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Do i have to tap my rotor and hub together on my c3 1976 i am replacing my rotors and the old ones are rivited together
 

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No, you can simply drill out the rivets and don't worry about replacing them when you install the new rotors.
Best,
Greg
 

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Do i have to tap my rotor and hub together on my c3 1976 i am replacing my rotors and the old ones are rivited together
If you are replacing the rotors and you are using original lip seal calipers, you will need the correct for any runout over 0.005 in. This will probably mean shimming the new rotors with shim stock on one side ontill a dial gauge reads less then 5 thousandths of an inch. GTR1999 says to tap them. Do so if you have the facilities to do so. If your going to replace the calipers too, go with O-ring calipers, they are pretty much immune to the air leakage problems the original lip seal designs have. You may have problems if you don't shim, ask me how I know. My O-ring calipers should be here by next week. As far as tapping goes,, with the o-ring calipers and run-out corrected, I'll be fine,, as far as just correcting for the runout w/o tapping, I personally think you'll be fine too.
 

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VBandP did my T/A's before I knew Gary. They adjusted run-out to .001", but did not bolt them back. However, they are marked , indexed, as to assembly to get them correct. They have been fine so far.
 

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I tapped and bolted mine up... Made shimming easy, and gives me peace of mind.

Why would GM rivet them together if they didnt need to be?
 

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Why would GM rivet them together if they didnt need to be?
So that the rotors don't fall off on the assembly line ...

The calippers hold the rotors in place when you for example take a wheel off, you don't have to drill and tap but it's nice to have the rotors secured so that when you take the calipper off to change pads the rotor can't fall off the hub.
 

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The rotors were riveted to the spindles and hubs then turned. The resultant finish had no runout and was perpendicular to the axle centerline. Replacing rotors or turning off the hub or spindle will not get this close. The finish may be fine but you'll have runout.
Bolting them in place gives the option of dialing in the runout to acceptable spec's and holding them there. Turning and using just the lug nuts does not.
 

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Gary,
when I took my rotors off three years ago I had to drill out the rivets - I assume these were the factory rivets. I found shims between the spindle and rotor.
Did they came from the factory shimmed and riveted or without shims ?? I would think if they machined the rotors assembled to the spindles there's no need to shim them in the first place....
 

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I can't say I ever found shims in a riveted rotor before? Doesn't make sense unless someone had it apart for some reason?
 

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I agree that it doesn't make sense.... maybe somebody had it apart to do some work... probably the same guy who bent the strut rods :rolleyes:
 

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The rotors were riveted to the spindles and hubs then turned. The resultant finish had no runout and was perpendicular to the axle centerline. Replacing rotors or turning off the hub or spindle will not get this close. The finish may be fine but you'll have runout.
Bolting them in place gives the option of dialing in the runout to acceptable spec's and holding them there. Turning and using just the lug nuts does not.
what kind of bolts do you use? thanks..
 

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I have the procedure above in the stickys. Shows the flat heads I use.
 

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The rotors were riveted to the spindles and hubs then turned. The resultant finish had no runout and was perpendicular to the axle centerline. Replacing rotors or turning off the hub or spindle will not get this close. The finish may be fine but you'll have runout.
Bolting them in place gives the option of dialing in the runout to acceptable spec's and holding them there. Turning and using just the lug nuts does not.

I don't quite understand your last statement there, Gary.
You certainly CAN hold a shimmed rotor in place with the lug nuts
to check for runout, indexing the rotor to minimize, and then take the
lug nuts off before installing the wheel over the shimmed rotor.
This is how I did mine, all shimmed to less than 2 mils runout ...
despite the fact that I also rebuilt calipers with the VBP Oring kit.
It may be nice to have the tapped rivet holes, but not necessary.

:buhbye:
 

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Dave,
I have played around with the rotors with lug nuts and then bolting on. I found the runout did change everytime I tightened and loosened the lug nuts as one would if replacing the wheel. The amount of change did vary but it was in the .003 -.005 range. If the runout was not within spec to start it could be all over the place. Since it's not uncommon to find up .010 runout in both USA and imported new rotors it's not the way I would do them.

Now I know the practice of replacing the rotors and using the lugs has been around a long time,( I do recall buying new GM front hub/rotors riveted for $99 too) and this has worked, but if you want to be sure then bolt them on and dial them in. It has worked for me and is worth the extra time in my opinion.
 

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I make them up from SS shim stock industrial suppliers sell. I use a hole punch to get a nice round ID hole.
 

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Dave,
I have played around with the rotors with lug nuts and then bolting on. I found the runout did change everytime I tightened and loosened the lug nuts as one would if replacing the wheel. The amount of change did vary but it was in the .003 -.005 range. If the runout was not within spec to start it could be all over the place. Since it's not uncommon to find up .010 runout in both USA and imported new rotors it's not the way I would do them.

Now I know the practice of replacing the rotors and using the lugs has been around a long time,( I do recall buying new GM front hub/rotors riveted for $99 too) and this has worked, but if you want to be sure then bolt them on and dial them in. It has worked for me and is worth the extra time in my opinion.
Well I'm not going to argue what works best for you, but the lug nuts worked out fine for me.
Let me ask you this, though ... do you know if the runout STAYS in spec
AFTER torqueing the wheel in place ? Perhaps the same differences you saw
when using the lugs alone. Even bolted, I would want the nuts torqued down, also while indexing.
Ideally, I guess you would want to cut the center out of a wheel
and use that as a torque plate while measuring the runout.

For shims, I used Aluminum soda can stock ... sometimes sanded down thinner.
Remember that a shim thickness at the stud will provide much more
change to runout at the edge of the rotor.
For very small adjustments, I used a small square of duct tape.
When compressed, it gave about 1 mil thickness of shim ... and stays in place.

Call me Bubba ... I don't care. :smack
 

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Dave,
I have played around with the rotors with lug nuts and then bolting on. I found the runout did change everytime I tightened and loosened the lug nuts as one would if replacing the wheel. The amount of change did vary but it was in the .003 -.005 range. If the runout was not within spec to start it could be all over the place. Since it's not uncommon to find up .010 runout in both USA and imported new rotors it's not the way I would do them.

Now I know the practice of replacing the rotors and using the lugs has been around a long time,( I do recall buying new GM front hub/rotors riveted for $99 too) and this has worked, but if you want to be sure then bolt them on and dial them in. It has worked for me and is worth the extra time in my opinion.
There is not only runout on rotors but there is an unbelievable amount on hubs and spindles! I just machined (faced) some hubs and they are not even close to being flat and square. I removed .012 off of one before the whole surface cleaned up.

I am getting ready to do some brand new rear spindles and you can see that they were machined with the stud and rivet holes in them and the interrupted cut left a wave on the backside of every hole.

I would do as Gary suggests. It might be a little more work but it's you BRAKES! Do it once, do it right.

Edit: you can buy the shim washers and c'sink screws at McMaster-Carr (No I do not have any connection with McMaster-Carr):laughing:
 

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I mailed mcmaster-carr but they don't sell to overseas customers anymore and there is not much variety in the bolts and shims we can get here :down:
 
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