Hi All, I'm presently building a 72 Commando with a standard front disc brake. I have two discs to choose from, an original that looks OK and a new disc I bought 11 years ago. I checked the original disc for true and it has .008" run-out. I thought I'd check the new disc while test equipment was rigged up and that is very similar. This test was done on a lathe against a perfectly true made for purpose disc holder (also checked the holder with dial gauge for true).
My questions are, am I just unlucky here or is this common for Commando std discs to be this inaccurate?
Will the brake work or judder when applied with .008" run-out?
Sorry if these are stupid questions in this modern age but it's been a while since I had a disc braked Norton!
Regards, Alan
Hi Alan, I bought an old d…
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Thanks Dave for your input…
Thanks Dave for your input.
After looking carefully at my original disc I realised it had a very even 'half to the left, half to the right' run-out. So I have had the 'hub face' of the disc ground flat with the disc side downwards. This has 'trued' the hub face to the discs pad faces, the pad surfaces of the disc have not been touched. Once set up in my dial gauge test, it now shows a no more than 1 thou of an inch error. I have been told a brake disc idealy should have less than 2 thou run-out. So now I think my old brake disc is usable once again.
Road test will let me know how good (or bad) it is.
Alan
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Hi Alan, I bought an old disc from Norton Motors when it was at Rugeley. Thinking, like you, they are pretty solid and unlikely to be warped, wrong. I took it to an engineering company with a surface grinder, They did the top of the top hat first, the bottom of the rim of the top hat second and finally, the top of the rim last in a series of straight sweeps. Seeing as the surface grinder can be bought down in less than 0.0001" at a time the result was spot on and took the guy less than an hour.
Dave