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Old 04-20-2019, 09:34 PM   #21
JAWS
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Default Re: What could be cause these grooves on a break disc

Joe is on it.

Pressure increases as the water/fluid changes state... Ie, more pressure on the pads increasing brake drag. The ability for the rotors to shed heat is diminished and brake fade is the result.

Brakes are only as good as their ability to absorb and release heat caused by friction.
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Old 04-21-2019, 08:41 AM   #22
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Default Re: What could be cause these grooves on a break disc

just to save any confusion I don't get how you tighten down the rotor as there is barely any hex head proud of the rotor and even so, as the head is below the surface of the rotor there must be a rduced diameter shoulder that the retaining bolt(s) pull up against
I guess what i'm getting at is that this is not sup[posed to be a floating disc and the caliper/ pad is pulling up against a cockeyed disc and getting overheated?


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Old 04-24-2019, 09:59 PM   #23
Larry Ritchey
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Default Re: What could be cause these grooves on a break disc

take your rotor to a machine shop and have all the holes counter sunk. I just bet they have sharp edges on the holes. These are production disc. Takes to long to take the edges off the holes.
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Old 04-24-2019, 11:47 PM   #24
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Default Re: What could be cause these grooves on a break disc

!!! Sounds to me like Larry has hit a probable Bingo.

Prob'ly no one wants to hear any more about my grooved BMW discs; sorry*. But neither were any of them OEM products. Most were, er um, EBCs I think, and some were unidentified "good used" eBay purchases. I never thought to look for sharp edges ... because I didn't regard the grooves as a problem ... because the discs worked fine and enjoyed long lifetimes. So from my perspective, JP, your rotor has a problem only if you think it has a problem.

* Insincere.
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Old 04-25-2019, 03:54 AM   #25
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Default Re: What could be cause these grooves on a break disc

Quote:
Originally Posted by Ratso View Post
!!! Sounds to me like Larry has hit a probable Bingo.

Prob'ly no one wants to hear any more about my grooved BMW discs; sorry*. But neither were any of them OEM products. Most were, er um, EBCs I think, and some were unidentified "good used" eBay purchases. I never thought to look for sharp edges ... because I didn't regard the grooves as a problem ... because the discs worked fine and enjoyed long lifetimes. So from my perspective, JP, your rotor has a problem only if you think it has a problem.

* Insincere.
Ah! that is a very valid point.
It brakes fine now, just like the old one did.

My concern about these patterns is that eventually it will wear down the disc with those grooves, just like the other one ended up..
but I'll do both things here.

first, leading edge on the pads, second countersink the holes.

see how that goes.
Once I get that done, I'll report back and update this.
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Old 04-25-2019, 10:42 AM   #26
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Default Re: What could be cause these grooves on a break disc

When I've seen brakes dragging, it's often an old flexable brake line.
The hose closes up, and will pass fluild to the caliper and hold it.
The other thing to look at is a tiny hole in the master cyl bore. There are two;
one may be 1/8", the other about the size of a sewing needle,
which is what I use to clear it.
Make sure that the piston in the master cyl returns all the way (first)

Probably some of this has been covered- I beg your pardon if so.

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Old 04-25-2019, 12:27 PM   #27
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Default Re: What could be cause these grooves on a break disc

yes, brake hose is braided line not rubber and the hole is clear, pads are returning back
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Old 04-25-2019, 02:12 PM   #28
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Default Re: What could be cause these grooves on a break disc

I had a similar thing on a bike years ago. All was fine for a short ride but on a longer run the pads would be forced onto the disc, so much so that the disc went blue. In this case I found that the fluid return bore, a pin hole like on a fuel jet, was blocked. Once I unblocked this the caliper was fine.
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Old 04-25-2019, 03:27 PM   #29
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Default Re: What could be cause these grooves on a break disc

I guess I always thought of rotors as "consumables," like chains or sparkplugs. Maybe I replaced mine with more than the usual frequency (didn't seem like it, tho), but then as the BMs were my sole transportation I put an awful lot of miles on them, and I do ride pretty ... enthusiastically.

Rotors don't cost a painful sum + easily replaced. I'll shut up now.
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Old 04-30-2019, 01:30 PM   #30
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Default Re: What could be cause these grooves on a break disc

The second rotor seems to be the same brand as the first. Could you be cheaping out on rotors? Fab Kevin did a tech piece in "The Horse" sometime back about drilling your own rotors, and one of the points he made was that the areas swept by the holes should overlap each other slightly, specifically to avoid the problem you're having. You might consider another brand of rotor, or you could drill the holes on your current rotor a little larger. Another thing Kevin mentioned was that manufactured rotors don't need to be countersunk because they're Blanchard ground after the holes are punched, but if you're drilling your own you do need to countersink just slightly to get rid of burrs. He also said it's absolutely best to do it in a drill press.
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Old 04-30-2019, 04:50 PM   #31
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Default Re: What could be cause these grooves on a break disc

the rotor wasn't cheap, 50... or is that cheap? saying that I don't have a clue how much is a cheap or an expensive rotor.
this one came out of a proper bike shop, but not sure on make. Was a friends shop where he builds bikes (all harleys) and he had it already out, I guess because he buys in lots of them.
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Old 04-30-2019, 05:03 PM   #32
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Default Re: What could be cause these grooves on a break disc

By my lights, fifty quid is very cheap. EBC rotors (once again, tiresomely, for my old BMWs) run about $180; Galfers, about $150+. At the exchange rate of the moment, your rotor ran you about $80.

But honest: Can anybody imagine these grooves leading to a catastrophic failure? Not I. Keep an eye on minimum width, replace right away if ever you see them little cracks propagating from the drillings, and be dumb and happy like me.
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Old 04-30-2019, 05:24 PM   #33
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Default Re: What could be cause these grooves on a break disc

I agree, I dont think they will lead to catastrophic failure.

the old one was exactly the same and ran for like 6 years and maybe 20k miles. Bear in mind that I only have rear brake, that's all I use.

My question here was more out of curiosity why it was creating exactly the same pattern.

I will eventually do a leading edge on the brake pad because they definitely don't have one. see if that makes any difference, because I did like the theory that it might be digging in when the hole is going past.
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Old 05-02-2019, 07:03 PM   #34
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Default Re: What could be cause these grooves on a break disc

Think cheese grater...
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Old 05-03-2019, 10:37 AM   #35
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Default Re: What could be cause these grooves on a break disc

Never answered your original post. Grooves are from less metal at holes vs were there are no holes. As M.O.Ther said a poor designed pattern of holes with no overlap in the sweep.
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Old 05-17-2019, 05:07 PM   #36
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Default Re: What could be cause these grooves on a break disc

My opinion- forget about the pattern, the wear you show is premature, and it's because your caliper is dragging, even if it doesn't heat up enough to lock up again.

Even if you "flushed" the fluid, I'd be some of the rubber parts in the caliper and/or master cylinder are swollen or something's gummed up from the the DOT 5. If it were me, I'd order a rebuild kit for the master cylinder and new caliper piston seals, then blow every thing apart one day. And by doing this, you know you got ALL of the old brake fluid out as well.
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