Three different hub/bearing units were used over the years on XJ's. The hub/bearing units are the same part number for both sides of the vehicle. The model years for hub/bearing assemblies were:
1) 1984 through 1989 (early style rotors)
2) 1990 through mid-1999 (composite rotors)
3) late-1999 through 2001 (cast rotors).
** You need to match brake rotors to the unit bearing/hubs on your XJ. **
Lay the rotor on your bench and measure from the bench to the top of the rotor.
Composite rotors will have an overall height of 3 3/16". Composite rotors will have a thin sheet metal like appearance at the lug nut holes where the studs come through and measure about 1/8 "(.125) thick in this area. Composite rotors have a rounded off corner at the wheel mounting surface and look like two pieces joined together.
Cast rotors will have an overall height of 3 1/16". Cast rotors are thicker at the lug nut holes and measure between 1/4" (.250) to 5/16 (.320) in this area. Cast rotors have a square corner at the wheel mounting surface and look like they are one solid piece of metal.
Parts store replacement rotors may have a different appearance.
On late 1999 - 2001 unit bearing/hubs the ring around the 36MM shaft retaining nut is almost 3/4 inch tall and the hub has longer lug nut studs than older hubs.
On early 1990 - 1999 unit bearing/hubs the ring around 36MM shaft retaining nut is about 1/2 inch tall.
Two steering knuckle designs were used: 1984 to 1989 and 1990 to 2001. Left and right side knuckles have different part numbers.
Two types of brake caliper styles were used: 1984 to 1989 and 1990 to 2001. Left and right sides are different part numbers.
1999.5 to 2001 unit bearing/hub on the left uses a cast rotor, 1990 to 1999.5 unit bearing/hub on the right uses a composite rotor.
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