DISC MOUNTING - BOLTED


Most racing and many high performance road brake discs are designed to be mounted on to the hub or stub axle by means of a mounting bell. Mounting bells are usually made from high grade Aluminium Alloy, although other materials can be used.
This arrangement is much lighter than a one piece disc and bell, but more importantly allows some compliance to reduce the risk of distortion due to heat expansion of the disc. This becomes more important the larger the disc and is considered essential above Ø330mm diameter. 


For lower duty applications and on smaller discs a bolted mounting is sometimes preferred for strength and simplicity especially for off-road application (e.g. Rallies) where debris may clog a floating mechanism leading to run-out and disc vibration. However, stiff flat bells should be avoided with a bolted mounting. 
Standard AP Racing disc mounting hole size is 6.40 / 6.45mm diameter. AP Racing offer a range of bolts, nuts and washers to suit this configiration, intended to be assembled as illustraded.

Available in reuired quantity (per disc):

E8 - 6 Lobe Headed Brake Disc Boliting Kit

Also, available in boxes of 100:

E8 - 6 Lobe Headed bolt - Box of 100
1/4" UNF Nut - Box of 100
1/4" Washer - Box of 100
**Note: Disc mounting tightening torque - 14Nm (10.5lb/ft)

DISC HANDING & IDENTIFICATION

Most AP Racing Brake Discs feature Curved Vanes. The brake discs are handed and should be installed with the cooling vanes running back, from the inside to outside diameters in the direction of rotation as indicated in the sketch below.
DISC BEDDING FOR COMPETITION USE

All cast iron brake discs for competition use need to be bedded-in to ensure heat stabilisation and improve resistance to cracking. Cracks or even disc failure can occur during the first few heavy stops if careful bedding is not carried out.AP Racing recommend the following procedure:

If ducts are fitted they should be ¾ blanked off.
Use previously bedded pads.
For a minimum of 15 Km use brakes gently at first from initially low speeds - progressively raise speed to normal racing speed but still using gentle applications.
For the final 2 or 3 applications brakes can be used quite heavily.

If AP Racing thermal paints are used then only the Green paint (430°C) should have fully turned to white and maybe also just the Orange paint (560°C) on the outside edges of the discs during the bedding procedure.

SAFETY & CARE OF DISCS
Cast iron brake discs should not normally be operated at bulk temperatures in excess of 610°C and above rotational speeds of 3000 revolutions per minute.
Discs must be regularly and frequently inspected for excessive heat crazing and cracking.
Discs with cracks emanating from mounting holes / slots, inside diameter, scallops, or outside diameter should be changed immediately.
After heavy and prolonged use some surface crazing will often be evident. If this turns into distinct surface cracks which are radiating towards the inside or outside diameter the disc should be changed.
IF IN DOUBT REPLACE