This is presented for your own conclusions.
By no means is it presented as the only cause or the only possible conclusion that could be drawn.
Analysis of the S197 Front Wheel Bearing Hub Assembly
This will be an exploration article on design of the S197 front wheel hub.
A good friend got me a failed hub and I proceeded to tear it apart and investigate the failure.
Here are the results of what I found.
First of all we are dealing with a pre-assembled hub that is not rebuildable in the conventional sense.
You canít just remove the seals and repack the bearings and replace the seals.
This assembly also does not contain the standard tapered roller and cup design bearings.
It is built with Ball Bearings. There are two sets an inner and outer set of Ball Bearings contained within a cage for each. There is an inner tapered race that supports the bearing balls, and an outer race that is machined into the hub casting.
This presents some rather unusual engineering decision questions.
Ball bearings are great for high speed and radial (Up and down) loading. But fair poorly for axial (Left and right) loading.
A question I present at this point is why use a Ball design when axial loading will clearly be applied during turns and normal driving situations?
A Tapered Roller design would be a far better choice for this application.
A Tapered roller design will carry a high load in both the axial and radial directions.
This is why it is the most common wheel bearing found within the industry.
However it also the most costly.
Below is a picture of the disassembled hub assembly.
Below is a picture of the Hub showing the machined surfaces, and races.
So now we continue to the failure analysis.
As we look into our housing to examine the outer race for causes of the failure we immediately notice a deformation of the race surface. The deformation appears as a wavy design in the race. This is a clear indication of axial load damage.
Below is a picture of the damaged outer race caused by axial loading of the bearing.
Below is a picture of the damaged inner race caused by axial loading of the bearing.
The failure of the hub assembly was caused by axial loading being applied to the Ball Bearing outer race surface.
The design of the wheel hub could be vastly improved by machining for the use of Tapered Roller bearing cups and races.
Additionally the cost of machining the hub assembly may be able to reduced thereby offsetting the increased cost of using the Tapered Bearing roller and cup design.
Advantage to the customer is preventative maintenance (Repack and Bearing and seal replacement) could be performed.
Advantage to the manufacturer would be easier machining thus reducing the cost to produce the hub.
Advantage to FMC would be less replacement under warranty.
Advantage to FMC would be reduction in catastrophic failure which could result in liability of FMC that could cause loss of life or damage to property.