For the vacuum brake booster, the sprocket of the vacuum pump does not have sufficient strength, and therefore, its teeth may wear much more quickly than anticipated. If this problem is left unattended, the vacuum pump chain may come off and be stuck between the chain guides, and this could cause the rear cam sprocket to lock up, and in the worst case, the chain or the rear cam sprocket bolt could break. Either of these would cause the vacuum brake booster to stop functioning, and reduction of breaking efficiency would occur.