Minimum Disc thickness

thanks, will try block sanding. have resleeved m/c, stainless pistons and s/s lines. brake has worked well untill recently

Sounds like the pad material transfer issue then . Read up on how to break in brakes, its pretty hard pulls downs to almost max grip many times just short of any lock ups. Braking scares me more than anything so force myself to do it to max short of crashing - if I can't bring myself to that point, time and again, then I know I'd better not be pressing very hard that day or discovered a fault that prevents it.

hobot said:

Here's some wisdom that could apply to our brakes.
http://www.stoptech.com/technical-suppo ... ther-myths

in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, (FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (FIGURE 4)

In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.

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I have had warped discs. Car discs are usually much thicker, and what the man says above is true in his experience, but not necessarily for motorcycle discs. Ducati belt twin discs were known to distort in use, and I had to replace a few when I had a 900SS and an ST2.

Warped motorcycle discs are best thrown away. A small amount of run-out can be tolerated but if you have a definite flutter at the brake lever, it usually means taking a crowbar to the wallet and buying a new disc. I know that Norton don't have a spec for minimum thickness. This may have been because they were nervous about committing to a figure for grinding a cast iron disc and thus reducing its thickness and compromising on safety. Maybe modern bikes can give us some guidelines, since most will issue a figure for run-out. My Suzuki 750 has a disc run-out limit of 12 thou (0.012"). The standard disc thickness (front) is stated as 5.3 - 5.7 mm and the service limit is 5 mm. If we split the difference - 5.5mm, then the disc is worn beyond service limits if it is 20 thou down on thickness.

As I mentioned in my earlier post, even new discs can be out of true.

ok Dave I have to bow to your comments that cycle rotors indeed prone to wrap and should write off if so. Worth a sanding or light milling attempt and hope that is tried so we learn something.

The reason rotors got narrower friction band was as they increased in OD for more leverage the speed/heat of inner parts became significantly less than the faster hotter more loaded outer rim area. To keep similar pad swept area they made lined up smaller pads in a row.

I have to panic brake almost routinely, common hazard is a season or more of heading out to highway on hilly secondary road no traffic, I cross to down side of a sharp rise to see two cars parked and talking to each other, or a huge hay rack being towed around a bend where its rare to encounter oncoming so generally just take the easier way through. I am very pleased with factory brake life saving once the restrictor melted out but am very scared now of 100 size tire that can match my panic grip like even the old worn 110 could. I have braked to point the factory forkes damping issues show up with tire hop which locks up on the leaks to chirp out on touch downs, YIKES. Grabby drum brake has taken me down crossing unseen sand layer so sure hope this instant case get smooth predicable pull down straight away.

I've gotten into habit of zooming pretty good into straight valleys between crests then squealing before cresting expecting the worst and pleasantly surprised when it was just wasted groin tension effort. If you ain't scaring yourself now and then braking very hard then you are not fully competent to save you or your bike. I too goof up at times not paying attention and sometimes too late to brake enough so first reflex I've developed is swerving around stuff in nick of time or pulling up short - ugh - next to the car or what not. I try not to think about not doing it in nick of time or the logical thing would be quit the dangerous expensive wasteful hobby and die w/o much to remember getting away with.

hobot said:

Worth a sanding or light milling attempt and hope that is tried so we learn something.

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Steve - I will look for anything that means I will avoid having to shell out for a new disc! This reminded me - sometimes, the disc itself may not be distorted but you will get flutter at the lever. One example I knew of was caused by corrosion on the hub surface and rust on the inside of the disc. Once both surfaces were cleaned up, it was back to normal. And one more example, where the hub itself is not running true with respect to the rim. This can give a false indication that the disc is warped.

hobot said:

The reason rotors got narrower friction band was as they increased in OD for more leverage the speed/heat of inner parts became significantly less than the faster hotter more loaded outer rim area. To keep similar pad swept area they made lined up smaller pads in a row.

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Interesting.

hobot said:

Grabby drum brake has taken me down crossing unseen sand layer so sure hope this instant case get smooth predicable pull down straight away.

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I don't like drum brakes!

I see you practice emergency braking - not a bad thing to do, so you are better prepared for when you're faced with a real situation. It is said that an experienced rider on a non-ABS equipped bike can out-perform ABS

Can a Norton really heat its brake to warp before just useless pressure d/t fluid boil or pad glazing? Witness marks on the chrome if any still left may give clue to warpage. I've read of cracked factory rotors and drilled ones but don't remember wrapped ones so far.


Hey Dave thanks for taking me on an entertaining education between home chores. I didn't intend to try stunts but panic reflexes beat our rational brain. I'm shaking my head right now knowing how weak I and bike are to really slow or stop in time. Left in shock about once a season by too close encounter. I'm only half insane in flashes and other half yogic trained so force my body to do stuff that makes it squeal against. Ha my Zen master of motorcycling teaches with a Whack by a Big Stick. Its nick name is THE Gravel.

I don't always test myself every trip out but ain't running no race that trip either but dam it any trip can have racer to stunter to superman brake events. So I've picked out a few places I must or should stop for any way and damit see how hard I can pull down when not insanely scared. A Cdo will not stoppie but to lift rear barely off surface then can swap ends, on the level, but for sure there's a down hill slope that'd stand one on its noise and beyond.

With the disc off I'd be sorely temped to have Norton N's and small holes water jet cut around it and 5 kidney bean holes in the inner rotor. Oh yeah I going back to 110 front as don't like so much 100 tire noise with so little whoa.

At this point in your investigation it probably makes good sense to check the seating surface of the hub for true; virtually all the hub/rotor pairs I have separated show some level of corrosion, some siginificant.

Bill.

thanks for all the input on this issue. in my case, it looks like i have a lot of things to check. will try the easiest first, block sanding rotor and new pads, and breaking in method as per Steve.