Bouncing Brakes??

[alga]

Actually, 10 Nm (torqued dry) is ~75% of proof load for an M6 8.8 grade bolt.
If you lubed the thread and torqued to 10 Nm, you've reached proof load, give or take.

http://www.cncexpo.com/MetricBoltTorqueNm.aspx

Useful to keep in mind when torquing various bolts with unspecified torque: ~10Nm for M6, ~25Nm for M8, ~50Nm for M10, ~90Nm for M12.

[alga]

Originally Posted by brainbug007

Is it right though that an m6 should only be tightened up to 10nm as that seemed awfully low for holding a brake disc on?

The brake disk is actually held down by the 4 or 5 wheel studs, the M6 bolts are there just to keep it in place when you take off the wheel. Sierra, for one, does not have these at all.

[ayjay]

[quote=alga;77034]The brake disk is actually held down by the 4 or 5 wheel studs,

Remember BB is referring to a motorcycle disc

[brainbug007]

Well granted the halfords one isn't the best but it was the best I could afford at the time without spending silly money and was certainly better than the clarke ones from what people said.

Daft question probly but do bike brake discs have some sort of standarized numbering system similar to sprockets? I'm wondering basically if the same disc is used on other bikes in which case I could find the same disc in better quality for a different bike that's more well known for "performance" aftermarket parts?

[ozzy1]

Only the box it comes in usually has a part number on which you can cross reference to others.Manufacturers usually use the disks on a few of their models to save on costs.Link here for Demon tweeks maybe worth a look for a new disk.

http://www.demon-tweeks.co.uk/motorcycle/brake-discs

[flyerncle]

I should have mentioned I am a mechanic and have 40 odd years worth of tools so bought decent stuff and still have it and one wrench was silly money so its accurate.

There are different torque values for dry and lubed bolts and i have seen them come loose with disaterous results and Albert has pointed that out,Not the comming loose bit.

[brainbug007]

Good to know guys. This is probly a bad idea but.. while digging around to try and find a better quality version of my disc, i came across ecb's site and started digging around there. They had an article about fitting new discs and checking the runout. they basically said that if after trying the disc in all the various mounting bolt positions you still have runout to just adjust using washers as spacers? Do you think I could get away with this and not bother buying a new disc?

[robo]

The disc mounting face and register along with the wheel bearing holes are all machined at the same time so unless the hub is damaged or the disc mounting face has some crap on it it should run true. If the discs are new and a decent quality there should be no issues. It might be an idea to clock the hub for run out before you go much further, it might also be worth looking at the hub where the bolt holes are and see if they are pulled/raised through over tightening. That may be holding the disc off the flat register. If the hubs run true bolt the discs on and clock them that will eliminate all the guess work and save a shit load of time . All quick and easy stuff, worth checking.

bob

[flyerncle]

Nail on the head Bob,putting washer's or shims under the disc will make it worse, EBC are usually pretty good and have used them on MX and road bikes.

May solve your problem if you find complete wheel and replace it.

[robo]

Originally Posted by brainbug007

Good to know guys. This is probly a bad idea but.. while digging around to try and find a better quality version of my disc, i came across ecb's site and started digging around there. They had an article about fitting new discs and checking the runout. they basically said that if after trying the disc in all the various mounting bolt positions you still have runout to just adjust using washers as spacers? Do you think I could get away with this and not bother buying a new disc?

I think you will find is they are refering to the caliper centralising, no way would they ask someone to put washers under a disc,

bob