warped rear disc

[02GF74]

what can cause a brake disc to warp?

Can the disc runout be measured whilst still fitted on the bike?

i.e. is it posibble for something else to be out of true to make it apear the disc is warped e.g. hub ...

[Pigford]

Not uncommon for discs to warp...... even tho' they are quite thick
Never heard of the hub out of square.... but not a bad idea to check it whilst in-situ
You could probably get it skimmed

[tlc]

I had a problem with a pair of discs and got the disc and hub checked for runout.

Both were fine but the pulsing at the lever continued.

I wanted to get the discs skimmed but was told that stainless discs just "ring" vibrate when you try and skim them !

Apparently the only way to reface them is to flat grind them ?

I did see a place in the US that offered that service, think it was on ebay ?

Ended up with another pair of discs in the end

[Rich]

Pads binding / pistons not returning.

Yes clamp a dial gauge to the swinging arm and rotate the rear wheel to measure run out.

Personally I would buy a new one or good S/H one rather than have it skimmed.

[mikey]

But dont do what my mate done with his bmw k100 had a cracked disc took it to a main dealer as he went on holiday said "fit a new disc service it and do whatever else needs doing on it," come back from holiday to a bill of over £900!!!!

[02GF74]

Pads binding / pistons not returning.

Yes clamp a dial gauge to the swinging arm and rotate the rear wheel to measure run out.

Personally I would buy a new one or good S/H one rather than have it skimmed.

deffo not pistons. I can see the pads moving to and fro as the rear weel is turned, maybe 2 mm!! or so but was wondering if it can be something other than the disc itself.

I reckon the only sure way is to remove it from the wheel, place on a flat surface e.g. sheet of glass and then measure top surface. .... but trying to avoid taking it apart.

(I am looking for a replacement on the bay of E)

[tlc]

My local engineering shop put my wheel complete on their lathe table and then measured the face with a dial guage.

My disc was flat too.

The problem was still there and I reckon it may have been something to do with the consequences of the disc overheating !

[FER]

From a book by KEVIN CAMERON . Disc coning occurs as follows; when braking , the discs outer edge is heated more rappidly than it's inner edge , because it's velocity through the pads is higher ( the circumference of the disc at the OD is greater than at the disc ID ). The hotter , more rapidly expanding outer parts of the disc pull the cooler , less-expanded inner parts of the disc outward with them , causing the metal of the inner region to stretch permanently . Then , when the disc cools after use , this stretched inner part is to big , but the outer part is still contracting , so the disc deforms into a slight cone shape .
You can detect coning by laying a straightedge across the disc face . any coning will be obvious as the straightedge does not lie flat against the disc.

This is why new bikes have floating discs !!!!!!









fer