260DET Posted October 14, 2008 Share Posted October 14, 2008 Pads could be moving around and putting side loads on the pistons under heavy braking. So make sure that the interface between the back of the pads and the pistons is low friction and that the pads are a very snug fit in the calipers. Metal shim plates between the pads and the pistons are a good thing. Quote Link to comment Share on other sites More sharing options...
mark Posted October 15, 2008 Author Share Posted October 15, 2008 The pads are moving a bit in the calipers as indicated by the pattern of the piston on the backing plate. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 After a weekend at CMP, I can safely say my brake problems are fixed. This is one of the old caliper that I took off the car that had the bores scored. Note the wear on the caliper. This was hitting the rotor. http://album.hybridz.org/data/500/medium/DSC001761.JPG A close up of the area. http://album.hybridz.org/data/500/medium/DSC001751.JPG I tried two sets of aluminum brackets, both allowed the caliper to rub the rotor. My theory was bracket flex. I had a set of brackets made from 3/8 inch steel using the old brackets as patterns. All mounting dimensions are the same as the old brackets. http://album.hybridz.org/data/500/medium/DSC00161.JPG Inspection of the calipers after a hard weekend on the track shows no signs of the caliper contacting the rotor. I beat on the car all weekend on a track that is very hard on brakes. A couple of notes. The new calipers are the same caliper that was on the car before. Willwood billet superlites. Same size pistons 1.75. The pistons in the new calipers appear to be cast and machined to size. The old calipers had stamped steel pistons. It seems either the aluimium bracket or the stamped steel pistons or a combination of the two was the problem. I will say I'm no longer a fan of aluminum brackets for brake calipers. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 20, 2008 Share Posted November 20, 2008 That's really good info. Thanks for following up. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 20, 2008 Share Posted November 20, 2008 That seems like A LOT more flex than the elastic limit of aluminum. One would think with that much deflection, there would be total failure. Very weird. I might draw up a bracket in Solidworks tomorrow and do a stress/deflection analysis on it after calculating the vectors involved. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 That seems like A LOT more flex than the elastic limit of aluminum. One would think with that much deflection, there would be total failure. Very weird. I might draw up a bracket in Solidworks tomorrow and do a stress/deflection analysis on it after calculating the vectors involved. I agree, it is alot of deflection. The caliper would need to move about 3/16 at least to do what you see in the pics. I checked and rechecked the mounting hardware and it was not loose. The longer the session went, the hotter the brakes got the worse the noise from the caliper to rotor contact got. At least it's fixed now. Quote Link to comment Share on other sites More sharing options...
jt1 Posted November 20, 2008 Share Posted November 20, 2008 Glad everything worked out. Having spent a good part of the weekend watching mark drive away from me, I can verify his car is working very well!!!. John Quote Link to comment Share on other sites More sharing options...
johnc Posted November 20, 2008 Share Posted November 20, 2008 I will say I'm no longer a fan of aluminum brackets for brake calipers. A lot depends on material choice. I would not run caliper brackets made out of 6061. I would be very comfortable running caliper brackets made out of 7075. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 A lot depends on material choice. I would not run caliper brackets made out of 6061. I would be very comfortable running caliper brackets made out of 7075. Any idea what Arizona Z's brackets are made of? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 20, 2008 Share Posted November 20, 2008 Any idea what Arizona Z's brackets are made of? He says the hats are 6061. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 20, 2008 Share Posted November 20, 2008 Any estimates on the G-force generated under max braking? I am guesstimating the forces on the brackets for a rough analysis. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 Tedder runs a data logger. Maybe he will chime in with a guestamate. Quote Link to comment Share on other sites More sharing options...
jt1 Posted November 20, 2008 Share Posted November 20, 2008 With some smoothing, 1.15 - 1.18g is the peak I've seen. Mark is running larger tires than me, so he may beat that a little. jt Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 20, 2008 Share Posted November 20, 2008 2300lb car, 1.25g braking, 80% braking up front, 24" tire, 10" diameter to the center of the pad. After some math, the force at the center of each caliper is about 2400 pounds force. 6061 Aluminum bracket. According to Solidworks, the maximum deflection is at the backside of the caliper of about 0.012". I pretty much ignored caliper flex by modeling the caliper as a solid block so that I could see bracket flex. I am going to post a screenshot of the deflection analysis. This is a rough guess. With steel, the deflection was less than half of aluminum. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 2300lb car, 1.25g braking, 80% braking up front 24" tire, 10" diameter to the center of the pad. After some math, the force at the center of each caliper is about 2400 pounds force. 6061 Aluminum bracket. According to Solidworks, the maximum deflection is at the backside of the caliper of about 0.012". I pretty much ignored caliper flex by modeling the caliper as a solid block so that I could see bracket flex. I am going to post a screenshot of the deflection analysis. This is a rough guess. With steel, the deflection was less than half of aluminum. Can you help out lay person and translate that? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 20, 2008 Share Posted November 20, 2008 It only moved less than 12 thousands of an inch in the CAD model. Not nearly enough to cause that kind of contact with the rotor. In reality, the strut tube mounts may flex, the caliper may flex and the bolts may flex. A total movement of about 30-50 thousands would be believable. Still not sure if that's enough to cause what you saw. Quote Link to comment Share on other sites More sharing options...
mark Posted November 20, 2008 Author Share Posted November 20, 2008 Thanks for the effort. I wonder what 12 thousands at the bracket would translate to at the caliper? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 20, 2008 Share Posted November 20, 2008 Most of the bracket deflection was sideways. And 12 thousands was at the point on the caliper that moved the most. It's the red parts of the image attached above. Quote Link to comment Share on other sites More sharing options...
jt1 Posted November 20, 2008 Share Posted November 20, 2008 Dave, how much offset did you use from the bracket to the rotor? Looking at mark's calipers at the track, it looked like the rear of the caliper was deflecting outwards from the strut tube, and the outer front corner of the caliper was deflecting down towards the CL of the hub and outwards away from the strut. The total deflection had to be around 0.150" at the front of the caliper for the caliper to hit the rotor like they did. John Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 21, 2008 Share Posted November 21, 2008 I didnt have much spare time at work so i quickly drew up the model with guesstimated dimensions. I would like to model this with exact dimensions but I would need to measure all the parts up. The car is sort of in storage but I might get a chance over the weekend. I think I made the center of the caliper offset from the bracket about 2". The force from the brake friction is applied in the center hole (of the fake caliper model) in an upward direction. The rotor would drag the pads upwards in the caliper so the force is applied upwards (perpendicular to a radian on the axle) in the photo above. John, it looks like the direction of deflection in my model is consistent with what you saw. Quote Link to comment Share on other sites More sharing options...
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