Disc Runout Limits

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TD250
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Disc Runout Limits

Post by TD250 »

I was wondering what the runout limits are for a solidly mounted disc with Brembo 08 calipers?

I currently have measured near the outside edge of the disc of 0.08 mm (0.0031") runout.
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BevHevSteve
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Post by BevHevSteve »

I don;t know what the limits are, but can you feel a pulse when you apply the brakes? If yes then do something about them. If no then don;t worry about it. That is a pretty small amount you have.........
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FabDuc
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Disc Runout Limits

Post by FabDuc »

Hi there,

I THOUGHT that I once saw that something's printed in that thin side of the disc! Just checked this, but could't find it anymore!
(May'be 'cause of corrosion!)
Take a close look there, with good light.

Regards,

Ernst
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DaveG
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Pulsing brakes

Post by DaveG »

Hi, I read the above thread, and I have a strong pulsing in my brakes - 1979 900SS with cast iron disks. Do these things warp, or does this mean I need to get new disks - could I get them reground flat?

Thanks,
DaveG
bobnorton
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Post by bobnorton »

Pulsing is often caused by a patch of corrosion where a damp pad has sat, the worst thing is to leave the bike laid up after road salt contamination. With a good long run and heavy use it usually fades out.Badly corroded discs cause heat fade and loss of all braking if decending mountains ,especially with old fluid,( the corroded disc does not take the heat away from the pad). I learnt this the hard way---twice!!.
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Post by DaveG »

Thanks for the reply, however the bike has had a run across France from the UK, and I have just changed the fluid and checked all the pistons to ensure free movement, and it pulses badly.

Could the disk have warped?
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Post by BevHevSteve »

easy enough to see if the disk has warped, just left the front and give the wheel a spin. Hold a pencil against the fork with the point at the disk...
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DaveG
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Post by DaveG »

Yes that was the first thing I did - I reckon (just holding a screwdriver up against the disk) that there is about 0.25 mms run out. And then I started thinking that this shouldn't make it pulse anyway, as the pistons should move to compensate for any slight warp.

Is 0.25mms too much? Can I get the disk turned flat or is that not practical?

Thanks,

DaveG
wdietz186
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Post by wdietz186 »

If you can find a machine shop that can grind the disc to true it you will probably have enough meat to do it. Using a lathe would be a second choice but it can be difficult because of vibration/chattering giving a poor surface.The info stamped on the edge of the rotor is the mininum thickness spec. Being slightly under that spec. would probably be ok unless you use the brakes really hard alot.When you remount the rotors make sure the mounting flange areas are clean and smooth along with torqueing the bolts evenly.
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Post by DaveG »

Thanks for the replies, I will firstly remove the disk, and use a flat marble to check the disk, and then get it ground.

I will let you know how I get on.

DaveG
Den
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Post by Den »

DaveG
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Post by DaveG »

Sorry to come back to this again, but I removed the disks, and they are definately warped i.e. bent on both sides (inside and out), so I don't see how I can get them ground down, I think I need to replace them.

Looking around the web, there seems to be an EBC replacement disk setup, and I see them for sale on the BH web shop. I have spoked rims, and the disks, really make up the hub, and also provide the speedo fixing point - does the right hand EBC disk allow the speedo to fit, or is some modification required?

Thanks,

DaveG
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Post by BevHevSteve »

Dave - the EBC disks fit straight on - no problems.
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DaveG
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Post by DaveG »

Hi Steve,
So the bit that I have drawn an arrow to comes off seperate from the disk?

http://proclassicracinginfrance.blogspo ... cture.html

Thanks,
Dave
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Post by BevHevSteve »

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You are pointing to the bearing holder, that is not part of the brake. It is part of the hub.

I would put money on your calipers and/or master cylinder needing rebuild for being the reason WHY you have overheated your disks and warped them
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