WIS 33.00 Wheel Bearings Front Axle
Description - Wheel Bearings Front Axle
The next diagram shows the ABS slotted disc (also called a tone ring) and the hub seal.
Issues - Wheel Bearings Front Axle
- Bad bearings- need replacement
- Loose bearing nut, need adjustment
- Repacking of bearings
Part Numbers - Wheel Bearings Front Axle
These numbers are for a W220 2003 update S500L EU spec.
- Outer wheel bearing: 002 980 6502
- Inner wheel bearing: 140 981 0305
- Hub seal and ABS Wheel Speed Slotted Disc (ABS Tone Ring): 022 997 9747
WARNING - Use of Aftermarket Inner Wheel Bearings Front Axle
WARNING: Do not use aftermarket inner bearings without carefully checking that they perfectly match a genuine M-B bearing.
In particular notice the shape of the inner shoulder on the inner bearing on the side that is in contact with the axle back flange. Genuine M-B bearings have a small radiused shoulder. Some aftermarket bearings have a square shoulder. (The next diagram shows a complete but good M-B inner bearing compared with aq bad inner bearing. Only the race is shown as the bad bearing had to be destroyed by being ground with an angle grinder to produce a wafer thin section to allow it to be removed. See scorch mark where the split occurred.)
The radiused shoulder on the inner bearing fits neatly against the radiused edge on the axle flange. If an inner bearing with a square edge is used it will interfere with this radiused edge and the hub will not be in the correct position. The area of interference is shown in the next diagram.
The consequence of using an inner bearing with a square shoulder is that the wheel hub sits slightly proud by about 1mm to 2mm when installed on the axle. This also means that the clearance between the ABS tone ring and the ABS magnetic sensor is increased by the same amount and causes the speed reading sesnor to not work at all or not work properly. The magnetic sensor needs to be in very close proximity to the slotted ABS tone ring to generate adequate speed signals.
If the car is driven with this situation, after a few minutes, the instrument cluster will show ESP Failure and ABS Failure messages along with Drive to the nearest workshop being indicated.
If the gap is too wide, analysis with Star DAS will show that there is zero or an “implausible” speed signal generated by the front wheel ABS sensor.
The fix is to use genuine inner wheel bearings for the front wheels.
Replacement - Wheel Bearings Front Axle
- Raise car to full height.
- Chock rear wheels
- Loosen front wheel nuts.
- Jack up front of car and place on jack stands.
- Remove front wheel
- Remove brake calliper
- Support calliper to remove strain on abs wheel speed and brake wear sensor cables
- Remove Torx bolt securing brake disc to hub
- Remove brake disc.
- Remove dust cap. (For installation, fill the interior of the dust cap with high temperature wheel bearing grease. A smear of silicon will also help prevent any grease from leaking out and contaminating the wheel hub cap.)
- Undo Locking bolt on axle nut.
- Remove axle nut (For installation tighten nut and then back off to achieve 10 to 20 micrometres axial play in brake disc as measured by a magnetic base dial gauge clamped to the disc and measuring end of the axle.)
- Remove wheel hub. (If you are lucky the inner bearing and seal will come out with the hub.) (For installation ensure that there is no grease on the ABS tone ring and ensure that the hub is presented to the axle exactly square so that the inner bearing doesn’t cock on the axle shaft.)
- Clean off any remaining grease from axle.
- If necessary use and angle grinder to grind away part of the inner bearing until it is able to be split and removed from the axle.
- Do a final clean-up of the axle. (For installation, thoroughly coat the axle with high temperature wheel bearing grease before installing the hub.)
- Using a hammer and drift, knock off the ABS tone ring.
- Clean-up the wheel up of any old grease. (For installation, fill the interior of the wheel hub with high temperature wheel bearing grease.)
- Using a suitable diameter piece of bar stock, press out the outer bearing.
- Using a suitable diameter piece of bar stock, press out the inner bearing.
- Clean up the wheel hub.
- Pack the new bearings with high temperature wheel bearing grease. (An easy method is to place half a cup of grease in the corner of a plastic bag. Drop in a bearing and kneed thoroughly until the bearing is saturated with grease.)
- Install in the reverse order and repeat for the other front wheel.
