AC Owners Club Forum
AC Owners Club Forum => Cobra (Thames Ditton) Forum => Topic started by: rsk289 on July 23, 2019, 11:10:18
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Does anyone have a figure for the max permissible runout on a rear disc for a leafspring car? I've just rebuilt a rear hub with new RHP bearings, seals etc. and a new disc, and despite having a machine shop set the interference tolerance for the axle shaft fit, true up the hub face for the disc fit and check the run-out on the bench, I have 5 thou runout at the edge of the new disc. I had terrible brake judder before under heavy braking, and suspect I still will have (won't know until the new pads arrive). I wonder if there's a problem with the hub?
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Just to say I've sorted this and now have around 0.001" run out on the disc, and all my pedal vibrations have vanished! So have the flickering brake lights...
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For future reference what was the issue/solution?
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The issue is a little involved!
My hubs and discs are double drilled to allow for peg drive, which I don't use. When the parts were machined, the machinist couldn't get the disc-to-hub mounting bolts through the holes due, probably, to over-enthusiastic plating of the hub. Rather than re-drill the holes, he used nuts and bolts through the peg-drive holes, which are slightly larger.
The parts were indexed, but when I assembled the hubs I clearanced the bolt holes slightly and assembled correctly using those. I suspect I managed to get some debris between the two, but nothing showed on another dismantling. Another careful cleaning and assembly and it's now fine. I've done a test drive (Silverstone Historic) and all vibration under braking has gone, making it a lot more pleasant to drive.
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Thanks for reporting your solution!