[SuperMacGuy]

I was at Summit Point yesterday for FATT. During my 2nd heat I had my left front hub fail. It let loose in turn 5-6 or so, and if you know Summit, that's about the slowest part of the track. Which is right after the part of the track with the highest pucker factor IMO (downhill at 80-100 depending, about a 30 degree turn a little off camber and max braking soon as you're through it). So I am OK and there is no body damage.
The hub flange sheared right off, and the wheel getting pushed back it must have bent up either the brake caliper or the slide pins, the caliper doesn't float any more. A guy with a TA next to me thankfully had a spare hub, so I got that on and drove carefully home. This was a Mike Minear hub so I'm contacting him to see if he wants to inspect it. I'll probably get a new one from him over the winter.
I'm thankful that was all relatively low drama. If that happened almost anywhere else on track, well all the other places are pretty high speed, and it would've been a real wreck, literally.

Chris

[StanIROCZ]

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.

[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.