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    Tech Common Drum Problems

    Uploaded by

    Gustavo Mosquera
    Scored drums have circumferential grooves on the braking surface and excessive lining wear. Drums can be rebored if scoring is within limits, otherwise replace immediately. Out-of-round drums vary in diameter and should be machined within limits or replaced. Excessive wear is usually caused by abrasive material and can gall the drum surface; replace drums scored beyond limits. Blue drums indicate excessive heat from an oversized diameter or weak springs; replace oversized drums or springs. Martensite spotted drums have hard raised spots and should be replaced unless detected early. Polished drums have a mirror finish and can be corrected by roughening or replacing linings.

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    Tech Common Drum Problems

    Uploaded by

    Gustavo Mosquera
    62 views3 pages
    Scored drums have circumferential grooves on the braking surface and excessive lining wear. Drums can be rebored if scoring is within limits, otherwise replace immediately. Out-of-round drums vary in diameter and should be machined within limits or replaced. Excessive wear is usually caused by abrasive material and can gall the drum surface; replace drums scored beyond limits. Blue drums indicate excessive heat from an oversized diameter or weak springs; replace oversized drums or springs. Martensite spotted drums have hard raised spots and should be replaced unless detected early. Polished drums have a mirror finish and can be corrected by roughening or replacing linings.

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    Scored drums have circumferential grooves on the braking surface and excessive lining wear. Drums can be rebored if scoring is within limits, otherwise replace immediately. Out-of-round drums vary in diameter and should be machined within limits or replaced. Excessive wear is usually caused by abrasive material and can gall the drum surface; replace drums scored beyond limits. Blue drums indicate excessive heat from an oversized diameter or weak springs; replace oversized drums or springs. Martensite spotted drums have hard raised spots and should be replaced unless detected early. Polished drums have a mirror finish and can be corrected by roughening or replacing linings.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    62 views3 pages

    Tech Common Drum Problems

    Uploaded by

    Gustavo Mosquera
    Scored drums have circumferential grooves on the braking surface and excessive lining wear. Drums can be rebored if scoring is within limits, otherwise replace immediately. Out-of-round drums vary in diameter and should be machined within limits or replaced. Excessive wear is usually caused by abrasive material and can gall the drum surface; replace drums scored beyond limits. Blue drums indicate excessive heat from an oversized diameter or weak springs; replace oversized drums or springs. Martensite spotted drums have hard raised spots and should be replaced unless detected early. Polished drums have a mirror finish and can be corrected by roughening or replacing linings.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    COMMON PROBLEMS WITH BRAKE DRUMS (Cont.

    Scored Drums
    Scored drums are signified by circumferential grooves on
    the braking surface and excessive lining wear. If the scoring
    is not deeper than the maximum rebore diameter, the drum
    may be rebored and returned to service. The linings should
    be replaced and the braking system should be checked to
    make sure excessive amounts of abrasive material are not
    entering into the lining-drum contact area. If the scoring is
    deeper than the maximum rebore diameter,
    replace the drum immediately.

    Out-Of-Round Drums
    Variations in drum diameter at different points on the braking
    surface indicate out-of-round drums. The drum should be
    machined within allowable rebore limits to restore concentricity.
    Do not exceed the maximum rebore limit of turned drums, and
    replace drums which are worn beyond their specified maximum
    diameter. If you are unable to restore concentricity by reboring
    the drum, replace it with a new one. It may be necessary to
    replace drums in pairs to assure proper brake drum balance
    and braking efficiency.

    Excessive Wear and Galling


    Excessive wear along the edges of the lining contact area, or in areas coinciding with the rivet holes of the lining,
    is usually caused by abrasive material collecting between the lining and the drum/rotor. Remove the abrasive
    material from the system and check the drum for scoring. If the brake drum is scored beyond the maximum limit,
    replace the drum immediately. Install dust shields to restrict the amount of abrasive material which can enter
    the braking system.

    Excessive wear can also be caused by misaligned brake shoes.


    If the shoes are not “square” to the braking surface, uneven
    forces are applied. This can result in deep grooves in the
    braking surface. If the brake drum is scored beyond the
    maximum limit, replace the drum immediately. Correct the
    brake shoe alignment to alleviate further grooving. Brake
    drum galling in an abnormal wear pattern is due to initial
    incompatibility between the brake drum lining and the brake
    surface. This condition may correct itself due to brake drum
    and lining wear. If severe, consider replacing the lining and/or
    the brake drum.

    9
    COMMON PROBLEMS WITH BRAKE DRUMS (Cont.)

    Blue Drums
    A bluish disfiguration on the brake parts (shoes,
    drums/rotors or bolts) indicates excessive heat.

    This is usually caused by an oversized brake surface


    diameter/undersized rotor width or by weak or broken
    return springs.

    For drums, check the braking surface diameter. If it is


    oversized, replace the drum immediately. If the return
    springs are weak or broken, replace them.

    Martensite Spotted Drums


    Martensite spotted drums have extremely hard, slightly raised, dark colored spots on the braking surface, shown
    uneven wear and the surface is out-of-round. This condition may cause excessive noise or shudder during brake
    applications. Unless this is detected very early, the brake drum should be scrapped.

    The spots are caused by very light brake applications with non-
    asbestos organic linings that are contacting the drum at a few
    lining high spots. To avoid this problem, change braking tech-
    nique to snubs rather than light dragging stops or ensure the
    lining fits the drum contour uniformly when it is new.

    Attempts to rebore a drum to remove the spots will usually ag-


    gravate an already bad situation, and if the drum is allowed to
    stay in service, cracks will connect between the martensite spots
    leading to brake drum failure. If the brake lining and drum are
    replaced and the same brake application techniques are used,
    the results will likely be the same. If only the drum is replaced, it
    may not develop these spots (as the high points are worn down).

    Polished Drums

    A polished brake drum/rotor is characterized by a mirror-like


    finish on its braking surface. Correct this problem by
    removing the gloss with 80 grit emery cloth. If the problem
    recurs, check the linings to make sure they are the proper
    friction rating. If the linings are glazed, consult the vehicle
    manufacturer for the proper lining material.

    10
    HOW TO MEASURE BRAKE DRUMS
    IDENTIFY REQUIRED DRUM BY MEASURING:
    Brake Surface Diameter Bolt Circle Diameter

    Brake Surface Width Size of Bolt Holes

    Overall Depth Pilot Diameter

    CHECK THIS INFORMATION:


    Number of bolt holes Drilled and tapped holes for skid control exciter
    Slots in the back of the drum for wheel spoke
    clearance

    11

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