david nelson Posted September 30, 2004 Share Posted September 30, 2004 How do I measure the disks to see if they have warped? David Link to comment Share on other sites More sharing options...
Ferrino Posted September 30, 2004 Share Posted September 30, 2004 You could use a dial gauge mounted on a magnetic stand. Link to comment Share on other sites More sharing options...
Bare Posted September 30, 2004 Share Posted September 30, 2004 Drive the Car :-) warped Rotors are Not subtle.. gives a 'square wheel' pulsation.. unmistakeable. Link to comment Share on other sites More sharing options...
david nelson Posted September 30, 2004 Author Share Posted September 30, 2004 They are warped but I would like to know by now much as at £120 +vat each its going to cost lots to sort out. If the are slightly warped then I might be able to get the skimmed. Link to comment Share on other sites More sharing options...
Mr Locust Posted September 30, 2004 Share Posted September 30, 2004 David, Taking a break from the speed events forum eh? Assuming you don't have a dial gauge or similar.... Clip a lollipop stick or other blunt instrument (lightly) to the track control arm using mole grips or similar so that the end touches the inside of the rotor. Spin the hub and the stick will be pushed back by the high spot of the disc. If you measure at the low spot i.e. biggest gap after you have spun the disk round (most people have a dodgy set of feeler gauges in the toolbox) to get the max run out at that point. Once you get over about .003"-.004" max/min you will feel it through the pedal. Standard or AP rotors by the way? Just out of interest. Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
ruff seven Posted September 30, 2004 Share Posted September 30, 2004 You can not warp a brake disc! Link to comment Share on other sites More sharing options...
david nelson Posted September 30, 2004 Author Share Posted September 30, 2004 AP rotors. I think the near side is miles out, what I do not want to do is replace the disks and have the same thing happen again. I think it will cost about £350 for pads and disks and I do not want to throw money away. I am down at Llandow on Sunday, so if anyone that is going down could help/have a look/ bring a gauge, please could you help me out? David Link to comment Share on other sites More sharing options...
F355GTS Posted September 30, 2004 Share Posted September 30, 2004 David I had mine skimmed and a few months later the cracked ☹️ Mark Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 30, 2004 Share Posted September 30, 2004 The warping is a change in the metal crystalline structure caused by poor brake pad bedding in. Once it has started it propagates with every application of the brakes - you need to dress the disc with "garnet paper". Aluminium oxide paper *WILL MAKE IT WORSE*. Check this out Link to comment Share on other sites More sharing options...
Mr Locust Posted September 30, 2004 Share Posted September 30, 2004 David, Examine the surface. Mine had what appeared to be fine radial cracks / black lines in a number of places which also lined up with position of the vanes inside the rotor. Car was To start with, the 'pulsing' effect was only pronounced once the brakes had had a good firm stop or two on them and was then pronounced for the rest of each drive i.e. not really noticeable immediately from cold. This got progressively worse until it was there all the time. I clocked them before discussing with CC (using a dti clamped to the track rod) and there was c .006" - .008" run out. Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Ferrino Posted September 30, 2004 Share Posted September 30, 2004 David - you are welcome to borrow my analogue DTI and magnetic stand (Abingdon) if you like. Link to comment Share on other sites More sharing options...
david nelson Posted October 1, 2004 Author Share Posted October 1, 2004 Peter I did the garnet paper bit at the weekend and have tried to go through the beding in process and all seems well, but the only time i have noticed the problem has been during track days when the brakes get v.hot. I hope to get some temp into them at Llandow. Again thanks for your offer of help see you there. David Link to comment Share on other sites More sharing options...
christian.v Posted October 1, 2004 Share Posted October 1, 2004 Not much chance of getting heat into anything judging by the weather warning out this morning 😬 Link to comment Share on other sites More sharing options...
charlie_pank Posted October 1, 2004 Share Posted October 1, 2004 I had exactly the same symptoms, fixed by the ole garnet paper trick. BTW the best place I found to buy this was toy modelling shops. Link to comment Share on other sites More sharing options...
ruff seven Posted October 1, 2004 Share Posted October 1, 2004 But you still can,t warp a brake disc! see peter c,s link. Link to comment Share on other sites More sharing options...
Mr Locust Posted October 2, 2004 Share Posted October 2, 2004 Ruff, whilst the theory of non uniform transfer of friction may be a perfectly good explanation for the underlying cause of brake problems - discs do in practice distort. I have removed discs from a vehicle in the past which had c. .160" run out on a .375" thick friction surface an a uniform section thickness which was above the minimum. Dial indicators were not required in this case. IF THAT'S NOT WARPED, DISTORED AND GENERALLY KNACKERED I'LL SLEEP OUT. This was on a Citroen car where the brake pedal controls a valve on the hydraulic system rather than being direct acting - and there was no pulsing through the pedal. In the case of the Caterham/AP brake problem I experienced, fine surface breaking cracks were observed on the face of the rotor which were in line with the vanes in the vented disc and the run out had increased from .002" to .008" - which feels a lot on such a light car. Irrespective of the underlying cause of the problem, most manufacturers service information will quote new thickness, min thickness and max run out for brake rotors. There is obviously for a reason for this Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Bare Posted October 2, 2004 Share Posted October 2, 2004 Dunno about Solid Rotors but I've managed to Warp more than a Couple of Vented Rotors..on my 'regular' cars tho.. Serious Measurable Run-out..No Fiction here ..this is Real and unfortunately all too easily repeatable :-) Skimming seemingly only Patches it.. It soon returns I've found.. fresh Rotors are the only Sure remedy. although possibly a Heat treatment might do the trick, just conjecture tho.. however new Rotors are 'usually' relatively inexpensive. After Many theories from Factory Mechs.. including the "Gotta use a torque wrench on the Wheel Nuts".. good advise but not the root cause I suspect. Finally Deduced that (in My case) it' was due to heavy brake Usage.. as in a rapid stop from Hi Way Speeds.. where some clever Civil Servant had opportunely placed a Traffic light, then keeping my foot on the brake while waiting.. this caused differential cooling on the Rotor(s).. and a slight warpage..evident as soon as the v next brake.. NOT keeping the pads firmly pressed against the Heated Rotor seemingly avoids this in my experiences. This technique.. or lack of it :-), has worked for some time now.. same Family car(s) same conditions.. worth a try if this is a genuine problem for others. Link to comment Share on other sites More sharing options...
Paul Wiley Posted October 2, 2004 Share Posted October 2, 2004 Memory retention is the reason why skimming does not work and comes back when heated to more extreme tmps. Link to comment Share on other sites More sharing options...
david nelson Posted October 7, 2004 Author Share Posted October 7, 2004 Just come in from measuring my disks. Used a DTI gauge and have the following readings Nearside front outer face 0.003 Inner face 0.004 Is this bad 🤔 David Link to comment Share on other sites More sharing options...
Mr Locust Posted October 7, 2004 Share Posted October 7, 2004 I would have said that .003"-.004" is on the limit of what is permissible (much rather see .002"-.003"max) but the fact is it's obviouosly developed to a point where you have noticed it so it won't get any better. Is there any evidence of surface breaking defects (cracks or areas of porousity) which will give an intermittent grab characteristic? If you've tried the abrasive clean up trick; Looks like a straight choice of live with it (if it's not too bad), skim or replace. Personally, I don't bother skimming discs and living with defects in safety critical items is a matter of how much you value your neck.... Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
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