Problem with axle shaft / rear wheel bearings 308

that is why I kneel in front of this man before each trip. I has worked so far
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Martin,

There is a percentage of americans that still think the earth is flat! I was just kidding actually and and am amazed at your cad cam drawings. I am thinking that the problem lies with the mondial hubs, however the gt4 had 3 totally different uprights and the rubber seal on mine did not fit and spun off. With the exception of a river crossing FCA trip I do not want to go into I never drive the car in the rain or water so hoping to keep rust out of there. I even had a post on it below read down it as it shos the parts diagram. I thought I had reassembled my hub wrong however I think I got a different shaft - hub assembly. I am curious as to which inner flange you have a think it is the later type with the seal?

http://ferrarichat.com/forum/showthread.php?t=42062&page=2&highlight=rubber+seal

It definitely seems like the weak point is your red line area. I am still amazed at the force the rubber bushings handle and the fact that only a few threads hold each wheel bolt to the hub!!!

Rob

 

I pulled 'em out this afternoon and the inspection guy is picking them up tomorrow. He's doing mag particle first and if that's okay will check for internal flaws with "shear wave".

A post by Ric Rainbolt in one of the other threads regarding a conversation with an ex FNA rep made the problem seem very real to me. I remember Ric from the old days on Flist in 1995 so I respect what he as to say . .. he's been around for a while and from his post he personally had that conversation with the Ferrari rep. If I didn't track my car it wouldn't concern me as much FWIW . . .but it's a Ferrari . .. thought that's what it was what it was built for (no don't go there . . count to 10 .. breathe ).



Sean

 

I think that the issue at hand is the fact that stub axles suffer scorching and scoring as the bearing's inner surface race rotates on the hardened/machined/polished shaft sections....leading to scorching/scoring/galling/discoloration and finally, metal transfer(getting nastier now...), and ultimately, a total fgailure-SNAP!
What are people trying to do here?
Analyze the failure sequence.
Or, analyze the repair process-the "proper" new part from Ferrari, the really expensive method.
Or, the mental masturbation of "re-inventing the wheel" for a car for which it makes totally no financial sense to do so...
and, since this happens to ALL V-8s(I have experienced this on 288 GTOs, F-40s, TestaRoasters, BBs, BBis, C/4s, Daytona Coupes, and Spyders and I think a 400i(real bad memory on these cars!)
I think we are all clear on this phenomena...yes?

I like the car magnafluxer, he can only crash, the pilot can drop from the sky-while true, this is technically a survivable mishap, which will tell well in the years to come.
Ahhh.
My turn: Military Sub-contractor. The art of US Nuclear Submarine component repairs....you plain can't have a mishap or you lose a "special" vessel.
These are, after all, the greatest engineering masterpeices man has created to date. Politics aside..let's be real here if we are going to discuss materials sciences and proper failure analysis.

I can repair these axles by a process used by-and certified by-the USN for these special vessels. Forget mag testing, and reading the x-rays...
My world goes: commercial, industrial, MILITARY, then SPACE....so we have FAA for those who insist, but NASA certification of materials is part of the repair job. Structual integrity, and most importantly, repair integrity, is certified.
Knurling the races' purchase suface, and then gluing it...fellas, there is a more elegant solution.
We will lightly camgrind the surface, check the axle with a variety of tests for integrity-these axles are NOT available. So we must have a good foundation-as I take the responsibility of the implied trust of the lives of the vehicles occupants...deadly seriously.


For reasons of simplicity, it is neccessary to "oversimplify" a rather complex and diffuse process.
Essentially I'm going to apply a plasma bath of similar metal to the axle. By manipulating components of the equation, a realtivley uniform coating of this plasma has been applied...where it counts most. It will have some surface discoloration issues-this is attributable to impurities in the axle, the plasma, and the atmosphere(inert gas cloud is great, but NOT perfect here).
I think of it as if I spray painted a vapour of matching welding mist to the shaft-never too thin, never too thick...the base metal "thinks that it has been welded", although the temperature was never even close....it is in the outer valence shell's bonding potentials in an artifically excited plasma environment...right?
Chemically clean, and bathed, re-camgrind to a specified dimension, re-analyze axles for bonding integrity, surface integrity, cracks, occlusions, sonictest, mag, x-ray, liquid penetrant, etc, etc, re-clean,re-finish, re-grind, re-finish, then the7 final integrity check list. Typically, I will camgrind to a specific bearing set with a specific interference as requested by customer.

This process will provide a surface which is suitable for a bearimg as used by Ferrari for this specific application.
What this metal transfer process cannot do, is provide a surface with the density and surface properties required to run a split shelled oil pressureized bearing with radiused side edges.
There are limits afterall....But, unequivocallyu, this fits, it works, it is safe, and getys around the dreaded-NO LONGER AVAILABLE. And, they will do this again...as there was insignificant tension due to it being too loose at point of manufacture to start with.
Cost per axle is a case by case basis-strictly-it is time consuming and must be worked in at the end of a project with any other NAVY contract jobs. The cost to tool up is not insignificant. There are, after all, less than a handful facilities who have been OK'd by the USN for this sort of work....
We are slow-so you are forewarned, but feel free to drop a line as you see fit,
carry on.

 

Dude.

Your car is far too clean...MINE is clean...yours is NASA clean room, white glove...... This is not healthy, Enzo would shake his finger.

PS: Come to the Santa Inez wine country tour, or better yet Willow Springs track days !! Lunch on me.

-L

 

FWIW my shafts checked out fine.

Pulling this apart again there are a lot of things a hack can do to this flange getting the outer bearing off or getting the shaft out of the upright . . like use the lug bolt threads for puller/pusher. Thought in one of the other threads the guy replaced three in the same car . .. this would be suspect for me.

I'll share this . .. in 1995 when I first bought this car I had new tires put on it . .. I personally saw the retard at Discount Tire put one of the lug bolts from the front in the rear and try and put a lot of torque on it . . the guy shook his head and acted pissed that the lug bolts were different . .. point being it indented the upright about .100 and would think probably stressed that part more than it sees on the road.

Knowing what my car has been thru and not seeing any flaws leads me to the conclusion that the ones that broke had been compromised some how. The quote from the FNA rep acknowledging the problem I'll take just like the PNA rep telling me the new P cars have a dry sump (they don't) . .. from my experience they are not as technical as they like to act . .. in fact I've coined the term "factory brained" instead of "factory trained" about these guys . .. again I'm just speculating and trying to put my world back in order.

FWIW seems like there's plenty used ones out there should someone discover a crack . . like to know when someone does.

Sean

 

Fatigue cracks when initiated by an alternating bending moment (like on said axle shaft) will always appear on the surface first, and over time will propergate into the fatigue characteristic famous "beach marks", erroding away section, untill ultimately not enough section remains to accept the load.
Magnetic Particle Inspection, (Magnaflux is a trade name of one of the supliers of MPI eqiupment) when used with the wet fluorecent fluid method with a strong magnetic high current field, will pick up these cracks even when quite small and more of a "crazing" nature than cracks. If this crazing appears, try and sand/polish it away untill it no longer appears under MPI inspection.
Stress concentrations are quite important in a fatigue sensative areas, and small radii give larger stress concentrations. As mentioned before in this thread, increasing the radii reduces the stress concentration and thus improves fatigue life.
Shot peening of particularly the radius will also improve fatigue life. This is because shot peening (when correctly aplied with round steel shot) will put a residual compressive stress into the metal's surface, and cracks do not initiate or propogate in a compressive stress enviroment.
Finally, and also mentioned before, proper torque into the assembly will reduce the alternating component of the load on the shaft, thus improving fatique life.

 

Hi Martin,

I am way not an engineer, only recently started wrenching on my 77, but have a long history of interest and reading Carroll Smiths stuff and am glad to hear your affirmation that shot peening is a significant way to extend part life.

I am particularly interested in trying to get a grip on how significant shot peening will help the life of THIS part. Having been in auto service, (as a service writer and occasionally manager), i have also done a lot of wrenching on auto x machines for 40 years and been very involved with their maintenance and improvement.

I know that it helps. How much, I ask you??? Clearly, it is a major pain to pull the stub, and probably doing a bearing replacement , while you are in there. I also know that it takes a lot of repetition to validate a process and render an opinion.

But just on your experience, or collected opinions of those you trust, how much will this help???

I have no feel for the beneficial effects of this process, and so I asked this question a lot earlier in the thread. I know it also depends on the strength of the original design and the metalurgy, (and consistency of the metalurgy), in the stock part, as well as the extent of the design overload.

If it were easy, we probably wouldn't be doing this

seriously concerned,
chris

 

For a dissertation on the benefits of shotpeening on fatigue life see;

http://www.metalimprovement.com/metal_fatigue.php

By exploring the website, you can also find MIC (Metal Improvement Company) locations near you.

Martin

 

Look at the difference between these two axle shafts.

If you look at the one that broke in the other thread it's slightly different also.

Unfortunately the replacement one on the right is probably an old itteration.

Just sharing.

Sean
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