Need a replacement front rotor, 1976 C

Norton7d

Norton7d

XS650 Junkie
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If I run the pad shims, I notice the wavy-ness of my rotor, no shims is better but then I can hear my outside pad moving forward and back in the caliper which makes a clicking noise, so much so the clicking is bothersome at any speed.
So its likely time for a new rotor but everything new and not fancy is for 77 and newer?
What about us old guys?

Thanks.
 
Somewhere in the manual there is a spec for allowable rotor thickness. Have you measured the thickness of your rotor? I ask because I think your problem might be elsewhere? I think that I'd try a different pad first.
 
The rotor is +/-7MM, I assumed it has some warp to it considerimg orignal and never turned.
Less 150 miles on pads.
The outer brake pad has aarea to move, as the pad arm that you hold when installing the pad does not completely fill up its space and when the wheel rolls, because of the slight rotor warp, the outer pad and possibly the inner as well go from tight to tighter and during this process, the arm on the outer pad strikes the the caliper making a clickimg noise.
The noise stops when brake is applied.
If i go with a straight rotor, i can run the shims which take up more space around the brake pad arm thus reducing its movement.
Or that's what I'm thinking.


Thanks
 
To answer your original question, as far as I know, you're stuck with buying a used rotor. There's a good chance I have one.
It does sound like your rotor might be warped. I once had a warped rotor, and it was impossible to come to a smooth stop because the pads would grab and release the rotor with each revolution of the wheel. It was a pulsing sensation.
I'd put the wheel on a truing stand to verify that the rotor is warped.
 
10 thousandths of an inch? That's about as straight as your gonna get. Surely not enough to make a pad click.
Maybe someone else smarter than me will have a better answer.
 
Well it was enough that when the shims were in, the handle pulsuated notably when applied, removed the shims, pulsating went away but the clicking started.
I assumed removing the shims allowed for greater space to be created between pad and rotor thus the pad is more free to move within the caliper therefore I thought the cure would be; new straight rotor and reinstall shims.
 
I don't think I'm smarter than you DB. In my books the spec for run out is a max of .006 inches .010 is 10 thousandths. If you do have 10 thousandths of run out it is out of spec. So your problem may be the rotor.
They can be found. Before you buy ask the seller can verify the run out.
If DB has any, perhaps he can check the run out. It's not hard, you don't even need a trueing stand. The fork on the bike work fine.
Buy or borrow a dial indicator. You can piece together a mount out of scrap bits of steel to hold the indicator on the rotor off a fender or caliper mount hole.
With the wheel mounted on the bike, position the indicator to touch the rotor and deflect the needle a bit. Then zero the indicator and spin the wheel slowly while watching the indicator needle.
Leo
 
Why not just true up the rotor you have???

Any machine shop can do it.

also - I’d go and double check that +/-7mm spec. - rotor is probably like 10mm thick

maybe .7mm??
 
I may true up mine but i thought if someone sells a drilled new rotor for what I will pay to true and drill plus some more, why not go new?
 
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Thanks Gary, so other than spacers, all else is applicable, bolts right up?
Aren't modern rotors thinner, if so, does that impact braking or does the caliper adjust accordingly?
Ive seen many threads on spacers, many with you leading the way.
So what / where do I find the magic spacer?

Thanks.
 
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Stock 650 rotors are 7mm thick. You can find 5mm replacements for the later rotors from other Yamaha models (SR500, some XS1100) that will swap right on. The caliper self centers and compensates for the disc thickness. I have an SR500 rotor on my '78. Honestly, I don't notice much, if any, difference in handling or braking. I do think the 5mm rotor heats up faster and more due to it's less mass, but it's never gotten to the point where the braking suffered.
 
Yes centers and bolt alignment is the same. Pretty simple lathe project or there is (was) an ebayer would make them to custom thickness. I haven't set up an early caliper/fork with one of these rotors so don't know how thick the spacer needs to be. ( I usually use used rotors from YZF600s) Since the pistons will extend rather far when the pads wear out you might want to replace pads when they are 1/2 gone.
 
Ok, thanks, is it fair to say that a used unit might also need turning thus if already below 4MM thick, not much more meat to shave off?
Being in CA, I might have a tough time finding a facility to turn as everybody is lawsuit happy in this state.
Might just end up having a used XS rotor turned and drilled....no spacer dilema needed at this point in the game.
Thanks everybody.
 
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On the old and new style discs I compared, I only found about 5mm of difference in the offset .....

full


full


Since the discs are only 7mm thick, if the offset difference was 8mm, the older disc would sit above the newer one. As you can see in the pics, it clearly doesn't. Also, the offsets on these appear to be 19 and 24mm.
 

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