cygnusx1 Posted September 16, 2008 Share Posted September 16, 2008 I've got the AZCar 12.2" Wilwood Brake kit all around. It has seen two track days and about 7,000 miles of mild street use. The brakes have been excellent at stopping the car like a parachute. My problem is that the front rotors needed to be cut from day one. Dave at AZC made it perfectly clear that they needed to be cut from first use. Shortly after having them cut, and bedding them in according to BAER brake bedding procedure, they began to shimmy after a track day at Watkin's glen. I had them cut again and re-bedded. Now after a few thousand miles of casual street use, they feel OK until they warm up. Once they warm up, they shimmy pretty badly...but only when they warm up. Is this a classic symptom of uneven pad deposit or are the rotors warping when they warm up? I tried re-bedding them with no difference. I am about to order a set of brand new authentic Wilwood replacement discs from Summit but I wanted some opinions first. The pads I am using are I believe the Wilwood "J" compound but I am not sure what Dave threw in the box when I bought the kit. They make very little dust, no noise, and stop much better when they are hot. Maybe they are the Ploymatrix "Q" compounds. Quote Link to comment Share on other sites More sharing options...
jt1 Posted September 16, 2008 Share Posted September 16, 2008 Usually you can see an uneven pad deposit on the rotor, it will look splotchy and streaky. I have never had a problem with the genuine Wilwood rotors. Normally I run the GT48 series, they last longerand normally wear equally with PF01 pads. You might check prices at pitstopusa.com. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted September 17, 2008 Share Posted September 17, 2008 Have you contacted Dave @ AZC? He's usually quick to solve any of my problems. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 17, 2008 Author Share Posted September 17, 2008 I did when I first bought the kit and when they warped the first time. I think it's just time to replace these rotors. The standard answer to out of round rotors is to cut them. I don't feel comfortable putting a third cut on these so I am just going to go with a new set from Wilwood. Before I install the new rotors, I am going to put a dial indicator on both the rotor and the CNC hats to make sure the hat or hub hasn't warped. Wilwood also recommends installing the rotors and checking runout, then indexing and shimming the rotor/hat at the bolt circle, to get it as straight as possible. I think I need to spend some quality time in my front fenders with a dial indicator to figure this all out. Mechanical stuff is so refreshing after finishing up the haywire EDIS/MSII project. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted September 17, 2008 Share Posted September 17, 2008 Mechanical stuff is so refreshing after finishing up the haywire EDIS/MSII project. Oh I hear you on that one! Mechanical > Electrical. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 17, 2008 Share Posted September 17, 2008 I'd try a different pad with the next set of rotors. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 17, 2008 Author Share Posted September 17, 2008 Jon, Yeah but it's good practice to bed new rotors on used pads. No? I think I'm on "Q" compound and that fits with my use pattern. 99% street and a track day once in a blue moon. What compound would you recommend for street? I use ceramics on my Subaru for DD and they make no dust and no noise but their bite just isn't "sharp". I really liked the feel of the Axis Ultimates I used to run in the subie but they made way too much dust for a DD. I wonder of the PF Ceramics might work on the Z for street use. Not the best bite but a good working temp range and no dust. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 17, 2008 Share Posted September 17, 2008 I've had very limited experience with pads in the last seven years or so. I had a pad I liked, then I stopped racing. Other than that I've been running stock pads on my GMC truck and my Subaru Outback, so I'm not the right guy to ask. Based on what I've heard from friends and people here, I've purchased Hawk Black pads for my own use. I think for street I'd probably try the Hawk HPS+. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 27, 2008 Author Share Posted September 27, 2008 OK so I took some late night time, went out to remove the front wheels to get the dial indicator on the rotors and hats. I already have the new rotors from Wilwood but I wanted to do some CSI work before I swapped them. The drivers side rotor is twisted by about 0.005" across it's face along a radian, at it's worse point. So runout at the outer edge is around 0.005" on both sides of the rotor, and runout at the base of the swept area is about 0.003". The passengers side rotor is out the same way but about 0.010" total at the outer swept area! I am sure these numbers get worse when the iron heats up. Both AZC hats are running within +/- 0.0005", while mounted on the hub, which is what I expect for a CNC machined aluminum part. So enough talk about pad material build up...it's a warped rotor. Period. On another note, I noticed that the passenger side pads are worn about 10% more than the drivers side pads. Maybe I need to open up and back flush my front brake lines and factory prop valve and splitter. Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted September 27, 2008 Share Posted September 27, 2008 I suspect I'd find the same results if I were to put a mic to mine. I have the same set up with the same issue when warm.... Where did you pick up your new rotors? Do you mind revealing what you paid for the pair? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 27, 2008 Author Share Posted September 27, 2008 I bought the replacements from pitstopusa.com as JT1 suggested but I didnt go for the more expensive GT48 series. I bought the direct replacement Wilwood HD Curved Vane series for $83 each. http://www.pitstopusa.com/detail.aspx?ID=71458 You need a left and a right one. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 27, 2008 Author Share Posted September 27, 2008 I bolted on one new rotor from Wilwood and indicated it. It is off by about 0.015"! They claim flat and straight to 0.001 on the website so it must be warping when I tighten the 8 bolts to the hat. The hat indicated flat on the outside. I am going to see if the rotor is warped when I take it off the hat by laying a straight edge on it. I also have 0.001" and 0.002" thick shim washers that I can use to try to clock and shim the rotor straight. The whole thing seems strange. I am beginning to see the value of floating rotors. Quote Link to comment Share on other sites More sharing options...
Clifton Posted September 27, 2008 Share Posted September 27, 2008 I've already turned one set of rotors ( 5lug kit) and they are warped again. This is on the street car too. When you indicated on the hat was it the rotor mounting surface side? I was considering just buying a new pair of rotors but I know they will warp too. I need to check my hats without the rotors on. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 28, 2008 Author Share Posted September 28, 2008 Funny you said that.... I took off the rotor and checked the hats from the inside, where the rotor bolt circle is, and it was off by around 0.008". For some reason I was reading dead straight on the outside of the hat with the rotor in place. Once the rotor was off I did the insied of the hat. So I decided to shim the four bolts that hold the hat to the hub. I added precision stainless steel shims that I had bought and got the hat to within 2.5 thousandts. Then I mounted the new rotor and it was within 0.003". I am going to do the other side like this, drive it, and then have them lightly cut after a few heat cycles. Verdict: Either the hat is warped from AZC which I doubt, the Z hub is off ( I didnt check it but I doubt it ), or the four hat bolts, when tightened, warp the hat. The hat has waves in it once bolted. I think the four bolt circle is just not enough to keep the hat flat. The rotor should "ride" over and smooth the waves anyhow. NOTE: The hat fits kind of snug around the hub center and there are fillets that could possibly interfere causing the hat to NOT seat flat on the hub flange. When I first installed this kit, I filed a bit of extra room into the hats for fillets that are cast into the Z hubs. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 29, 2008 Author Share Posted September 29, 2008 I ran out of shims so I decided to cut up some feeler gauges. I managed to get the passengers hub dead straight. As a result, the rotor has only a 0.001" runout on the pass side. Two of the four hub/hat bolts needed 0.004" shims. I think that AZC should add this to the instructions. Using a dial indicator, shim the aluminum hat, between the hub and hat, as straight as possible before mounting the rotors. Had I not shimmed the hats, I would be cutting 0.030" off of a brand new rotor to get it straight! Quote Link to comment Share on other sites More sharing options...
jt1 Posted September 29, 2008 Share Posted September 29, 2008 Interesting. When you do the other side, can you check the back of the hub where the hat bolts up? It seems one or the other must be off to cause the runout. John Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 29, 2008 Author Share Posted September 29, 2008 I couldnt get my dial indicator close enough to center to accurately check the hub. It's the only unkown at this point. It could be off, but from putting on brand new stock sized powerslot rotors in the past, and not having to cut them, I assume the hubs are probably straight. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 29, 2008 Author Share Posted September 29, 2008 I just came back from a test drive where I went easy on the brakes. I warmed them up gently with some 40-10mph medium stops and normal driving. The rotors feel SILKY smooth! Hands off braking galore. No more cutting up brand new rotors. !!SHIM THE HATS!! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 29, 2008 Share Posted September 29, 2008 What is the perceived advantage to cutting the rotors vs shimming the hats? Quote Link to comment Share on other sites More sharing options...
mark Posted September 29, 2008 Share Posted September 29, 2008 What is the perceived advantage to cutting the rotors vs shimming the hats? I was wondering the same thing. If the rotors are straight after they are cut, all should be good. Same thing with shimming, all should be good. However if the issue was the quality of the rotors and they were cut or shimmed, the probem would return after repeated heat cycles. Keep us updated on this. Now I need to do the same with my set up and find what is causing my vibrations after a few track sessions. Quote Link to comment Share on other sites More sharing options...
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