Minimum Disc thickness

I am still having trouble with my front brake and have started looking at another angle. I know I have a high spot on the disc and have thought about having it ground flat again. Can someone tell me the minimum thickness allowed for the front disck. I can't seem to find that informatin in my manual.

Thanks in advance.

We've covered this this year and conclusion was you are on your own judgement to what you think ya can get away with as no data on Lockheed rotor wear minimums exist. The main deal is the thick the better able to resit heat w/o distortion so if not race heating likely a non issue if the pucks can still move enough to clamp on on it. Might also look up downside of standard spiral grinding methods.

Those 1st gen discs are typically a couple of mm thicker than modern bike discs, should not be an issue to skim a bit off, but as hobot remarked, check pad wear/piston travel.
It would be ..bad - to have one pop out - in use..

.250"

Thanks for the info. Good thought hobit, but I do not plan on using a standard spiral grinder. I am specifically going to find a GOOD machine shop with a Blanchard grinder if I go this route. I am only hesitant to buy a new one because I am not all that sure this is the problem. This is just the only thing I haven't tried on the front brake issue.

It should be relatively simple to mount a Verdict 0.001 inch clock gauge
on to the forks and spin the wheel to check if there is a high spot.

hobot said:

We've covered this this year and conclusion was you are on your own judgement to what you think ya can get away with as no data on Lockheed rotor wear minimums exist. The main deal is the thick the better able to resit heat w/o distortion so if not race heating likely a non issue if the pucks can still move enough to clamp on on it. Might also look up downside of standard spiral grinding methods.

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This brings up an interesting point... a brake works by converting kinetic energy into heat energy. Once a rotor becomes heat saturated, it becomes totally ineffective in slowing a vehicle... as in... the brakes will have no effect what-so-ever on speed reduction. The thicker a rotor, the more heat it can absorb... which becomes an issue long before worrying about warping or pucks jamming.

Main risk taking on thinning Norton's almost cast iron like rotor is cracking more than distortion. Peel's Wave rotor is .22o" thick but its a new age alloy with special tempering treatments. Machining tool line direction does make a significant effect of drag down and search up to review this. i'd not worry about .25" thick Norton rotor, especially if made holey as Hienz Kulger did or similar. Just have the mounting holes slightly ball peaned around edges but the friction area holes don't need to be and reduces the bit on pads. Less spun mass to slow down does help make the tire sing louder sooner. To break in new brake and pads one should gradually work up to As HOT as you can get it just short of any lock up which can weld or remove metal and pad material on surface. I've poked out the rubber resistion hole so only the tire lock up is an issue to stop faster, though its not two finger easy leverage tire squeal to lock up, it as good a tire stopper as anything out there, even with power brakes and ABS, if scared enough the grip force is not even noticed. I had tried to run factory brake into heat fad zone, but only times I could was really dangerous series of pull downs to get to point the tire no longer squealed, till ALL the air and moisture ahereing to surfaces cooked off then never again could induce fade I could detect. Extra rotor and extra big rotors don't really stop any faster than stock brake, just lasts longer and less able to boil fluid racing braking a LOT. Don't know about the rest of the world but I only worry about tire compound, air pressure and surface conditions to save my bacon, not brake power itself. Hope you get the pulse sensation solved and would like to hear if indeed the rotor shape was the issue or not.

really interested in this thread, as pulsing does occur time to time and don't understand the reasons why. hope you get it resolved and post it.

Its possible for some surface grime pollution to cause pulsations but most common is lumpy or distorted rotor working the pucks back and forth. At high brake loads it can also be lack of fork dampening allowing some tire hop and some can be the tire itself. Brake pulsations on loose stuff is bad juju so I've disconnected ABS on my car, on/off road 'puterized bikes have away to shut it off too. Cryogenic tempering is advertising point of many hi end rotors so might consider that cheap treatment after the rotor sliced evenly on both faces and maybe made lacy-er. Oh yeah and the pads too, and the clutch pack and now that I'm thinking of it the dang tires too, hmm, says it helps gut string guitars and women's hose. As its the uneven heat factor that distorts rotors might want to heat the rotor up while its being milled almost perfect.


http://www.cryogenicsinternational.com/rotors.htm

Robb2014 said:

This brings up an interesting point... a brake works by converting kinetic energy into heat energy. Once a rotor becomes heat saturated, it becomes totally ineffective in slowing a vehicle... as in... the brakes will have no effect what-so-ever on speed reduction. The thicker a rotor, the more heat it can absorb... which becomes an issue long before worrying about warping or pucks jamming.

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I agree.

You need to determine the run-out with a dial test indicator mounted on the forks, as Bernhard has suggested. If it is small, e.g. less than 5 thou, and if there is no wear 'lip' on the disc, then grinding might be OK. If there is a wear lip, the thickness of the part of the rotor that the pads bear on will already have been reduced from optimum and grinding will make it thinner still, and might make it even more prone to warping. What is the thickness of the worn and unworn parts of the disc? If the disc is 30-40 years old, it will have done its time and I would suggest you replace it.

P.S A friend who built a T150 recently bought two new Lockheed discs and they were both out of true. He had to take about 0.005" off each side to get them true. This is a double disc set-up that works very well now. I would regard that as a maximum. Don't forget that if you have a 'hop' even as small as 5 thou you will have to re-surface both sides, so that you could end up removing 10 thou.

I would still say that if it is an old disc with a lot of miles on it, you should replace it.

I have a 75 Commando and turned the chrome off the OE disc with a brake lathe, It works much better, wear and warping has not been an issue.

motoracer8 said:

I have a 75 Commando and turned the chrome off the OE disc with a brake lathe, It works much better, wear and warping has not been an issue.

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Might even work better if you have it ground.

not my thread, don't mean to hijack, but thanx all for the input. methinks my rotor is past its service life. chrome ground off a long time ago and re-ground once since then.obviously not flat no more. cryo didn't seem to work too well for Ted Williams, but what did he know about Nortons?

I don't know that a ground finish is any better than a lathe finish. A brake lathe cuts both sides at the same time so both sides are paralell.

motoracer8 said:

I don't know that a ground finish is any better than a lathe finish. A brake lathe cuts both sides at the same time so both sides are paralell.

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That's what I thought too until hobot posted about the difference.

stop-turning-brake-rotors-t10262.html

Apparently turning is no longer the preferred method.

Spiral turning finish lines has been found to reduce rotor pad friction.
Blanchard grinding is better way to go for cross hatched finish.
http://www.precisiongrinding.com/Grindi ... inding.htm

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.

ok hobot, what you say makes perfect sense to my senseless brain. that would explain why it seemed to just start happening out of nowhere, not after a heavy use/heat cycle. so what would be the best method of removing imbedded friction material and not comprimising rotor flatness?

Gosh after reviewing the basic scope online I'd think just hand block sanding or sand blasting would do the trick. You are the one with the best chance of telling us what worked - as you escalate up the surface attack methods. BTW if you don't have upgraded resleeved master cylinder w/o *Any Restriction 'valve*' as Lockheed does, then you may be pleased with the definite lock up ability by removing all restriction with a big fat cherry red hot nail. It don't make the brake easier to squeal but dam sure makes your hard squeeze stop the wheel, while prior I could not get tire squeal or lock up no matter my panic state or how renewed or cleaned surfaces. May have to try another rotor and new pads in the end.