Three different unit hub/bearing assemblies and disk brake rotor types were used over the years on XJ D30's. The unit hub/bearing are the same part number for both sides of the vehicle. The model years for hub/bearing assemblies were:
1) Orignial AMC hubs used 1984 through 1989 (
original type brake rotors and calipers, and orignal roller bearing hubs)
2) Older type unit hubs used 1990 through 1999.5 (
composite brake rotors)
3) New type unit hubs used 1999.5 through 2001 (
cast brake rotors).
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 designs were used: 1984 to 1989 and 1990 to 2001. Left and right sides are different part numbers.
** You need to match the disk brake rotor type and measurements to the unit bearing/hub type and measurements currently on your XJ. **
Previous owners or a repair shop may have installed different replacement parts. It is possible to have one old type and one new type unit hub.
Cast vs. Composite rotors Identification and Measurement -
Lay your old rotor on your bench and measure from the bench to the top of the rotor.
Be aware that your rotors may have been replaced previously and may have a different physical appearance than described and pictured below. The physical measurements will be the same as noted.
Composite rotors should have a rounded off corner at the wheel mounting surface and look like two pieces joined together. Composite rotors have a thin sheet metal like appearance at the holes where the lug nut studs come through and measure about 1/8 "(.125) thick in this area.
Composite rotors have an overall height of 3 3/16".
Cast rotors have a 90 degree angle edge at the wheel mounting surface and look like they are one solid piece of metal. Cast rotors are thicker at the lug nut stud holes and measure between 1/4" (.250) to 5/16 (.320) in this area.
Cast rotors have an overall height of 3 1/16".
*** Parts store replacement rotors may have a different physical appearance than the pictures, but should have similar measurements to the rotors currently on your D30 front axle. You must measure your current rotors and compare the measurements to the replacement rotors at the parts store before purchasing. ***
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If, after measuring your current rotors, you are still unsure of which type of rotor/bearing you have or if you suspect that a previous owner or a repair shop may have installed replacement parts, compare the Unit Hub Bearings to the pictures below.
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D30 unit/ bearing hubs, disk brake rotors, brake calipers, and axle shafts are interchangeable (1990-2001), and HP vs. LP. You just need to have the rotor type, match the hub type, cast vs. composite. Or, just swap the hubs and rotors as a matched set. The calipers are exactly the same, cast vs. composite or HP vs. LP.
2000 and 2001 XJ D30's are Low Pinion axles, just like the TJ Wranglers.
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Hub Type Identification -
- 1999.5 to 2001 unit bearing/hub on the
left of the picture uses the
cast rotor. The 1999.5 - 2001 unit bearing/hubs have the taller ring around the 36MM shaft retaining nut. It is almost 3/4 inch tall and the hub has longer lug nut studs than older hubs. See the axle shaft picture below.
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- 1990 to 1999.5 unit bearing/hub on the
right of the picture uses the
composite rotor. The 1990 - 1999.5 unit bearing/hubs have the ring around 36MM shaft retaining nut that is approximately 1/2 inch tall. See the axle shaft picture below.
