cat7girl Posted April 5, 2002 Share Posted April 5, 2002 Our car displays a curious brake symptom. When you are using the brakes hard ie Trackday you get a slight judder through the pedal. Nothing can be felt through the wheel and the brakes work great. Solid discs all round, wheel bearings all no play. Std rears. Alcon fronts, good feel, travel and bite. Disc run out is 0.05mm on 3 and 0.1ish mm on one of the fronts Any Ideas people? Link to comment Share on other sites More sharing options...
Harolddude Posted April 5, 2002 Share Posted April 5, 2002 Had the same problem,found the discs were rubbing on the retaining bolt on the alcon calipers when used in anger. Link to comment Share on other sites More sharing options...
cat7girl Posted April 5, 2002 Author Share Posted April 5, 2002 Could you expand a bit please? and how does this cause the pedal judder? Also what is acceptable run out? When we fitted the discs on the front they were running out about the same as they are 6months later. I just dont see how 0.1mm can cause a detectable sensation through the pedal Could it be anything to do with the Handbrake mech at the rear Open to all ideas except aliens.Spookey... Edited by - cat7girl on 5 Apr 2002 18:33:40 Link to comment Share on other sites More sharing options...
Rob Walker Posted April 5, 2002 Share Posted April 5, 2002 I had this problem and was convinced it was run out in my new ALcon vented front discs but on close examination the outer edge of the discs circumference was hitting the pad retaining clips in one high spot as the discs expanded under hard braking. Take the front wheels off and look closely at the edge of the disc for any shinney wittness marks, if you find any file down the edge of the retaining clips to give a mm of clearance. As regards runnout up to .010" max. Link to comment Share on other sites More sharing options...
cat7girl Posted April 5, 2002 Author Share Posted April 5, 2002 Well I have just checked the above and nothing is anywhere near fouling on the discs themselves and the runout is 2 thou on 3 and 4 thou on one I'm now thinking rears again as no judder is felt through the wheel and pedal travel always seems to be related to the rears from what has been written here previously, guess we will have to pull that end apart and look see...lovely I also dont fully understand how the adjusters work...anyone? Link to comment Share on other sites More sharing options...
David Hopkins Posted April 5, 2002 Share Posted April 5, 2002 The adjuster works as follows the piston has a nut inside it which locates on the threaded push rod inside the caliper body . when the running clearance exceeds the clearance between nut and thread the nut turns and effectively lengthens the pushrod , moving the piston out and taking up pad wear . The adjuster becomes load insensitive above certain line pressures to avoid overadjustment at hi line pressures . This is done by means of a clutch mechanism inside the piston . This is why when you wind the piston back in you have to exert a force on the piston otherwise the piston will just turn and the nut will not screw back down the pushrod thread . Can you feel the vibration when you apply the handbrake ( carefully ) dynamically . If you feel no vibration then it isnt the rears . There is nothing in the rear caliper that would cause the judder you describe . Most likely cause is Disc thickness variation on the front or rears . Measure the disc thickness @ 12 , 3, 6 , 9 oclock and compare . Link to comment Share on other sites More sharing options...
EFA Posted April 5, 2002 Share Posted April 5, 2002 My discs are the same thickness at any hour of the day teeth.gifteeth.gifteeth.gif Fat Arn Visit the K2 RUM siteid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Edited by - Fat arnie on 6 Apr 2002 00:12:13 Link to comment Share on other sites More sharing options...
StewartG Posted April 6, 2002 Share Posted April 6, 2002 This seems to be a not uncommon probem. Simon Lambert at Caterham prefers to think of it as a feature and it's caused in my case at least by hub run out. Try measureing the true-ness of the hub and the wheel as well as the disc and if they all run out together it's got to be the hub and not a bent wheel or disc. The answer? well it doesn't appear to be, get new hubs, as by Caterham's admission "the new ones will probably be the same" (or worse). You could try true-ing the hubs by either turning in a lathe using the bearing as the reference axis or possibly fettling by hand with sandpaper to remove the high spot on the disc carrying face. I'm experimenting with fully floating discs. Early results appear encouraging and the problem appears to be cured. It works on motorcycles! Link to comment Share on other sites More sharing options...
cat7girl Posted April 6, 2002 Author Share Posted April 6, 2002 OK people, I will micrometer the discs today and look for any thickness variation. Cant small things like this really be frustrating eh? Link to comment Share on other sites More sharing options...
mav Posted April 6, 2002 Share Posted April 6, 2002 Cat Girl, After leaving my car styanding for 2 weeks with the handbrake on, some brake judder was experienced. a couple of good pushes on the pedal later and all was fine. now leave the car with the handbrake off. this applies especially to trackdays, as the rear brakes seem to get very hot. Link to comment Share on other sites More sharing options...
Harolddude Posted April 6, 2002 Share Posted April 6, 2002 remove the central bolt which prevents pads from leaving caliper,check underside for signs of rubbing. Link to comment Share on other sites More sharing options...
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