I finally purchased a dial indicator and magnetic mount (Harbor Freight) and measured my runout on the fronts. Looks to be about .009 or so on the outer edge. Too much according to my Haynes manual (.005). I also checked overall thickness with a set of calipers and I'm getting close to the 1.23" minimum. Is it worth it or possible to have these turned? If so, how do you find a good shop (no Bubba's) to do this without screwing them up? But...I did some searching online and it looks like I can get a set of Delco fronts for about $35 apiece. Seems like it would make more sense to just replace? Thanks guys.
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1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
Vette(s): black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion
Joined: 8/22/2006
Posts: 1094
If they are close to the minimum Id go ahead and get the Delcos. Although they are Delco, dont assume you will not have runout. You will still have to check runout and "clock" them and/or shim them to get minimum runout.
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Joined: 11/8/2003
Posts: 19509
I agree. For the price, it's not worth having the old ones turned, only to find they are too thin, AND the guy that did them screwed them up....so you have to buy new ones anyway. Be sure to CLEAN the new rotors in hot soapy water, with a good stiff brush, and then blow dry them. This will get all of the metallic particles off of them, and make it easier for the pads to bed in.
____________________________________ Joel Adams C3VR Lifetime Member #56 My Link
Thanks guys! I'm going to order the Delcos. A couple more questions, though: what's the method for drilling out the rivets on the originals (e.g. drill bit size, go from outside or inside, etc.?) Assuming this is something you don't want to do with the hub mounted on the spindle?
The runout thing has me concerned. Is this tricky to get right? Chip, I'm assuming by "clock" you mean rotating the rotor to different stud positions to try and minimize the runout? And if you can't get it within spec then you need to shim. It looks like there are tapered donut shims available that go over all the studs (spendy), but then there were also examples on the net in which guys just used hardware store shim material over one or more studs. This is pretty complicated and my manual does not cover it - thanks again for the help.
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1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
Vette(s): 1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top
Joined: 5/18/2010
Posts: 1518
Dave the shim thing really isn't that hard..use the dial indicator to find the low spot..mark the rotor at the low spot and put a shim under that spot on the wheel stud..I've used soda cans for this and it works fine..just cut a circle out of one and cut a hole in it so it goes around a wheel stud....this works to a point but it should get the run out down to where its in spec..if they end up needing fine tuned like I like them to be get them cut on the car with a pro cut machine..Google it..there's plenty of info out there on these things...the rivets are easy..drill bit size isn't that important..just go big..I think the last time I used a to 3/8 bit..cut the head off with that then used a punch to push the rest of the rivet out..don't try and drill all the way thru the rivet...its a 5 minute job no problem..and yes do it off the car on the front..kinda have to do them on the car on the rear..have fun!
|UPDATED|11/13/2011 5:46:00 AM (AZT)|/UPDATED|
____________________________________ My first parade at Carlisle 2010
Vette(s): black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion
Joined: 8/22/2006
Posts: 1094
This really isn't that bad of a job and it certainly ain't rocket science. The rivets can be drilled out on the car or you can remove the hub and use a drill press but it is a bit easier if you remove the hub. Either way try to be accurate with your center punch and start with an undersized bit to drill through the center of the rivet then progress to a larger bit. once you have progressed to the larger bit and the head of the rivet has been removed and only the barrel remains in the hole you can drive the rivet out with a punch and hammer. Even though the head of the rivet is gone the barrel is swedged against the hole in the rotor and may not want to come out willingly. Once you get the hub and rotor separated you can clean up the face of the rotor before putting the new one on.
Yep, Ive seen the tapered rotor shims online too and they are really proud of them $$. I used regular old .002 stainless steel shim stock form a local industrial supply on mine, and cut the shims so they approximated the radius of the outer and inner edge of the rotor and punched a hole in the appropriate place so that the shim would fit over the lug nut stud. If you cut the shims just right you can put them on neighboring studs without overlap if you need to or cut a double one if needed.
With the rotor mounted on the car you clock the rotor to all 5 possible positions and see if you can get runout within spec and if not, then start with the shims. I used a felt tipped marker to mark the end of one studs when clocking and beside each of the holes Id write the runout when that particular hole was on the marked stud. You will have to securely bolt the rotor to the hub each time you move to a different position, use at least 2 or 3lug nuts so your readings are accurate. Get as much runout out as you can by clocking and then start with the shims. Mark the rotor at its lowest point and use shims to bring it up. You may have to put the shims on more than one stud and this gets a little tedious. Once you get the shims right you can just leave it right there with the rotor itself holding everything together or you can get industrious and bolt the rotor to the hub, its your choice but bolting insures that everything is going to stay in place. Ive attached a link from an old post with some pics that may be helpful. The link is not showing as clickable with the new forum software for some reason so you may have to copy and paste into your browser. Sorry for the long post but you guys know I'm long winded.
Dave, I used colbalt bits to drill out the rivets. As was mentioned the rotors should just be replaced. The run out will need checking as was mentioned. It does take time and patience to dial everything in. The pop can shims work really well. I fortunately have a cannister of various size washers that are also different thicknesses. A guy that I knew worked at a place called Freeway Washer. He put together a major assortment of washers that were brass, steel, copper, and stainless. I find it very valuable at times. And always recheck with the rotor secured.....as was mentioned. I marked the studs with different color marking paint pens to know where I was. And you more than likely need to use more than one shim.
Vette(s): 1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.
Joined: 5/18/2004
Posts: 6807
I drilled out my rivets with ease - soft stuff. The replaced with deco replacements and metallic pads. Bled the brakes and they're better than new.
As mentioned, rotors these days are cheap enough - the cost of turning them almost isn't worth it...
Just my 2Cts
Good luck!!
Paul
____________________________________ LukesVette Homepage Veteran of Operation Iraqi Freedom
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Thanks guys! This is some great information and I appreciate hearing about all the tricks and procedures you all used. I feel a lot better about this little project now. I ordered the two Delco fronts last night from Amazon. We recently bought an Amazon Prime membership - ended up getting free two day shipping on these cast iron beasts! Can't beat that.
Bad news is I'm only tackling the fronts for now. Assuming I can get a hard pedal after I bleed I'm going to call it good and mess with the rears next winter -- too many other projects (and stuff to spend money on) this winter. I had the rear wheel bearings replaced by a Corvette shop a few years back (very few miles on it since then) so I'm hoping I'm good.
Thanks again!
____________________________________
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
Well I took the day off today for some chores which included some time this afternoon/evening trying to shim those rotors. After several hours I ended up getting both (front only) to about .003-.004 runout. Does that sound pretty good, or should I keep trying? I used brass shim sheet from the hardware store. It has .001, .002, .003, and .005 sizes in 3"x4" sheets. I still have the .001 left - I probably could add in a bit of that over one or two of the studs to try to get that last little bit, but I had to walk away for awhile....
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1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
Vette(s): 1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top
Joined: 5/18/2010
Posts: 1518
Have you torqued the wheel on yet? If not do that on and off a couple of times to make sure everything is crushed into place..take one more measurement and see where you are..be carefull that you are not measuring any bearing play too..you're getting down to the really close stuff so anything can be a factor in a change in runnout..make sure all the lug nuts are torqued the same when you check the run out...like I said earlier..I like them as close to 0.000 as possible..just know any runnout you have now will get worse once you heat them up..I guess I'm assuming you are going to drive this car hard once its all done..the number you have is teter toter hand...if you have time get it to the lowest number..have fun!!
____________________________________ My first parade at Carlisle 2010
Vette(s): 1982 C3 Collectors Edition 44000 miles, sat in the sun most of it's life, My wife purchased it for me for fathers day in 2007 from her girl friend that had it for 19 years. It is on the road again. I'm retired but it is now my daily driver.
Joined: 10/17/2007
Posts: 2008
Just for info I saw a test on the stopping power of turned rotors over new ones. I thought I saved it but apparently not. Anyway it demonstrated that the grooves from turned rotors (all most all turned rotors do some more course than others) can significantly reduce stopping power. I do not remember exactly what it was but it was over 30%. I'm thinking it was closer to 50% in some cases. I think that would be way more than what a little run out would cause.
If anyone knows about that video it could be a good link to let everyone look at. Basically if you have your rotors turned make sure it is a real fine slow turning. The less grooving the better. Then sand off the tops of the grooves. If you do not what happens is the grooves move the disc (like a record needle on a record) when they meet the maximum they jump and restart the process over. Turning the jump period you have not breaking power.
Vette(s): 1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top
Joined: 5/18/2010
Posts: 1518
I remember that one!! Don't remember where it was..yeah quality rotor machining is define a big problem..its only going to get worse..shops are cutting time on everything which makes guys work faster and care less about quality..don't machine them unless you have to..the run out is important for caliper seal issues but it may be just a trade off.
____________________________________ My first parade at Carlisle 2010
Vette(s): 1982 C3 Collectors Edition 44000 miles, sat in the sun most of it's life, My wife purchased it for me for fathers day in 2007 from her girl friend that had it for 19 years. It is on the road again. I'm retired but it is now my daily driver.
Joined: 10/17/2007
Posts: 2008
Yes I really wish I could find that video it was an eye openner. The more I think about it the reduction in breaking power do to what is normal rotor machining process was over 50%.
I know after I say it I just desided that I would purchase new rotors. Doing what you needed to do to give you quality machining would be as expensive as rotors. That is if you could get someone who new what you were talking about. I did a YouTube search and could not comeup with anything do you remember how long ago that was?
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Joined: 11/8/2003
Posts: 19509
Most, if not all, NEW rotors are mill finished, not turned, so you start with a perfectly flat, parallel surface on both sides. Using a lathe, whether stand alone, or on-car, will put small grooves in the surface, very similar to a record album. The slower the final cut is on the rotor, the finer the grooves are...if the final cut is fast, it leaves larger grooves, and makes the pads want to jump around a lot. Yes, the pads will want to follow the grooves when the brakes are applied...no doubt aboot that. That's why we always use a sanding disc to knock the grooves down while the rotor is still installed(& turning) on the lathe. This gives us a more uniform surface, so the pads won't have as much of a groove to try to follow. I don't guess I've seen the video...might be interesting. I think the variables would need to be called out tho...how were the rotors turned, at what speed, etc. Besides, testing braking distances on freshly turned rotors, with new pads, is kinda misleading, anyway. Pads and rotors need to be burnished, or bedded in, before making any hard stops....that's just common knowledge. Do ya'll have any idea who did the comparison video?
____________________________________ Joel Adams C3VR Lifetime Member #56 My Link
Vette(s): 1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top
Joined: 5/18/2010
Posts: 1518
Yeah that's about it..its hard to see but it actually moves back and forth to double cut the rotor so it does a fast cut and a slow cut at one time but only removing the same amount of rotor material as doing a single cut..it does leave a clean finish as long as the bits are good..the people that made the comparison video made rotors and pads..can't remember the company name but that's where it came from..it was fairly old as it was talking about ABS as something new.
____________________________________ My first parade at Carlisle 2010
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