After almost two years of running this setup, my wallet decided it was time for ZR-1 BBK version 1.1. The current setup stops like no tomorrow, but as some of you know I've been fighting rotor cracking problems for a while. The current pair of rotors has held up "OK" I guess as they have about 4 events on them. They have the surface checks, but none that have made it to the edge and formed a crack...yet. Either way these rotors are getting too damn expensive to replace. At $300 a pair isn't just not worth it anymore, especially considering the C5 Vette guys can get NAPA blanks for their care for $29 each.
For a little history, the reasons I didn't go with stock Vette blanks from the get-go were as follows:
1. The offset of the Vette "hat" isn't quite what I need for ball joint/spoke clearance which isn't surprising since those weren't designed for FWD car. A 2-pc hat/rotor combo seemed to be better at the time since I could get the exact offset I needed.
2. I thought (at the time) the re-drilling the stock Vette rotors to fit my 5x100 lug pattern would get expensive. I was right about that except for the fact that the pattern doesn't need to be exact like I thought. The hub bore is what needs to be *exact* not the bolt holes. Hindsight is always 20/20 right?
3. I figured since these 2-pc rotors were massive for my car they'd last a VERY long time. WRONG!!!!!
OK, fast forward to present day and what I've learned so far and I know I could do it better and cheaper. Here are my thoughts/options:
Use a stock C4 HD Vette (J55 package) rotor up front. The HD version used on the ZR-1 and Grand Sport models were 13"x1.1" compared to my current 12.2” x 1.1” 2- pc rotors. I can re-drill the rotors myself and get a machined bushing for the difference between my center hub and the bore of the Vette rotor.
This would require me to move the caliper outboard about 3/8" which is the difference (radially) between the current 12.2" rotor and the new 13" one. That shouldn't really be a problem with my 17” wheels assuming the hat offset will work. FYI, The NAPA version of the Corvette J55 rotor is $59 which is about 1/3 of the price I pay now for the 2 pc blanks from Coleman Racing.
After a little more research, I discovered the stock Cobra Rotors (they share the same PBR caliper as the ZR-1 Vette and 1LE Camaro) have a shallower offset (closer to what I need) and are $20 cheaper than the Vette rotor from NAPA at $39 each. Ryan and I have figured that I'm currently spending $100 per track weekend just on rotors. If this works out I should be able to cut that number to one-fourth....$25.
OK, so let’s buy a Cobra rotor and do a little fitment experiment.
Last week I removed the 2-pc rotor for comparison to the stock Cobra rotor. I don’t have a shop so the kitchen table would have to do. Upon laying them flat, I was happy to see they were pretty close. After some measurements with my calipers, it turned out that the Cobra rotor is actually about 0.4” shallower than my current 2-pc ones. Well that’s good and bad. The good is there will be no interference with the spindle or ball joint. The bad is there could be interference with the wheel spokes. It’s too close to call w/o actually fitting the rotor onto the hub and seeing if there is in fact a clearance issue. I can use a small wheel spacer, but I don’t want to have to use one on track.
Next I made a template to re-drill the Cobra rotor using AutoCAD and modified the rotor at work. We actually have an old (really old, like 50 years old) drill press here at work. My template and our old drill press worked very well. Even using an el-cheapo 1/2" bit it wasn't *that bad*. I even beveled the trailing edges of the holes just like the factory ones.
Last weekend I removed a wheel and put the new Cobra rotor on for a test fit. Good news...it worked! At least with my street wheels that is. My track wheels have spokes that bend inward so they may not clear w/o running a spacer. I'd prefer not to run a spacer on track so I'll probably swap the tires between my street and track wheels and run spacers on the street.
Since the caliper needs to me moved outward, my current spindle brackets wouldn't work. They are welded in place so I really need to start over with another set of spindles. It’s a lot of work, but since I've done it before it's not that big of a deal. That and the fact I'll still have the old setup if a problem pops up at the last minute.
For the spindles Ryan and I went to LKQ in Clayton and I bought two for $50. I was off for the 4th and time for modifying them was at hand which brings us to the present photo diary of what it takes to put 13” Corvette/Cobra brakes on a Cavalier. Of course there is more work to be done, but here’s the progress so far.
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