getZ Posted October 10, 2007 Share Posted October 10, 2007 I was checking the deflection of my new AZC brake setup and it is a shade out. Driver side was about .2mm and the passenger was just inside the Datsun spec of .15mm at .12mm. I know people have just had the rotors turned, but isn't it easier to shim the hub distance to the hat or would this cause any problems? It seems safe enough since the shim distance is really small. Even if it were at 1mm it seems safe enough if you added two .5mm shims to the middle positions. This is what I did: Say there are four bolts attaching the hat to the hub. Zero the dial indicator at the 12 o'clock position at the outside edge of the rotor. Spin the rotor around and see how much travel the indicator sees. In my case the 6 o'clock position was the furthest in and 12 o'clock was the furthest out. I added a .1mm feeler guage to the 6 o'clock position and my deflection dropped from .2mm to .08mm, I figured a a slightly bigger shim would have taken the deflection down even futher. If you are really meticulous I suppose you can even add .05 (half of the 6 o'clock position) to the 3 and 9 o'clock position. Anybody try this before? I was going to use shim washers (if I can find them) instead of cut up feeler guages just to hold them in there better. Quote Link to comment Share on other sites More sharing options...
GrommitZ Posted October 10, 2007 Share Posted October 10, 2007 I've done this with my 300zx vented rotors. My machinist says that several old Corvette racers shimmed their rotors. I shimmed them to get the run out(deflection) close, before handing them to my machinist who reduced the run out further down to .001-.002". I did use half height shims in the 3 and 9 o clock positions to minimize warpage. In the future I will not bother with shims since the 300zx rotors are so cheap. I'm surprised that your .1 mm shim only reduced run out by .12 mm. In my experience, a .1 mm shim should shift run out by .3 - .4 mm. Are you sure you didn't over correct the run out? If not, then I suspect you're bending your rotor hat. Geometry should tell you that the reduction in run out should be at least 2 to 1. If I had your setup, I would be more careful since the aluminum hats are malleable and more expensive. I would first rotate the assemblies on the hubs to find the lowest run out. You can also rotate the hats relative to the rotors. Also, I would check your rotor to make sure the thickness is consistent. My machinist also reccomended locktite for the hub bolts. If the assemblies get close to spec, I would try them out on the road to see if they settle a bit. Have you tried calling AZC? Quote Link to comment Share on other sites More sharing options...
getZ Posted October 10, 2007 Author Share Posted October 10, 2007 When I get the shims I'll post some pictures. I'm pretty sure of my measurements. I can take the hat assembly off and measure them on a granite stone, but I'm pretty confident it is not the hat assembly. I don't think the tolerances on those old hubs were very good. After all, they are 70's technology. I agree it should not be a 1:1 change because of where I am measuring (on the very outside of the rotor) versus where I am shimming (on the hat to the hub), but I didn't make this up. I actualy measured it. Quote Link to comment Share on other sites More sharing options...
buZy Posted October 11, 2007 Share Posted October 11, 2007 Mine had deflection too. .008 -.015 inches of runout. Rears: We faced the hub face surfaces as AZC recommends and shimmed between hub face and rotor hat using brass shim stock, the best we could achieve was .006. Then ran the car. Braking very smooth. Then to experiement removed the shims and ran the car. Again smooth braking doing multiple stops from 130 heating the brakes etc. Fronts: .008 -.012 inches of runout. Ran it as is. Again no problems at all. Perfect really. After break-in of 300 street miles turned the rotors for kicks. Final runout .006. In my opinion......, Unless your very seriouly racing its really not an issue at all. Before you shim and do all that work bolt it up and just test run the car. It doesn't add up on paper and math but I willing to bet your measured runout just like mine won't be noticed. At least that was my experience. This package is kickass stuff. Brian Quote Link to comment Share on other sites More sharing options...
getZ Posted October 11, 2007 Author Share Posted October 11, 2007 I didn't think the run out being slightly out of what manufacturers specs would be that big a deal. It was more an excercise of just doing it and going over the whole process, after seeing a few compaints about to much deflection. Quote Link to comment Share on other sites More sharing options...
MrFancypants Posted October 11, 2007 Share Posted October 11, 2007 I dont understand why you would need to shim them if you are using 4 piston calipers? As long as the rotor doesnt contact the caliper, the pads should be self centering. - Greg - Quote Link to comment Share on other sites More sharing options...
getZ Posted October 11, 2007 Author Share Posted October 11, 2007 They will self center, but it my experience with just about anything mechanical, the less you make it work, the longer it will last and the better it will work. I'm very meticulous (or anal) about details. Like BuZy said earlier, probably not really necessary unless you are racing seriously. Quote Link to comment Share on other sites More sharing options...
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