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Old 04-18-2019, 04:45 PM   #1
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Default What could be cause these grooves on a break disc

Hello all.. it's me again!

Seems like I'm having all the luck in world recently...
So Tuesday I rode down to my gf house... about 25 miles from me.
Recently I found the rear brake on my cone shovel was getting worse, but I rode to her house.
Through the country roads - here in the UK means sharp bends and lots of braking if you are going at speed. And I was basically pushing hard on that brake to overcome the fact it was feeling crap.

Got to her house, stopped and rear wheel was locked - couldn't even push the bike forward.
Brake fluid was boiling! Probably from too much use and pistons not going back in as it was proper caked. - had to crack the bleed nipple so I could push the bike in the garage.

Bike in her garage, she drove me home, got my truck and a bunch of tools and got to work.



Brake disc was proper fked. grooved..brake pads the same, and all caked. Brake fluid dark.





So I got cleaning it all up. took ages, but eventually, flushed all old fluid, put new DOT5 fluid, pushed pistons back in and out and tested first with a socket between them to make sure that braking it would hold it and brake released would let go of socket. All good.

Got a brand new disc and brake pads.
Fitted the whole thing.



Took it out for a 5 mile run.. perfect brakes. it stops.
However...

came back looking like this!! how?? brand new disc and pads, how am I getting the same pattern from before?? should it be evenly worn????




Rode back home, no problems with brakes. Now at home, to work on the Pan tomorrow morning and then she will get me to take me back so I can get my truck.. what a busy few days!!
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Old 04-18-2019, 06:08 PM   #2
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Default Re: What could be cause these grooves on a break disc

I’m not sure what the answer is but I think it lies with the drilled holes. I find it odd that the dishes out part is in line with the circle of holes and the raised part is between the circle of holes
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Old 04-18-2019, 06:17 PM   #3
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Default Re: What could be cause these grooves on a break disc

It looks like to me seeing these photos in better quality that it's breaking more on the drilled areas? no idea why but as KC said it's picking up there so the pad/braking is prominent and wearing in that area?!
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Old 04-18-2019, 07:18 PM   #4
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Default Re: What could be cause these grooves on a break disc

I wonder if the leading edge of the pad could be “dropping “ into the hole, and the then it digs the disc out when it comes out the other side creating the “valley” around the circumference of the disc? I’m thinking a different pad is in order?
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Old 04-18-2019, 07:47 PM   #5
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Default Re: What could be cause these grooves on a break disc

Well.. the previous pads were Lucas brand, specific for Jaybrake, GMA calipers and PM.

My caliper is a PM - performance machine.
Today I went to an old bike shop where they do all kinds of bikes, dude put my old brake pads against the catalogue drawings and off they come.... pads for a Honda Goldwing.

exactly the same shape as the other ones I had.
There's no left or right marked on the pads either, I just stuck them in.

BUt you are right, it seems to be where the holes are. I just can't think of a reason why it's doing that.... but your theory is pretty valid.
I'll have to double check alignment.. but can't really go wrong with a brake caliper, its a solid bracket, it spaces out evenly...

should have must bough a solid disc and save me the headache hahaha
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Old 04-18-2019, 08:49 PM   #6
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Default Re: What could be cause these grooves on a break disc

I’m hoping someone comes on here that KNOWS what’s going on here. I’ve actually seen this once before, probably 25 years ago. I bought a rode hard and put up wet not running non JJ compliant sport bike to flip. The po admitted second gear was jumping out but I knew this series of motor by heart and didn’t care. The rear brake disc was worn exactly like yours and if I remember right it had a PM caliper on it. But it may have had something else, but I can’t remember for sure. I was dumb enough to think it was made like that so the disc would have more surface area. Now I know better. I would suggest trying to find a pad that has a tapered or maybe chamfered would be a better description, leading edge. If I’m right and the squared leading edge is falling into the holes , maybe the chamfer would prevent it?
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Old 04-18-2019, 08:55 PM   #7
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Default Re: What could be cause these grooves on a break disc

The rotor looks near exactly like the cast-iron fronts on my several BMWs. They worked fine looking like that for many tens of thousands of miles; I changed them only when the minimum thickness dropped below 5mm or, in one case, when v. small cracks appeared (radiating from the drilled holes) on a disc I should've replaced sooner because of the minimum-safe-thickness thing.

As a reasonably safety-conscious fella I would say the rotor you're showing is good to go, probably for a good long time. Watch out for those tiny cracks, though.
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Old 04-19-2019, 12:28 AM   #8
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Default Re: What could be cause these grooves on a break disc

What fluid are you running...?
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Old 04-19-2019, 01:59 AM   #9
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The rotor looks near exactly like the cast-iron fronts on my several BMWs. They worked fine looking like that for many tens of thousands of miles; I changed them only when the minimum thickness dropped below 5mm or, in one case, when v. small cracks appeared (radiating from the drilled holes) on a disc I should've replaced sooner because of the minimum-safe-thickness thing.

As a reasonably safety-conscious fella I would say the rotor you're showing is good to go, probably for a good long time. Watch out for those tiny cracks, though.
Well.. The rotor is off a Harley. Place I got it yesterday morning was from a friends bike shop that only do custom bikes
But the pads I got off something else.

The previous disc was in there for over 8k miles... And was nowhere near being thin... It kinda just stopped working.

Quote:
Originally Posted by JAWS View Post
What fluid are you running...?
I'm running Dot5.1 now.

But before it had dot4 in there, for the last 4 years. A month or so ago, When I felt the brakes werent feeling right I bled them, and not having dot4 about I used dot 5 together with dot 4. But read it wasn't a problem to mix it.


I was told these days everything takes dot5?
Even on my Pan and Genny juice I put dot5 in it



Thanks
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Old 04-19-2019, 01:59 AM   #10
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Default Re: What could be cause these grooves on a break disc

curioser and curioser, can only think along KCgran's lines, are the pad locating pins all gnarly and corroded not allowing free movement of the pads, maybe try some copperease on the pins?.
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Old 04-19-2019, 02:08 AM   #11
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Default Re: What could be cause these grooves on a break disc

Hmmm. Is the DOT 5 silicone base?

Will your caliper release completely? Does the front brake drag at all?
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Old 04-19-2019, 02:51 AM   #12
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Default Re: What could be cause these grooves on a break disc

yes does release completely.
Before fitting it back I tried with a socket between the pistons - brake on..socket pinched, release brake, could remove socket.

I took this off the internet. I'm using DOT 5.1

Quote:
Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.
oh.. and I have no front brake, never had one. Rear is all I have.
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Old 04-19-2019, 01:39 PM   #13
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Default Re: What could be cause these grooves on a break disc

Ok. That was where I was going.

The dark fluid is still and indication of overheating.
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Old 04-19-2019, 01:52 PM   #14
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Default Re: What could be cause these grooves on a break disc

Was that before the fluid change?
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Old 04-19-2019, 02:07 PM   #15
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Originally Posted by Thunderbird View Post
curioser and curioser, can only think along KCgran's lines, are the pad locating pins all gnarly and corroded not allowing free movement of the pads, maybe try some copperease on the pins?.
All completely clean. I throughly cleaned everything and used green pad on the pins exactly for that reason to make sure the pads moved back freely on the pins.

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Was that before the fluid change?
Sorry you lost me.
What was before the fluid change?
What fluid I had in there?

Before there was Dot4.
I felt the brakes were a bit crap so I bled them a bit but only had dot5.1 in the garage so topped up with that.

And I rode it like that for a while.
This Tuesday was when fluid boiled after a hard ride and over doing the brake as I could feel the brakes were not so effective.

On Thursday I fitted all brand new disc and pads, and flushed all the old fluid thst was black. And put all dot5.1 fluid.

Is that what you asked?
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Old 04-19-2019, 07:16 PM   #16
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Default Re: What could be cause these grooves on a break disc

Dot 3 is the answer.
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Old 04-20-2019, 02:41 AM   #17
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Dot 3 is the answer.
Dot 3??
I don't think I have even seen that for sale.
And the boiling point on that is lower than dot5.1

Why is 3 the answwer?
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Old 04-20-2019, 10:08 AM   #18
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Default Re: What could be cause these grooves on a break disc

I’m thinking you need to rebuild the caliper. I know you said you put a socket in between and could pull it out with the pedal released, but have you tried to spin the wheel to see if it spins freely after compressing the break? You said you cleaned the pad pins, but the piston could be hanging in the bore keeping constant pressure on the pads if ever so slightly. It would explain the blueing of the original disc and the boiling of the fluid. Unless of course you ride with your foot on the pedal?
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Old 04-20-2019, 10:41 AM   #19
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Default Re: What could be cause these grooves on a break disc

I think the bluing on the old disc was because it was the caliper was so caked in crap that the pistons were hard to push back in, but I cleaned all that and now they move fine back and forwards.

The pads are a bit too thick I reckon and they slighly rub on the disc.

When I have time I will pull the pads out and file down a leading edge as it doesnt have one.
talking to someone today they also had the same theory that without a leading edge it could be digging where those holes are and therefore why the pattern.

I will try that first and report back once done.
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Old 04-20-2019, 07:04 PM   #20
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Default Re: What could be cause these grooves on a break disc

Quote:
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Dot 3??
I don't think I have even seen that for sale.
And the boiling point on that is lower than dot5.1

Why is 3 the answwer?

While on paper the 4 and 5.1 seem to out preform 3 that is only true before they become wet. Even on paper they say they should preform better wet, also. In my experience they do not, this also includes your experience as stated in your earlier post. Water in 3 combines with the fluid, in silicone based it does not. That means 100C boiling of the water in fluid suspension. Bye bye brakes is the result. Now if you were riding in the mountains it is worse, as the boiling point lowers with altitude. I found this out in the mountains in Colorado in 1986 While not a fun experience, I always have two brakes. You do not.
Open question is who else has boiled brake fluid and which ones did they boil?
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