Hub failure at Summit Point, thank God it was at low speed Options

[00 SS]

The part was "supposed" to be a forging. Either the individual part that failed was a very bad forging or a casting passed off as a forging. My supplier, mark Williams Enterprises, believed them to be forgings. They buy generic blank axle shafts from another supplier, they do not forge their own parts. So they are at the mercy of their supply as well.

A cast part with the exact right amount and type of heat treatment might work, but I think in this case the part is better off starting with the stronger forging.

Carburizing is an interesting idea, but I don't know if the blanks can be obtained in 8620 or not. It's my understanding that 4340 is not particularly well suited to carburizing. Yes, no? 4340 is what the blanks are supposed to be made of. But it is something I can discuss with Mark Williams.

Originally, through hardening was selected because it is the easiest process to control and the only process Mark Williams offered me. I know they now have induction capabilities, but I don't know if they had it when we first started making this part. It's worth revisiting with them as is carburizing. If we can get the heat treating profile right with either of these process, it would likely result in a stronger and more durable part.

I think the first hurdle is making sure the blanks are properly forged in the first place.

I really appreciate all the help and knowlege I'm getting from all of you. It's invaluable. Please keep it coming.

Thanks,

This post has been edited by 00 SS: Jan 17 2011, 06:03 PM

[StanIROCZ]

Carburizing is an interesting idea, but I don't know if the blanks can be obtained in 8620 or not. It's my understanding that 4340 is not particularly well suited to carburizing. Yes, no?

Yes, my understanding is that 4340 already has too much carbon for carburizing since carburizing adds carbon to the surfaces. It might be good for induction?

I really appreciate all the help and knowlege I'm getting from all of you.

It is a noble cause so I’m glad to help.


Question on a different subject, what happened to the ‘Hardbar’ or whatever hubs that were made for the corvettes and why wouldn’t the C4 version work on the 4th Gen?

[00 SS]

They only made C5 hubs. They never completed their C4 version to my knowlege. Also, I think the factory C6 Z06 hubs are basically the same as the Hardbar C5 hubs, so I think they stopped making them as well since you can put the C6 Z06 hubs on any C5/C6. I think SKF actually sells the C6 Z06 hubs as HD C5/C6 hubs.

[StanIROCZ]

Does the tone ring have the same tooth count? Would an easier solution be a new upright to accept the C6 hubs?

[00 SS]

A new upright with a C6 Z06 hub would be a good solution, but only for those that are allowed to change those parts within the rules of the sanctioning body they run with.

[PeteL]

The main issue I had with the material of the failed parts is that they were a relatively porous casting.

I thought they were made from an axle shaft forging?

You can make castings work, in fact the Duralast hub that I also examined was a casting but a much better one.

I'm really surprised to hear you say that a casting is acceptable for this part. If for no other reason one surface on the factory spindle has a bearing surface, and bearing life is very dependent cleanliness of the steel, and castings are very unclean. Brake rotor type 'old school' hubs are castings but are much more beefy i.e. not a ~1.25” dia shaft. Nothing about the Duralast part would surprise me however.

Most bearing components are heat treated to HRC 60. Pete, could you do a hardness check on the factory hub? Sean sent me one a couple years ago; the part I looked at was a forging and appeared to be induction heat treated. I’m betting it is HRC 60.

The same is true for carburizing, nitriding and induction hardening. I wouldn't feel comfortable with any of these processes without some level of destructive evaluation to make sure they were done correctly.

Not saying that it’s not a good idea but I know it is common not to cut carburized parts on low volume stuff. I’m no expert so don’t quote me on this, but my experience has been that it really depends on the source and how much experience they have with the material/ size/type/spec of the part and how comfortable they feel about it. On the other hand induction hardening is a total PIA for low volume and needs many cuts to get right. This hub is a safety critical part so care needs to be taken.

One of the factors that Mike will have to weigh is how well he believes he can monitor the quality and consistency of any given process he uses Large automotive companies have specialists to do just that. Some processes are easier to do that with than others.

True statement.

I plan to take a core and case hardness on the Duralast part but it will have to wait until our hardness tester gets fixed. I was surprised it was a casting too but it appears to be a good one. But a forging is always going to be better than a casting.

My experience with carburized camshafts is that a few parts will be cut up initially to qualify the source. I can't remember if there was any batch testing. Certainly in the aerospace industry we require cutups of test coupons for each batch of parts carburized in addition to the initial qualification.

One thing to keep in mind with carburizing is that you usually have to finish grind areas of tight dimensional tolerance after carburizing because there is usually some distortion from the quench. Then you have to check for grinder burn. Nitriding eliminates the need for finish grind but is more expensive and you have to decide if you can live with the surface iron nitride "white" layer or remove it. I'm not sure if Mike's hubs have any areas that require that tight a tolerance but it's something to check before committing to carburizing.

Honestly, I think a through hardened forging will be a big improvement over the casting and will be much easier for Mike to ensure it's done right. A simple hardness test could be done on each part as a process check.

[PeteL]

Does the tone ring have the same tooth count? Would an easier solution be a new upright to accept the C6 hubs?

I believe Unbalanced is working on this very thing, in addition to new a-arms.

[SuperMacGuy]

Would an easier solution be a new upright to accept the C6 hubs?

Excuse my ignorance, but are the C6 hubs:
A. Better because they are designed more robustly
B. Better because they are "in production" parts and we can get good GM units still
C. Better because they are easier to reproduce
D. Better because someone else is already making replacements units that are proven
??

[00 SS]

Primarily A. They are a stronger factory design using larger bearings than before. But they still use ball bearings and are sealed units. SKF sells them for around $500 each I think.

[CMC #37]

I know someone who went the Corvette hub route on their f-bod. They are happy so far!

[00 SS]

Any details of how they implemented it and which corvette hubs they are using? C4 hubs are an easy bolt on, C5/C6/C6Z06 would be a major project.

This post has been edited by 00 SS: Jan 18 2011, 06:16 PM

[CMC #37]

Any details of how they implemented it and which corvette hubs they are using? C4 hubs are an easy bolt on, C5/C6/C6Z06 would be a major project.

I think they went with C4 hubs, I'll get back.

[Chevy053]

Does anyone know how long the C6-Z06 or 'Hardbar' hubs last for Vette owners? is it significantly longer than how long our hubs last?

[Mojave]

Does anyone know how long the C6-Z06 or 'Hardbar' hubs last for Vette owners? is it significantly longer than how long our hubs last?

Be careful when dealing with Gary from Hardbar. He burned me bad once (missed a track weekend that I paid for because he didn't ship a part and then lied about it).