I noticed that all the brake rotors on my 68 have the rivets drilled out of them. Any problem with putting them back in? What is the best way to do this and minimize run out? Car has not been driven in years. I would like to turn them before I use new pads on them. What is the best way to approach this? Regards, Terry
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Re: Brake rotors on C3.
You can attach the rotors by tapping the rivet holes and installing flush tapered socket head screws. Check the run out and if excessive try rotating the rotor to a different position. -
Re: Brake rotors on C3.
Terry, usually the rears are the ones that have the rivets drilled out, and that is done to access the e-brake pads and mechanism behind the rotors. Since all of yours have been drilled, all four rotors may have been replaced.
Normally, the rear rotor rivets are simply left out after the e-brake repairs are made. Others with experience can contribute here, but I don't know that the absence of the rivets results in any additional runout once the lug nuts are torqued...nor will replacing the rivets reduce runout.
If you are doing this to return the car to its original configuration, I would probably send the rotors off to one of the rear control arm restorers, like Bairs' or Van Steel, to get correct appearance on the rivets. The rotors should come back with runout well within specs. This approach would be influenced by the fact that I lack the tools, equipment, and experience to peen the steel rivets properly.
The other advice that I might add is that, unless the rotors are really heavily grooved, I would not bother turning the rotors. The new pads will soon conform to minor surface grooving. Furthermore, after a few miles, the freshly turned rotors will look exactly like they did before you had them turned.
In the past, rotor turning was SOP in repair shops, but it is beginning to fall out of favor; it was a way of running up the repair bill, and also of guaranteeing that a brake job didn't come back with complaints. The downside is that every time you turn a rotor that has a perfectly serviceable surface finish, you sacrifice valuable service life for no benefit. Original rotors for these old cars are getting harder to find; I would try to preserve that remaining life as long as I could.Comment
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Re: Brake rotors on C3.
Air pumping due to excessive runout is a pretty common problem that is often associated with drilled out rivets. There are those who will swear that it is impossible to achieve satisfactory runout without the rotors and axles being turned as a unit. There are a lot of cars, mine included with no rivets that have acceptable runout, but be aware that this can be a problem. When I first got my 67, I found one rotor with over 25 thou runout. Needless to say, this caused an air pumping problem!Comment
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Re: Brake rotors on C3.
Ed, count me in the camp that says, when air pumping is a problem, the rotors should be turned with the hubs. It is likely that manufacturing imperfections on the rotor/hub mating surfaces will build runout into the assembly. The rotor can be turned perfectly true only to yield excessive runout when mounted back on the hub.
If the rotors are not riveted, then the machinist has to find some means to hold the rotor firmly in position on the hubs (lugnuts?). In fact, the rotors should be punch marked to insure that they always remain in the same position on the same hubs thereafter.
Modern cars I have seen no longer have anything holding the rotors in positon except the lug nuts, not even that token spring washer that was used for awhile. They were a PITA anyway; you only noticed them (and cussed them) when you had to remove the rotors.
The result is not always pretty when something changes the factory setup; my wife's luxobarge has excessive runout in the right front. There's no air pumping like on Corvettes...just a slight shudder on braking. The service manual says to try different rotor positions on the hub to get runout within specs. I tried that unsuccessfully; I think I prescribed my own medicine above.Comment
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Re: Brake rotors on C3.
Terry my original owner 95K miles driven 68 still has the original brake rotors and they have never been separated from the original hubs/spindles. I have never had a air pumping runout problem with the brakes and never had a rotor turned on this car. My orignal owner 160K miles driven 70 still has the original front brake rotors, but the rear rotors are not original. Back in 74 Chev dealership garage, largest one in Dallas at the time under the 50,000 5 year warranty removed the rivets to repair a wheel bearing problem. With this repair and then taken back for warranty rear wheel bearing repair on the other rear wheel I was set up for several years of excessive runout, air pumping, brake bleeding, rotor turning, more air pumping,etc. This all ceased when I sent my spindles/rotors to Bairs and had rotors rivetted to the rear spindles. I bought the tools to service my rear bearings and have really truley enjoyed running down the interstate and having excellent brakes taking the off ramps. Bairs can rebuild/repair the complete system on the rear, if you are going to keep the car and drive it, it will last you a very long time. Only wish I had known of their services for my problem when it occured. My 70's rear brake calipers always had new fluid in them from repeated bleedings to get the air out before Bairs repair.Comment
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Re: Brake rotors on C3, silicone fluid?.
Thanks for all the feed back. All my rotors look original and appear to have a lot of wear left on them. They even look recently turned? When I get around to it, I will put a dial on the rotors and check the runout. You can tell what the original positions were suposed to be because there are alignment holes. I will use the lug nutd to hold them in place and just spin the wheels and see what it reads. I could probably rerivet the rotors myself but it may be just as easy to send them off to one of the places you guys mentioned. I am glad the air pumping problem was discussed because I have heard about it but never new how common or real it was.
Any comments or recommendations on silicone break fluid? Sounds like a good deal but I have heard arguments about not being able to take the heat and air bubbles developing and breaks getting moooshy. That was a long time ago. Best regards everyone, TerryComment
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Re: Brake rotors on C3.
LOTS of folks have this very problem and have solved it as you describe. I think the later editions of the factory service manual prescribe this type of repair vs the "drill 'em out and leave 'em " method. I checked both my rotors with just lugnuts holding them and have about .003 runout which doesn't cause a problem. Also, the rotors are marked so that they always go back in the same spot if removed.
The rotors can be firmly attached to the spindles with screws (thread the rivet holes) and turned at a local shop vs sending them off and I would expect the same results as with riveting. Sending them out will, of course, yield good results, but may or may not be necessary.Comment
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Re: Brake rotors on C3.
I can't agree that the air pumping is associated with removed rivets. The lack or presence of rivets has no effect on runout. As stated MANY times on this and other forums, the rotors were riveted to the hubs simply for ease of manufacturing and transportation by GM. Nothing to do with controlling runout, one way or the other.
The reason that high runout is seen on de-revited rotor assemblies is 1) a substitute rotor was fitted, or 2) the original rotor was reinstalled, but not in it's original orientation.
A common mistake, in addition to the perceived need to turn original rotors as Chuck points out, is to fit a new rotor out of the box and expect runout to be within spec. The key to the whole 'mystery' and something I understand unique to Corvettes is that the hub WAS NOT necessarily machined true to the centerline of the axle. This means the hub can have a certain amount of runout. No amount of machining of a rotor (on it's own) will correct this, the two must be done as a pair. This is what GM did, and the reason they were riveted.Comment
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Re: Brake rotors on C3, silicone fluid?.
Thank you for all the great comments. I like to fix things right and I feel like I have a lot more insight about this mater. Still wondering a bit about the silicone brake fluid. I suspect it is not NSRS approved in 68 but it does have some desireable features. Really, the only good thing I can think about it is that its not corrosive like good old stuff. My understanding is that it won't absorb moisture like the standard stuff. But, even standard fluid has a limit as to how much moisture it can hold before the water starts to settle out and cause problems. Actually, if things are right, you shouldn't have much moisture getting in the lines anyways. Any comments on this would be appreciated. Regards, TerryComment
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Sorry for the "Delete"...Trying to be thorough.
Terry, rather than "spin" the rotor, I recommend the following procedure:
Mount your dial indicator on some hard, stationary part of the suspension near the rotor using a magnetic base. Position the indicator such that the stylus is near perpendicular to the rotor surface and on the pad contact area near the maximum diameter of the rotor.
Zero the indicator by turning the dial to place the dial zero on the needle tip, give the instrument a couple of GENTLE flicks to normalize it, and record the starting reading. Note: It is immaterial whether the small "tenths" dial on the dial face is zeroed; in fact, it is preferable to have the stylus about mid-range in its travel; i.e. a few tenths of an inch showing on the small dial.
SLOWLY turn the rotor (like a glacier, but not necessarily continuous movement ) through a full revolution, noting the deflection of the needle to the maximum positive and negative readings and record the readings. Add the maximum positive and negative readings together ignoring the plus/minus signs...the sum is your total runout
Repeat several times to confirm your result. After each measurement, check to see if your dial indicator has returned to approximately the "zero" starting reading. If it does not, you have either not returned the rotor to the starting point, OR, the position of dial indicator has been disturbed, and the last reading is suspect.
Your dial indicator will thank you.Comment
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P.S. Silicone Brake Fluid
Terry, there is extensive discussion on silicone brake fluid in the archives. It's like the choice between acrylic lacquer and urethane...some are fer it, and some are agin' it.
There are advantages and there are disadvantages. If you are converting a system already using glycol brake fluid, then you have to get the system fairly clean to make the conversion. The two types of fluid are not incompatible, but failure to get all the glycol fluid out of your system will compromise your result.
If you start out with a new clean system (e.g. after a complete restoration) with new lines, rebuilt calipers and rebuilt MC, then the decision is a no-brainer in my opinion. No more absorbed water, no more corrosion, no more brake problems (be sure your runput problems are fixed), and no worrying about spills on your fresh restoration.
The problem of entrained air has to be addressed before the fluid is installed. I haven't done it, but I understand that you have to heat the silicone fluid at low temperature to drive off the entrained air before installation. You also have to insure that you get the system bled well. With old Corvettes, that's hard enough to do with glycol fluid, but it is critical if you are using silicone.Comment
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Re: P.S. Silicone Brake Fluid *TL*
While the manufacturers of both glycol and silicone fluids maintain they are compatible, I suggest for best results treat them as mutually exclusive. You don't necessarily need new lines if yours are in good shape, flushing well with alcohol will get the glycol out - then blow out the lines with dry filtered air. Shop air that is suitable for painting is adequate.
It is essential to disassemble and clean the master cylinder and calipers. Reassembly must be done with silicone compatible lubricant. All traces of the glycol fluid must be removed from the system if future problems are to be avoided.
I have not heard of heating the DOT 5 fluid to drive off entrained air, but it might be worth trying. Pouring the silicone fluid down a guide like a clean dowel or screwdriver will reduce the air in the fluid, as will gravity bleeding of the system. Pushing the fluid through rapidly with high pressure will lead to air entrapment, so patience is in order when bleeding.
TerryComment
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Maybe Bairs reindexes the rotors before riveting?
Ever think it wasn't the riveting the rotors on but that Bairs checked the runout, then adjusted them or shimmed them to get them right?
After all, what would their reputation be if they just riveted them on in any positon with no regard to the runout?Comment
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