Any difference in hubs...?

[Bryson]

Is there any physical difference in Hubs between the cast and composite rotor'd XJ's? I'm trying to buy new hubs for my 99, but I'm not sure if there is a difference. I'm pretty sure I just have cast rotors, but I'm not exactly sure how to tell.

TIA
Bryson

[CJ7-Tim]

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.


Note the difference in the height of the ring around the 36MM axle nut and the different length of the lug nut studs.
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[balloo93]

Great info man, thanks.

[Bryson]

Can you also judge by the look of the rotor? From the pic it seems like the composite rotor has a rounded edge at the lugs, where as the cast has a typical 90deg angle.

There are two pictures of rotors, the top picture is a composite rotor and the bottom picture is a cast rotor.



VS

[EricsXJ]

Originally Posted by CJ7-Tim

Composites rotors will have an overall height of 3 3/16". Composite rotors will have a thin sheetmetal like appearance at the lug nut holes where the studs come through and measure .1/4 (.250) thick in this area.

Cast rotors will have an overall height of 3 1/16". Cast rotors are thicker at the lug nut holes and measure 5/16 (.320) in this area.

Very good post, but where did you get the measurements of the mounting flange? Those differ from the info I have. I ran into this when I installed the Warn manual hubs that require cast rotors and not composite. Per Warn, the cast rotors have a .250" mounting flange. I remember that when I measured my cast rotors (2000 XJ) they measured .250"... And per Warn, the mounting flange of composite rotors measure .125".

Also just to add to your descriptions of cast and composite rotors, the cast is one-piece and composite is two-piece. The difference can be seen in the photos above, making the top ones composite, bottom cast.

[CJ7-Tim]

Eric,
I was checking measurements on some spare parts and axles in my garage. They may be replacement parts which would explain the minor differences in the rotor thicknesses that I have vs the factory original rotors.

I have updated my original post and welcome any other corrections or additions.

[Mike94ZLT1]

How messed up is it that I have 1 of each?

[sprintagogo]

Originally Posted by Mike94ZLT1

How messed up is it that I have 1 of each?

Hey, do I win. I was right!

[Bryson]

Looking back on this thread reminds me. If I would have known what I do now I would have gone with the 84-89 style hubs for the roller bearings, and matched em with the rotors. Oh well.

[Mike94ZLT1]

Originally Posted by Bryson

Looking back on this thread reminds me. If I would have known what I do now I would have gone with the 84-89 style hubs for the roller bearings, and matched em with the rotors. Oh well.

Can I do that? Put 84-89 hubs and rotors on a 99?

[Bryson]

Originally Posted by Mike94ZLT1

Can I do that? Put 84-89 hubs and rotors on a 99?

I honestly havn't seen this done yet, but I've heard from a couple other members that it works without problem. The hub just a slightly different offset which is why it requires the matching rotor for the caliper to be in the right place.

[_Kyle_]

I remember me and smrtjustin sweating out his hub replacement (and u-joints) because he has aftermarket rotors and we really couldn't tell the difference. Lucky he ordered the right ones and we were all set. BTW, Rockauto has really great prices on Timken hubs - less than half the price of the dealer OEM ones.

[Mike94ZLT1]

Eh, nevermind... 84-89 hubs are more expensive, but the rotors are a little cheaper.

[jebmccall]

how much stronger are the roller bearing hubs, is it worth it to swap them out? i seem to go through hubs every 2 0r 3 months on my 99. thank god for the warranty

[wil badger]

Originally Posted by jebmccall

how much stronger are the roller bearing hubs, is it worth it to swap them out? i seem to go through hubs every 2 0r 3 months on my 99. thank god for the warranty

Stop buying junk unit bearings...Also what size tire and back spacing do you run ? It will make a huge difference in the life of the unit.