Author Topic: Rear disc runout  (Read 674 times)

rsk289

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Rear disc runout
« on: July 23, 2019, 11:10:18 »
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?

rsk289

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Re: Rear disc runout
« Reply #1 on: July 25, 2019, 09:52:17 »
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...

Flyinghorse

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Re: Rear disc runout
« Reply #2 on: July 27, 2019, 11:06:24 »
For future reference what was the issue/solution?

rsk289

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Re: Rear disc runout
« Reply #3 on: August 04, 2019, 14:01:52 »
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.

bbrown

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Re: Rear disc runout
« Reply #4 on: August 05, 2019, 02:43:23 »
Thanks for reporting your solution!