d30 axle bearing interchangability question

I bought a hp d30 to replace the lp d30 in my '01. I think one of the axle bearings is shot in the hp since it has a bunch of slop in it so I was thinking I'd pull the ones from my lp. Looking online it appears that they have different part numbers and one references cast brakes. I'm not sure what the cast brake reference means, but I'm assuming that the bearings are not interchangeable between the two axles based on the different part numbers. Can anybody confirm that they are indeed different?

there is a change over year, I believe it was when they went from HP to LP. The unit bearings are like 1/4-1/2" deeper on the newer units IIRC. They are not interchangable due to the offset making the brakes not line up correctly etc.

XJ&TJ4ME said:

there is a change over year, I believe it was when they went from HP to LP. The unit bearings are like 1/4-1/2" deeper on the newer units IIRC. They are not interchangable due to the offset making the brakes not line up correctly etc.

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That matches the part number breaks that I am seeing.

I did some more searching and reading. Looks like the axles (inner and outer) are the same. Knuckles are the same. But if the axle bearing is different then are the brake calipers/rotors different? I'm trying to determine what all I can reuse and what I need to go ahead and buy for the axle swap.

Mid 1999 was the change over. 1990 to 2001 parts will interchange provided your hubs and rotors match, read on.

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 D30 axle. **

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 but should measure about the same.



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 ( see picture). These hubs use cast rotors.

On early 1990 - 1999 unit bearing/hubs the ring around 36MM shaft retaining nut is about 1/2 inch tall (see picture). These hubs use composite 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 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, 1990 to 1999.5 unit bearing/hub on the right

excellent information, thanks!