Bob Heine

First, I apologize for the sarcasm in my previous post but you really did set yourself up for it. Even with the calipers off, I've never had a Corvette rotor fall off and I'd be hard pressed to make it happen without a rotisserie being involved. Might happen with a Fiat or some other European car that uses bolts to mount the wheels.

At 150 miles per hour, your 27.1 inch tall tires are turning just over 2,000 rpm and I'd bet the roundness of the tire is more important than the shim under your rotor. I agree that shimming is not the ideal solution and if I were planning a record run at Bonneville or 500 miles at Daytona, it would be completely unacceptable. However, there is a big difference between home-made shims and specialty shims.

Raybestos, a reputable manufacturer of auto parts, manufactures steel shims whose mating surface is tapered to correct .003", .006" or .009" runout. The full circumference of the mating surface of the hub and rotor is supported and you are not supposed to stack them. Rockauto.com sells them for the C3 Corvette for $12.29 each.

I think shimming the rotor this way is no more dangerous than using spacers to mount a wheel/tire combination for added clearance.

Here's what the shim looks like (the notch indicates the high spot and the ten holes allow the high spot to be placed fairly close to the lowest spot on the hub (at or between the stud).


Here's the catalog entry for the C3 shims:
http://www.rockauto.com/catalog/rafr...BA90903-749474

None of this is of any use to you in this case. Your rotor for sure and maybe even your hub is messed up. Your best solution is to buy new hubs and rotors. Auto manufacturing is full of compromises. As I understand it, the Corvette rotors were riveted to the hubs and then trued. The hub surface isn't critical in that process because minor runout is corrected in the assembled unit. The problem arises when you put a new rotor on the original hub. I would expect new hubs to be true so you should have no problem with runout. However, I would suggest you forgo hot rivets and the peening operations on your new hardware unless you plan a second hub/rotor truing operation.

wombvette

I am still not totally convinced that just turning the rotor bolted to the axle insures no run out. Yes it will be no run out on the hub and rotor, but the shaft can still wobble the amount that the bearing play allows. I think they are great for modern sealed no clearance bearings, but not necessarily a fairly loose corvette rear.

...Roger...

I wonder the same thing,but because Noonie and others have used this machine with good results the shaft must not be wobbling.

In the rear assembly ( C3) with weight on wheels on the ground what part of the bearings are being used ?
Is the top portion of inner and outer bearings bearing the weight ?
Or is the top of the outer and the bottom of the inner bearing the weight ?
Or because of the "taper" design is the entire bearing wedged into the races and bearing the load ?

I've always wondered why the bearings weren't designed like diff pinion bearings and put under a preload.

One other thought-If the spacing between the inner and outer were was doubled the end play would be far less critical.JMO

noonie

Bearing play always comes into consideration as mentioned in previous posts, but a simple example is the front spindle. More often than not, they are a bit loose after use and there are no special rotor considerations there. Pumping every revolution is the big concern. It's not a perfect world out there.
On car turning is still the best result short of pulling the rear spindles.

If you want a basic primer (or at least Timken's viewpoint) to the bearing loading, shaft interference etc, you can download Timken's engineering design catalog. Heat, duty, shock loading etc. It goes into all that detail that has been opinionated here a few times.

Mike Ward

You're right Wayne. The braking surface may be true to the face plate of the rotor (wheel mounting surface) but there's no way to machine out the bearing free play. In my mind it's two separate operations that give a cumulative result.

I believe this is the case when the car is static. Once it starts moving- especially accelerating or braking under bumpy conditions-, the load is transiting from one bearing to another and any/all faces are part of the contact surface. As to why it wasn't designed a different way, your guess is as good as mine. In retrospect, there's lots of things that could have been done to make servicing easy but the original design was 'sealed for life' ie no need to disassemble in the field.

We also could speculate over the subject matter here and wonder why the rotors were not intended for field replacement either.

I guess being a pioneer design for disk brakes/fixed calipers/four pistons, all attached to four wheel independent suspension has it's price.

I still think it's a design that equals or surpasses some of the stuff on modern cars despite being more than 50 years old.

wombvette

I will try to find time to read up on what Timpken thinks, but as I see it, unless the rear bearings are zero clearance there is no way to machine the rotors for zero run out with that machine. It may be negligible in most cases, but with a well worn or loose corvette setup, I think it could be significant, and that is compounded by it being driven with a shaft that exerts loads at variable angles and bindings of U-joints. Again, it all may be negligible in practice.

Mike Ward

Wayne, I think you've misunderstood how this machine works.

...Roger...

I had to watch the vids a couple times and I'm just assuming the computer is figuring for centerline of the spindle.

dtamustang

I'm so glad I don't have to deal with customers anymore.......every now and then i think about opening a shop again.then i get a hard shot of reality and the thought goes far far away

Chromie69

Hey guys..just wanted to interject one major point on machining the rear rotors..if you take your vette to a shop that does not work on them make sure they either jack up both sides of the rear or remove the outer drive shafts from the outer hub..I had a major heart attack when I flipped the switch on the pro cut and forgot about rear u joint bind! The car almost jumped off the lift..well not really..just scared the peeps out of me..I ended up removing the drive shaft bolts..takes 10 minutes..machined out nice ...just thought I would mention it as an fyi..don't want any flying vettes out there..you all talking about runnout from what I remember of the trainer that came out and showed us how to use the machine said that if the bearings are to whacked out it will not setup..it will click and show re try..it will not remove bearing runnout..it will make the hub and rotor no run out..so the question is how tight are your bearings as that is the only run out after this machine is done..

Mike Ward

Interesting info. I take this to mean that the machine assumes that the wheel mating face is perpendicular to the axle. If not, the varying torque load to turn the spindle 360* will cause the machine to fault.

Chromie69

I am not sure how it calculates the adjutment procedure..I do know it can only adjust so much..so if the hub and rotor are warped to much or the bearings are out of adjustment the machine process wont be correct..you can force machine which I have seen a guy do once and he cut half the rotor off..that's another story though..it adjusts for run out with little wheels on the outer part of the hub that turns the rotor..I can take a pic of it working if you guys are real curious..maybe a video of it..don't have to have it hooked up to a car to do so..oh I do know also the the accuracy can be adjusted to fine or coarse..meaning how much run out it will compensate for.

Rockn-Roll

I received my new hubs yesterday, but didn't have time to do anything with them until now. They came with lug studs installed, so I don't have to worry about out-of-tolerance fit, heating up the hub, etc. They also came with new bearing races installed...again saving me from heating up the hub...nice. The package also includes new Timken bearings and seals, washer and spindle nut...again nice to have everything I need to install the hub/rotor onto the spindle...even new grease retainers and bearing caps.

OK...they look nice...all shiney and newly machined, but are they within tolerance? I fit a rotor onto the spindle with the new bearings and snug the spindle nut...setup my dial indicator and see only .002" of runout at the outer edge...really can't really expect any better.

I pickup some 7/16-20 nuts to temporarily attach the rotor to the hub and check it with my dial indicator and see .003" of runout...again...can't really expect any better. Looks like my project is finally moving forward again. I still plan on drilling holes in the hubs and installing rivets, but I'm not going to do it with a hand drill or even a drill press...I'm researching a machine tool...most likely a knee mill. I hope to move my project out to Oklahoma and finish it up at my uncle's shop.

I looked at those vids of the on-car-lathe...sweet. I wish the shop that hacked up my rotors used that...then I'd still have my original hubs and rotors.

Chromie69

Well that's good news..to bad you had to got thru heck because of a bad cut..next time if you need it done hunt out the pro cut..you wont be disapointed..still need a tech with a brain but we are out there!

Mike Ward

At the risk of invoking more Mr. Nasty comments from my fan club, I still don't understand why you didn't use the old hubs with new rotors.

Chromie69

Mike you crack me up!

Rockn-Roll

Because when I drilled out the rivets per the advice from Corvette Care some of the holes got off-center and removed hub material outside of the rivet holes...causing the hubs to be unbalanced. One of the holes is so bad the rivet would most likely not stay in place.

I think if Corvette Care really cared and was sorry for what they did then they would have used their drill press and removed the rivets for me...don't you think? I mean...it's not like I didn't offer to pay for them to do it...I would gladly pay for the labor...heck I already paid them for everything else...they simply didn't want to do anything to fix the problem.

Well...like I said in my last post...the new hubs are good...the new rotors are good...and I can finally get my car back on it's wheels.

willem wallace

Thank goodness you didn't have that shop tackle an engine overhaul, you'd probably have been "commited" by now!

Rockn-Roll

Update:

When I checked the first rotor and hub I measured the runout for all 5 possible orientations of the rotor onto the hub. The best I got was .003" and the worst was .006"...indicating that the rotor had some runout as well.

But, when I checked the second hub and rotor I got nearly identical readings...all between .007" and .008" runout. Which means the other rotor had almost no runout. So, what I did was swap the rotors and was able to get .004" runout on one hub & rotor set and .005" on the other hub & rotor set. I think this is the best I'm going to get without a lathe.