I need to replace the front rotors on my ‘66 as they are below the minimum thickness requirement. Who are the preferred vendors I should contact to obtain new rotors? thanks
Replace Front Rotors on a ‘66
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Once-upon-a-time, when front rotors were available from GM, they were available only as an assembly with hub. Quite frankly, that is the best way to replace the rotors. However, the GM assembly, GM #3867311 was discontinued in December, 1971 and replaced by GM #3998278 which was discontinued in July, 1999. I know of no brake/hub assembly for your application that is currently available. So, you'll have to purchase rotors without hubs, remove your hubs from the existing rotors, and install. I think any major brand rotor will be fine. However, if it matters to you, you're going to find that virtually all rotors available today, regardless of brand, are going to be of off-shore manufacture.In Appreciation of John Hinckley👍 1- Top
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John, Are your rotors riveted to the hubs? If so, they're original. You'd have to remove them and drill out the rivets.
I suggest Bair's rotor and hub assembly in Mark's link. I'd think they could take your hubs as a partial exchange, or possibly use your hubs with new USA rotors, riveted and lathe turned.
If you just change rotors, your hubs may have excessive runout which will cause problems.
You would have to get them turned on a lathe as an assembly at a local brake shop, re-rivet or bolt together or simply place chiseled witness marks for future reference if removed.
An alternative method would be to just get new rotors and using a dial indicator, check for runout and use thin shim stock between hub and rotor. Personally, I won't use this method, but others have done this successfully.
Rich👍 1- Top
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If you just change rotors, your hubs may have excessive runout which will cause problems.
You would have to get them turned on a lathe as an assembly at a local brake shop, re-rivet or bolt together or simply place chiseled witness marks for future reference if removed.
Rich
Bring the assembly without bearings installed to a local shop, and have them turned so they are true. You can hold the rotor in place using backwards lug nuts, or some have tapped the rivet holes and used a countersunk head Allen screw to retain the rotors.
You can't just install the rotors and go driving, else your braking system will have problems with runout and air pumping.Vice-Chairman (West), Michigan Chapter NCRS
71 "deer modified" coupe
72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
2008 coupe
Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.- Top
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This is what I would do if you decide to replace them yourself.
Bring the assembly without bearings installed to a local shop, and have them turned so they are true. You can hold the rotor in place using backwards lug nuts, or some have tapped the rivet holes and used a countersunk head Allen screw to retain the rotors.
You can't just install the rotors and go driving, else your braking system will have problems with runout and air pumping.
What you suggest will work providing that the rotor-hub assembly does not result in excessive runout on the rotor. In that case, the machining process on the rotors can result in their being below the thickness limit. At the very least, some of the rotor's "wearability" is consumed in the process. It would not be this way ifUNFINISHED SERVICE rotors were available. As far as I know, they are not. When the rotor/hub assembles were originally manufactured, UNFINISHED rotors were installed and riveted to the hubs and then the rotors were machined. In this manner, the finished rotor was true to the hub centerline and the rotor thickness was set at the new rotor dimension.
One thing that can be done now, though is this: assemble the new rotor and and existing hub as you described above. Measure the rotor runout. Then, correct the runout using the TAPERED SHIMS available from Raybestos. If the rotor can be brought into acceptable runout specs with a shim(s), you're done. If not, a final machining can be done but with the use of the shims to correct most of the runout, the machining will remove a lot less of the rotor thickness than if shim(s) were not used.
In Appreciation of John Hinckley- Top
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John,
You can buy rotors from vendors and ship them to you. You will be paying more for an imported rotor and shipping. I use NAPA premium rotors, I am setting up a set now in fact. Available virtually everywhere in the country.
I would deburr both the hub and new rotors. Bolt them on and check the runout. I never cut rotors, front or rear.
I have been tapping and bolting them on using flat heads in place of the rivets for decades. Dialing the runout under 003". I have literally done this 100's of times and never had a problem or comeback.
However, tapping and bolting them on is not necessary, most don't do it. But you should torque all 5 nuts on the rotor when checking the runout and once you get them dialed-in, loosen and recheck. If the runout doesn't change, you're done.- Top
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Gary, What approximate percentage of all of your past front rotor assemblies required the Raybestos shims? Am I safe to assume it's been near 100%.
The available sizes I see are 0.003", 0.006", and 0.009", cost is around $17 each. This would add about $35 for a front set.
Plus labor and materials to drill and tap 10 hub locations for attachment, and 10 rotor holes drilled to size the bolts and clearanced/beveled to accept the flat head Allen bolts. Then assembly labor, then final runout checks.
On all of my past C2 restorations, for front brakes, I chose the assemble method with reversed lugs, rotate rotor for minimal runout, recheck, and lathe turned as an assembly. I typically ended up with 0.002" or less runout. I would then chisel mark the hub/rotor for future match reference.
My final rotor thickness always ended well above minimal spec after lathe turning the assemblies.
I feel either method, yours or mine, yields the same results.
The only drawback I see with shims is that you'd need to stock a large quantity of various sizes.
Do you also use the shims for trailing arm rotors?
Joe, et al....
A final thought... I could never understand why GM did not machine front hubs for zero runout. The hubs had to be face machined on lathes, so why their machine was not more accurate is a mystery to me.
Was it Corvette only, or all GM front disc hubs? If so, that was millions of hubs.
Maybe it was simply cost effective for GM, with the benefit of future guaranteed revenue for more costly Service assemblies versus selling just the rotors.
Rich
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Gary, What approximate percentage of all of your past front rotor assemblies required the Raybestos shims? Am I safe to assume it's been near 100%.
The available sizes I see are 0.003", 0.006", and 0.009", cost is around $17 each. This would add about $35 for a front set.
Plus labor and materials to drill and tap 10 hub locations for attachment, and 10 rotor holes drilled to size the bolts and clearanced/beveled to accept the flat head Allen bolts. Then assembly labor, then final runout checks.
On all of my past C2 restorations, for front brakes, I chose the assemble method with reversed lugs, rotate rotor for minimal runout, recheck, and lathe turned as an assembly. I typically ended up with 0.002" or less runout. I would then chisel mark the hub/rotor for future match reference.
My final rotor thickness always ended well above minimal spec after lathe turning the assemblies.
I feel either method, yours or mine, yields the same results.
The only drawback I see with shims is that you'd need to stock a large quantity of various sizes.
Do you also use the shims for trailing arm rotors?
With either front or rear rotors, I always prep both the axle/hub surfaces and the mating rotor surface first. Then when I get to dialing in the round out, I first bolt them up and check them. I work with both new and used rotors/axles, and usually the original front hubs.
Almost all the time I am going to bolt the rotors on, so that prep work is done long before dialing in the rotors.
Once I know what the runout is I go back and recheck the mating surfaces for any minor burr I might have missed.
While I can chuck a hub or axle in my lathe, I don't like taking a chip on those in most cases.
Years ago, I wanted to test the results of finish turning a bolted-on rotor. I had to use my buddy's lathe since the swing on my South Bend wasn't enough. I bolted on the rotor to GM rear rotor and kiss cut it. Checked runout and it was -0- using a Starrett 001" indicator. Then I unbolted the rotor and retorqued in, on the lathe. Rechecked it and the runout was 0015-002". Still very good but not worth the time to machine the parts unless they will never be disassembled. With fronts, that probably is the case, with the rear you may sometimes need to get to the parking brakes.
I shim when needed for both front and rear. There has been some thought that shimming won't work, or will distort the rotor, or the sky will fall. I can say, if done correctly- that is the key, they work fine. I don't use the NAPA shims you refer to , and I don't know if they're still available. I simply use my toolmakers shim punch kit and common ss shims from 001-012" in 001" increments.
As mentioned, when all is said and done, the runout I use is under 003". Works so well a fellow in FL copied it and claims it as his own work. Rotor runout I can fix, someone's integrity I can't. As for what % of front and rear rotors I shimmed, hard to say. I do record a lot of information about each build I do, but what shims were used for rotors is not one of the spec's I keep. I have had rotors bolt on with under 003" runout without any shimming required, but by far they all are over 005", some up to 008".- Top
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Mark, I spoke to Bairs and they no longer sell the Used Front Hub with New Rotor assembly listed in their catalog and they no longer sell USA made rotors. Did you ship your rotor hub assembly to Bairs for rebuild whereby they riveted and turned your existing hub to a new rotor? And, would most local brake shops do this type of work? Thanks to all for your very informative replies,- Top
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Mark, I spoke to Bairs and they no longer sell the Used Front Hub with New Rotor assembly listed in their catalog and they no longer sell USA made rotors. Did you ship your rotor hub assembly to Bairs for rebuild whereby they riveted and turned your existing hub to a new rotor? And, would most local brake shops do this type of work? Thanks to all for your very informative replies,
My apologies to you...I should have mentioned I had lots of the drivetrain; brake parts; and a differential to rebuild/rework when I drove them up there and delivered them back in 2004.
They had enough meat left on my rotors that they could just turn them down to spec (as I recall) and most definitely did excellent quality work...
I'm sorry mine was so long ago...but I still think they are a quality vendor for our C2s.
Sorry that USA made stuff is no longer handled by them.
thx,
Mark- Top
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Hi Rich,
With either front or rear rotors, I always prep both the axle/hub surfaces and the mating rotor surface first. Then when I get to dialing in the round out, I first bolt them up and check them. I work with both new and used rotors/axles, and usually the original front hubs.
Almost all the time I am going to bolt the rotors on, so that prep work is done long before dialing in the rotors.
Once I know what the runout is I go back and recheck the mating surfaces for any minor burr I might have missed.
While I can chuck a hub or axle in my lathe, I don't like taking a chip on those in most cases.
Years ago, I wanted to test the results of finish turning a bolted-on rotor. I had to use my buddy's lathe since the swing on my South Bend wasn't enough. I bolted on the rotor to GM rear rotor and kiss cut it. Checked runout and it was -0- using a Starrett 001" indicator. Then I unbolted the rotor and retorqued in, on the lathe. Rechecked it and the runout was 0015-002". Still very good but not worth the time to machine the parts unless they will never be disassembled. With fronts, that probably is the case, with the rear you may sometimes need to get to the parking brakes.
I shim when needed for both front and rear. There has been some thought that shimming won't work, or will distort the rotor, or the sky will fall. I can say, if done correctly- that is the key, they work fine. I don't use the NAPA shims you refer to , and I don't know if they're still available. I simply use my toolmakers shim punch kit and common ss shims from 001-012" in 001" increments.
As mentioned, when all is said and done, the runout I use is under 003". Works so well a fellow in FL copied it and claims it as his own work. Rotor runout I can fix, someone's integrity I can't. As for what % of front and rear rotors I shimmed, hard to say. I do record a lot of information about each build I do, but what shims were used for rotors is not one of the spec's I keep. I have had rotors bolt on with under 003" runout without any shimming required, but by far they all are over 005", some up to 008".
Thank you for the detailed explanation of your process.
Runout is a artifact of the original design which many aren't aware of.
I wonder if it's feasible to machine the used hubs to zero runout. Of course only if there's a need to replace wheel studs.
It appears thats what's done with new vehicles these days, as only rotors are replaced all the time during brake work.
Rich- Top
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Mark, I spoke to Bairs and they no longer sell the Used Front Hub with New Rotor assembly listed in their catalog and they no longer sell USA made rotors. Did you ship your rotor hub assembly to Bairs for rebuild whereby they riveted and turned your existing hub to a new rotor? And, would most local brake shops do this type of work? Thanks to all for your very informative replies,
He was unaware of the Corvette "oddity" of hub to rotor runout, and that they needed to be turned as an assembly.
When he set up the lathe to cut the rotors, he then understood.
If you decide to go to your local shop, you may have to explain why.
It's too bad we can't get USA rotors now. Joe was correct in his earlier post.... Import only now.
RichLast edited by Richard M.; Yesterday, 11:08 AM.- Top
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Gary,
Thank you for the detailed explanation of your process.
Runout is a artifact of the original design which many aren't aware of.
I wonder if it's feasible to machine the used hubs to zero runout. Of course only if there's a need to replace wheel studs.
It appears thats what's done with new vehicles these days, as only rotors are replaced all the time during brake work.
Rich
Another option with the front assemblies is they can be correctly turned on a brake lathe. A slight kiss cut once the rotor is attached will true them to -0- runout. I like not to turn a chip if possible.
The rears present more concern and brake lathes, unless an on-the- car type won't work.- Top
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I have yet to meet anyone who has actually tried it and can confirm. I don’t know if they would keep the runout low, or just cut the rotors to the wrong angle.Vice-Chairman (West), Michigan Chapter NCRS
71 "deer modified" coupe
72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
2008 coupe
Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.- Top
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