Front Wheel Bearing Hub Failure Analysis

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

and Failure

Ok here we go.

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 can’t 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.

Conclusion:

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.

Rich Sr.

Because it's designed to fail. They're suppose to be changed at 100K miles. It also cuts down on HAZMAT of grease, rags and cleaning solvents involved in the older style bearings. It also makes it so having the right tools and skills to do it right is required, IE, take it to the dealership,=job security and they can keep track of your car and download the on board puter. The backyard, shadetree mechanic is slowly being completely elimanated from the scene. Fed regs.

This failed at around 20k.
They are cheap to buy so (Less than 100 bucks) so the cost isn't as great a concern.
Something to watch for though.
Some of the mystery clunking in the front end could be something to look at.

Rich Sr.

Rich Senior,

I must say that I've seen an exceeding number of these bearings fail during my time as a mechanic, and I must also say that there has always been one commonality between all the failures I've noticed...

95% of the failed front wheel roller bearings of this configuration have been AFTER there has been front axle work, like swapping CV joints or rebuilding the tranny etc..

They fail in my experience mostly because the axle nut did not have the proper amount of torque applied to it after assembly...

I don't know how that factors into your estimations on the subject, it also don't seem like the issue you experienced above, but it's a factor nonetheless that I thought you should hear about.


FE

Originally Posted by FEandGoingBroke

Rich Senior,

I must say that I've seen an exceeding number of these bearings fail during my time as a mechanic, and I must also say that there has always been one commonality between all the failures I've noticed...

95% of the failed front wheel roller bearings of this configuration have been AFTER there has been front axle work, like swapping CV joints or rebuilding the tranny etc..

They fail in my experience mostly because the axle nut did not have the proper amount of torque applied to it after assembly...

I don't know how that factors into your estimations on the subject, it also don't seem like the issue you experienced above, but it's a factor nonetheless that I thought you should hear about.


FE

That is good info to have.
This hub was on a car from the factory so the factory could have installed incorrectly. No way of knowing.
Also I have heard of others that were Factory installed also but failed between 20 and 30k.
Luckily all started grinding in a turn as opposed to a catastrophic failure.
Ford sells a bunch of them so I dont see it as going away.
I was thinking of getting a pair and having a machine shop cut them out so I could install Tapered roller bearings and cups and have it rebuild-able.
Plenty of meat in the casting to do it.
Call it a Mod if ya like but I think it would be a good approach.
But I haven't taken the time to really dig into that.
Shouldn't be a big deal to do though.
Winter project eh?

BTW this is the same design on many Ford sedans and coupes.

Thanks for the info and feedback.

Rich Sr.

no prob. and thank YOU for the write up! It's a good one.

After working at a Ford Dealership in the trenches and at parts stores, Dodge Ram Trucks have the biggest failure rate and cost the most. Many people don't understand that curbs, potholes and 4x4 abuse is a major failure cause.

That's a no brainer with me and JustJim

Being confused looks good on you.

Keep it up

Welcome to FM!


FE

The point of the article was to show how the old Fox style hubs were superior in strength than the newer SN95/S197 hubs. Basically, if Ford wanted to spend the couple of dimes per hub, they could have combined the best features of the Fox and SN95 hubs to make a better hub. But alas, the bean counters won.