)

Brake drums not being casted or turned according to international standards.

Incorrect brake adjustment.
 
ACTIONS
Check brake systems for faults.

Check friction specification.

Replace the drum.
 
 
HARD SPOTS
APPEARANCE
It is seen as raised hard and colorful spots on braking surface.
 
CAUSE
It occurs on normal operating conditions due to normal heating and cooling of brake disc.
 
ACTIONS
It can be cleaned by turning if tolerance allows.

If it stays, replace the disc.
 
 
GREASED DRUM
APPEARANCE
Grease and oil stains on brake surface.

Driver can notice judder on foot brake application.
 
CAUSE
Defective hub oil seals.

Defective lubrication system.

Excessive use of grease.
 
ACTIONS
Clean all components.

Replace linings.

Replace hub/oil seals.

Check lubrication system.
 
 
STORAGE
APPEARANCE
Storing drums on their side may result in ovality problems.

Stacking drums inside one another could result in ovality and defects on the surface.
 
 
 
    •  GENERAL INFORMATION ON BRAKE DRUM AND BRAKE DISC
IN ORDER TO USE BRAKE DRUM AND BRAKE DISC FOR LONG PERIOD;
  • Do not overload your vehicle more than the load limit.
  • Try to drive your vehicle in the manner to use brake minimum.
  • While brake drum is being installed on hub, avoid using excessive force which may cause deformation on parts (e.g. using sledge hammer to install brake drum on hub or extract the brake drum from hub by hitting on it.)
  • Have periodic maintenances of brakes made.
  • The space between brake drum and brake lining (brake adjustment) should be controlled all the time. In addition, this situaiton increases fuel consuming.
  • Water contact with brake drum or brake disc should be avoided when they are hot. This will cause cracks on brake drums and brake discs.
  • You should not put the parking brake (handbrake)on when brake drums or brake discs are hot; you should wait them to cool instead; otherwise, ovality may form on the brake drum or brake disc surface.
 
WHEN SHOULD BRAKE DRUM BE REPLACED?
  • Brake drums of which diameter sizes are at the maximum level (finished brake drums).
  • Brake drums exposed to overheating.
  • Brake drums in which hard spots formed.
  • Cracked drums.
  • Brake drums of which wheel bolt holes become worn-out.
  • Brake drums of which lining surface have deep scratches which can not be fixed by turning.
  • Brake drums which are determined to be oval when controlled.
  • In order to have accurate effective braking performance, brake drums and discs should be replaced as pair.
 
    •  IMPORTANT RECOMMENDATIONS FROM FRENKA
  • . Before installing a new brake drum on hub, we strongly recommend that parts which contact with brake drum and hub should be cleaned if there are any faults such as rust, burr or scratch which may affect the balance. After this process, brake drum should be installed on hub. After installing process, balance should be adjusted by metal removing, when drum, rim and wheel is fixed. The reason is that they can never result in zero balance as brake drum and hub are separate parts from each other. It is the most accurate way to make finishing by metal removing when parts are fixed to each other. This does not mean that brake drum or hub is manufactured a result of balance defective production; however, they can not provide the balance of one part as they are manufactured separately from each other. We perform this process as if we combine brake drum and hub into one pice by turning. We strongly recommend to install brake drum in this way.

  • . More than half of the brake drum and brake disc faults are related to extreme heating. Brake drums and brake discs are heated parts because of the fact that they are made of cast-iron and they always contact with brake lining. There are some tasks to be done by drivers in this issue on extending life of brake drum and brake disc.
In order no to heat brake drum and brake disc;
  • Avoid excessive tonnage.
  • Try to decelerate as much as possible using retarder.
  • Use brakes at minimum level by using lower gears especially in sloping downward roads.
  • Do not try to cool the parts by using water, please wait them to cool by themselves.
  • Do not park your vehicle while emergency brake is on, especially when the parts are hot. This will result in ovality on brake drums and brake discs.
  • Sledge hammers and hammers should not be used when brake drums or brake discs are fitted on hub. They might be broken as the parts are made of cast iron.
 
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