Jeep Unit Bearings

[jagular7]

Jeep's unit bearings are not created equal. I have taken apart many coiled front front axles for the various parts that swapped between them. Or at least I presumed.
After a trail ride to Clayton, my passenger unit bearing decided to show its wearing signs. I swapped it out once I got home with one I had on the shelf.
Well, the one on the shelf is ~1/4" too short in distance between the mounting surfaces of the bearing. The eccentric center also has a raised lip on it.
When swapping it on, mounting to the knuckle was no problem. The axle stub was no problem. Mounting the rotor no problem. Didn't realize the rotor was held against the raised lip on the center flange with a 1/4" gap. Put wheel spacer on no problem. Assembled caliper on the knuckle, aligned with rotor, no problem. Mounted wheel, no problem. Everything appeared to be tight.
Drove here/there (1-2 times), no problem. Then driving for 45 min, the front tire started to wobble. I figured my spacer nuts were getting loose as the wheel lugs were tight. Once I took everything apart, found a unit bearing stud pulled out and all the nuts loose on the spacer. Typical I anticipated as I didn't use locktite on the spacer lugs. Reassemble and got everything tight. Couldn't get the caliper on and to align with the rotor. Couldn't rotate the rotor as it was up against the knuckle.
Took a while, but finally figured out the mounting surface difference was putting the rotor against the knuckle. Swapped in another used one and I'm all better.

Pics. To add, the lugs on the wrong unit bearing are longer as well.




What had happened, I didn't get the rotor on correctly, so the spacer wasn't installed correctly. With the push/pull of the wheel while rotating/turning, it put torque-arm pressure on the spacer nuts. In time, they rotated loose and the rotor moved over the flange lip, giving more movement and torque-arm pressure. I did mess the rotor up some with the center and lug holes, but its reusable.

The measurement for the correct unit bearing mounting surface distance between the wheel and knuckle is 2-1/8". The shorter unit bearing is 1-7/8".

[ovrszd]

Yep, been there. For years I thought all D30 front axles were created equal. After gathering several different donor vehicles and beginning to swap parts we found the same problem you've found.

The difference is unnoticeable at a glance. Only by laying the hub assembly on the floor and noticing the different deck heights will you realize they are not alike.

Dangerous situation that requires careful scrutiny to avoid what happened to you. Luckily for you the whole thing didn't fly apart while driving down the road.

That I know of there's not even a technical guide to go by. For example a certain year and application not crossing with a different certain year and application. The differences seem to be random. :(

[spunebil]

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[rrock]

Have this in my bookmarks from awhile back, take it for what it is worth.

There are pictures at the link, just copy/pasted the text.

http://jeepforum.com/forum/f11/any-d...e-hubs-360959/


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) Original AMC hubs used 1984 through 1989 (AMC brake rotors and calipers, and roller bearing hubs)

2) Older type unit hubs ( Jeep Part number 53007449 ) used 1990 through 1999.5 (Composite brake rotors).

3) New type unit hubs ( Jeep Part number 5016458 ) used 1999.5 through 2001 (Cast brake rotors). .

Two types of steering knuckle designs were used: 1984 to 1989 and 1990 to 2001. Left and right side steering knuckles have different part numbers.

Two types of brake caliper designs were used: 1984 to 1989 and 1990 to 2001. Left and right sides calipers have 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.

If your hubs and rotors are not compatible, there will be interference between the two parts, the tire/wheel assembly will be bound up and not move freely, and the Jeep will not move.

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. ***


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.

.......................

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.

[spunebil]

1098876543431

[jagular7]

Measure the mounting surfaces of the unit bearing and the wheel surface.



This picture shows quite a bit of detail difference.
1 - longer studs on the short unit bearing.
2 - taller front center hub with a ridge line in the middle
3 - bearing outer housing fits tight against the lug plate
4 - lug plate does not have a raised center hub on the back side

But without completely knowingly what to look for.....

[spunebil]

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