CRG Discussion Forum
Camaro Research Group Discussion => Restoration => Topic started by: Mike S on May 12, 2017, 01:11:10 PM
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Hello All,
Because my original 2-piece rotors were well below the min thickness rating that certainly would not pass NY safety inspection (even historic cars have to get at least a safety inspection in NY), I purchased a set of reproduction 2-piece rotors. You can get these at places like Jegs and get free shipping and save close to $60 vs. eBay. The mfg part number is BR69C.
For a reproduction these are very accurate especially in the hub shape areas. The only differences I see are the bolts that hold the hub to the rotor are metric 10.8 vs. the SAE grade 8, and the shape of the inner vanes. And of course the rim bolts are SAE threaded. The hub opening area where the rim center fits over is perfect and no slop. The thickness of the new rotors is 1" and the diameter is the same. I thought of swapping the hub between the two because of the type of iron(ductile) the original hubs are made from but decided to stay with the new ones even though they are gray iron. The rotor is gray iron which is the same as the original one and gray iron is pretty much what all modern rotors/hubs are made from today. The new rotors come with the inner bearing surfaces installed. The only thing I need to do is duplicate the green stripe on the hub.
Anyhow, I wanted to share my experience of these with you in case you are in a position whereby you have to buy replacements. I kept the originals in case one day just the rotors become available.
Mike
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Picture of rotor mounted
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That looks like a quality piece.
Thanks for the write up Mike. :)
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And the heads of the studs are different shaped.
The rotors look good! Thanks!
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The rotor only used to be available but no longer. Might've been a liability issue....Joe
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http://www.camarocentral.com/1967_1969_Brake_Rotor_Front_Disc_Rotor_Only_p/brc-634.htm
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wheel hubs are ductile iron today
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Just ordered 2 rotor only from Camaro Central, We'll see what happens. The last time I talked to them, they said rotor only was discontinued...Thank you, Joe
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Just ordered 2 rotor only from Camaro Central, We'll see what happens. The last time I talked to them, they said rotor only was discontinued...Thank you, Joe
Let us know if the order comes in. I called them a couple of months ago and they told me they were no longer available. I suggested to them at that time to update their web site.
Mike
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I kept the originals in case one day just the rotors become available.
Mike
I think you should just send them to me for safe keeping. We have no safety inspections where I live and I can run the rotors below minimum. Just kidding. Something else I need to look for. :'(
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In case they tell me no go, does anybody know the difference between the 139.00 rotors & their 225.00 rotors other than the price & one is off shore? I have several good hubs & wouldn't mind putting them back on the cars they came from....Joe
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I called Firebird Central (same company as Camaro Central )and they said those rotors are not available.
As for the difference in price between the $120 $225 2-piece (I assume you are looking at HBC), the hub is supposed to be ductile iron and the rotor is gray iron and made in the USA whereby the $120 unit is gray iron for hub, rotor and is imported. I wonder now if the reproductions, imported or not, still have to meet US requirements from DOT, NHTSA or whomever.
Mike
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Those prices actually came from Camaro Central....Joe
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The hubs have to meet MVSS (motor vehicle safety standards). I doubt if the re-pops have ever gone back through MVSS as cast iron material. We did a test at the proving grounds using Ford hubs made with cast iron that were designed for ductile back in the 80s - they failed under load at the road course.
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But what kind of cast iron? I've been reading up on it and see there are different types and see gray and ductile iron being commonly used today on items such as spindle hubs. I'm sure the usage depends in part on the type of vehicle used and expected usage.
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Automotive gray cast iron was either class 25 or class 30 depending on the application. That would be 25,000 or 30,000 psi ultimate tensile strength with very little deformation before breaking (brittle). Automotive ductile iron was typically 65-45-12. That is 65,000 psi ultimate tensile strength, 45,000 psi yield strength, and 12% minimum deformation before failure. The problem with using gray cast iron for wheel hubs is that it's weaker, but (more importantly) it fails traumatically without deformation (snaps). A ductile iron hub will bend when hit hard - allowing the driver to control the car after impact.
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It sounds like then that anyone who sells these rotors, including the main distributor, can be liable if indeed these hubs are not meeting MVSS specs and are the root cause for an accident. I assume then that parts manufacturers must provide some sort of proof of certification that they meet requirements?
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Sounds more & more like I'll need to buy the rotor assms & put the rotor itself on my hubs....Joe
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Well it's true. They are not available. I ask if they would be returning as they could be a high demand item. His answer was "I have no clue". Lovely. Back to the drawing board....Joe
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Well it's true. They are not available. I ask if they would be returning as they could be a high demand item. His answer was "I have no clue". Lovely. Back to the drawing board....Joe
Don't go too far - I've got a line on the rotors only, not terribly expensive, either. Let you know when I receive them and check them out - want to make sure these work before I release the source.
Regards,
Steve
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Awesome!
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Great Steve. Looking forward to your research results....Joe
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Gray iron is very brittle. If you drop it, I think it will crack. Ductile iron takes the gray iron and introduces other molecules, (primarily molybdenum I think) which acts to block cracks and stops them from continuing. Thus, you can make a crankshaft from ductile iron, but a gray iron one would crack immediately.
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Oh my Jimmy - that ductile iron explanation/comment is incorrect on so many levels!
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Bergy your going to have to explain why he is wrong, if your going to call him on it.
Level 1 ?
Level 2?
thanks
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Quick comparison between ductile iron and gray iron castings.
http://www.pentictonfoundry.com/news/differences-between-ductile-iron-and-gray-iron-castings-ductile-vs-gray-iron/ (http://www.pentictonfoundry.com/news/differences-between-ductile-iron-and-gray-iron-castings-ductile-vs-gray-iron/)
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OK - but the answer gets kinda far into the weeds! The foundry that I owned made 100% of the Motor Wheel hubs that they supplied to Ford & Chrysler passenger cars in the 80s. Also, I'm a metallurgical engineer - so here goes.
Ductile iron should be made from its own base iron. High production gray iron base has too many tramp elements in it which can hurt the elongation of as cast ductile iron. Also, gray iron melters often use scrap iron for melt stock that has too many tramp elements in it. Melt stock that contains thing like old bathtubs and steam radiators contains relatively high amounts of phosphorous. If used for ductile iron, phosphorus in the metal raises the brittle transition temperature too much. In which case - ductile iron becomes strain rate sensitive and can experience brittle failure at room temperature. Even at lower phosphorus levels - traumatic brittle impact can occur in severe cold weather environments.
The excellent elongation of ductile iron (versus gray cast iron) is achieved by adding magnesium as an alloy to the liquid iron post melt. The magnesium causes the graphite that precipitates out of the liquid iron as it goes through the solidification process to have a spheroidal morphology (round "nodular" graphite in the ferritic matrix). These spheroids of graphite don't interrupt the metal matrix of the iron as much as the "flake" graphite that is seen in gray iron. As a result - ductile iron can stretch before fracture a lot more than gray iron.
Gray typically has more pearlite stabilizers in the chemistry. So in addition to the graphite "flakes" interfering with its ability to "stretch", it also has a matrix that is just not conducive to ductility to begin with.
We didn't cast cranks, but to my knowledge - GM crankshafts from the late 60s were either cast or forged. Actually, one of the advantages of cast iron is that it has great anti vibration qualities. Also, after a million cycles (doesn't take long for a reciprocating part) it generally has an infinite fatigue life. Steel, on the other hand, will continue to propagate fatigue cracks to eventual failure even after a million cycles. I'm sure that many of you have noted these fatigue cracks when crack detecting old forged cranks. So, don't use forged cranks with significant cracks thinking that they aren't too bad. Steel fatigue cracks will continue to propagate to eventual failure. Cracks in cast cranks generally stop propagating when they hit the flake graphite structure (kinda like drilling a hole at the end of a crack to stop it from propagating).
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Bergy,
Can you tell the difference between gray and ductile iron by looking at them side by side?
Mike
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Great explanation Bergy. (you were the right guy to have on this thread!)
If I saw cracks on either cast, or steel that would be worrisome. But I understand the common thinking that the steel would continue to hold up, when actually the cast may last longer before failure.
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It's hard to tell the difference visually unless you know what to look for at the parting lines and in the size of the "in gates". Ductile iron requires larger feed gates and also needs larger risers to adequately supply iron to the solidifying casting. To tell if a casting is gray or ductile.... remember that those same flakes in cast iron that stop cracks from propagating also interfere with sound waves traveling through the matrix. So, if you tap a nodular casting with a hammer - it tends to ring like a bell. Gray iron just yields a dull thud. Sounds like a crude test, but we used the same principal to ultrasonic test 100% of the ductile hubs that we produced to make sure that they had acceptable nodular microstructure.
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When I get around to it I'll see about swapping the hubs that came with the rotors with the original ones. I'm sure (at least hoping) the bolt holes will line up.
Mike
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I'm glad you opened this discussion. It certainly has brought out some interesting point. I for one will be looking forward to your finds Mike. I need to get X66 714 back on all fours again but I'm not in so much of a hurry after reading some of the points here...Thank you, Joe
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Hi Joe,
I'll look at changing it this weekend. I'll closely compare the grain structures and even give it the "ping" check. I'll also weigh the two hubs to see if there is a difference.
Mike
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Talk about going to school, Bergy is the bus driver.
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Great read, Bergy! Thanks.
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I verified that the original hubs can be mounted on the reproduction rotors.
The original hub fit snug into the reproduction rotor (as well as the reproduction hub) so they are obviously machined the same.
I held both hubs (minus the rotors) by a lug nut and gave it the 'ping' test but they sounded exactly the same.
The hub/rotor bolt holes lined up exactly so I left the original hub mounted on the reproduction rotor and assembled the brakes.
Mike
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Thanks for checking that. I left an e-mail for my friend Hal Baer (Baer Brakes) to see if he would make a run of rotors only. I'm waiting for his response. If not I'll order the cheap rotor assm & use my hubs. Thank you, Joe
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If one is made out of cast and the other is ductile, those hubs shouldn't sound the same on the "ring" test Mike. Did the ring like a bell, or just have a dull thud?
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Good to know they fit! Did you re-use the original SAE, or the new metric bolts to mount the repro rotor on the original hub? Just wondered if the bolts are the same length.
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Hi Tim,
The bolts are the same length but the threads don't match so I reused the original SAE grade 8 bolts.
Mike
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If one is made out of cast and the other is ductile, those hubs shouldn't sound the same on the "ring" test Mike. Did the ring like a bell, or just have a dull thud?
I used a light weight hammer and tried on different parts and they had a dull thud. I could get a slight ring from the rotors though but I figured it was due to the circular shape that would allow some resonance.
Based on your experience with metals, if you had the rotor in your possession would you be able to tell what type of iron it is made from?
Mike
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we had the unmachined hubs traveling down a belt conveyor at the foundry. Hitting a ductile hub versus a cast iron hub yields a dramatic difference in "ring". We always cast a gray cast iron "test" hub & painted it fluorescent orange so that it wouldn't get mixed up with the ductile hubs. The test hub had to fail both the ring test and the ultrasonic test. it's the wheel hub that you should be ringing, nut the rotor itself.
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No 'rings' on the hubs and I've tried holding it by only one stud so as to minimize the possibility of absorbing any sounds.
Hmmmm.....maybe these hubs are not gray iron (aside from having a gray hue to it)?
Mike