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Brakes - Warped Rotor Fix


HispanicSlammer

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Excellent...I think it goes to figure that the aluminum carriers are easily tweaked...putting the  steel rotor out of true...not necessarily an easy fix...but easier on the wallet to fix.

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This is interesting... I don't have any dragging brake discs, but spinning the bobbins is an interesting thought.

 

Despite the misgivings of some on here, the point of the bolt is not to "compress" the bobbin. It's just used as a way to grip the bobbin so that you can turn it and clear any trapped debris. It actually works quite well, though I'm sure EBC would just as soon sell you new rotors. If you're having to apply real force, you have a problem beyond the scope of this method.

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Yes, the reality of the "pulsing rotor" situation on a car or motorcycle can be a warped rotor, but the more common cause is an actual re-tempering (by heat) of a small (brake pad sized) area of the steel alloy of the brake disk.

When a brake disk is heated up to very near its maximum operating temperature, due to something like a situation where there was a long period of brake use on a long downhill run (this is common with inexperienced drivers who don't know how to "gear down" the transmission rather than constantly use the brakes), and at the end of this period of extreme heating if the driver/rider is faced with a reason to come to a complete stop and sit for a while (like a traffic light or a stop sign) if the driver/rider holds the brake lever/pedal down during that time the area of the brake disk that is located under/between the brake pads can undergo what is essentially a re-tempering of the area under/between the brake pads.


This re-tempering of the small area of the brake disk held under/between will result in a slight change in the crystalline structure of the steel alloy in that area.  Once the brake disc cools the change is permanent.  Forever after this event this small portion of the brake disc's surface area that got re-tempered by this extreme heating event will have a slightly different coefficient of friction from the rest of the brake disc area.

 

The permanent result of this change is that when you squeeze the brake lever (or press the brake pedal) the brake pads will experience less "bite" (a lower coefficient of drag) as they sweep over the small (brake pad size) re-tempered area of the brake disc.

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50 minutes ago, GreginDenver said:

Yes, the reality of the "pulsing rotor" situation on a car or motorcycle can be a warped rotor, but the more common cause is an actual re-tempering (by heat) of a small (brake pad sized) area of the steel alloy of the brake disk.

When a brake disk is heated up to very near its maximum operating temperature, due to something like a situation where there was a long period of brake use on a long downhill run (this is common with inexperienced drivers who don't know how to "gear down" the transmission rather than constantly use the brakes), and at the end of this period of extreme heating if the driver/rider is faced with a reason to come to a complete stop and sit for a while (like a traffic light or a stop sign) if the driver/rider holds the brake lever/pedal down during that time the area of the brake disk that is located under/between the brake pads can undergo what is essentially a re-tempering of the area under/between the brake pads.


This re-tempering of the small area of the brake disk held under/between will result in a slight change in the crystalline structure of the steel alloy in that area.  Once the brake disc cools the change is permanent.  Forever after this event this small portion of the brake disc's surface area that got re-tempered by this extreme heating event will have a slightly different coefficient of friction from the rest of the brake disc area.

 

The permanent result of this change is that when you squeeze the brake lever (or press the brake pedal) the brake pads will experience less "bite" (a lower coefficient of drag) as they sweep over the small (brake pad size) re-tempered area of the brake disc.

I belive GreginDenver is Right On. This information on automobile hard braking to a stop and remaining on that super-heated area was the subject of a local motor mouth article explaining how brake rotors get warped.

Well said Greg.

 

BTW: I've done the free-the-rotor-buttons/bobbins proceedure without any negative impact.

 

 

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Very much agreed on cars... motorcycles may be more of a mixed bag. The difference with bikes is that the discs are much thinner and far more exposed. Realistically, warped is a bit of a mis-characterization... more like tweaked, and as has been noted, it is probably the carrier that is the issue. 

 

Also, anyone who is concerned that they may have compromised the integrity of their parts: rather than X-ray as zRoYz mentioned, dye penetrant is an excellent form of non-destructive testing and can be performed at home. Completely unnecessary for brake discs unless you've really hammered your parts, but if you need something to make you feel better this would find the cracks that won't be there. Pretty useful stuff for the gear head when looking at parts of unknown history (heads, pistons, connecting rods, cranks...). The test isn't difficult (YouTube it...) and it's available at welding shops.

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Does he ever get to the point? I'm 7 minutes in and I haven't heard anything but basics yet.

 

Edit: 15 minutes and he still hasn't convinced me, or presented any information that I wasn't already familiar with. I get that the bobbins don't need to spin, but I'm not trying to make them spin, I'm trying to clean crud out of the gap. A couple of twists with a socket wrench will do it... (I'm with him that spinning them with a drill is stupid).

 

Well, it ran out in the background while I typed this and he still hasn't convinced me, but make up your own mind... I mean, he's wearing a riding jacket to make his video, so obviously he knows what he's talking about.

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  • 3 years later...
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I must have tweaked my carrier putting a tire on last year.  I keep noticing it under hard braking...so it must not be too much.  Putting the dial indicator on a stand and checking runout as I type.  I'll post some numbers shortly.

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Left rotor had about 7mils runout (0.007") and Right had about 6 mils runout.  Afterward the Left is at +/-1mil runout and the Right around max 1.5mils runout.    I'll ride this morning to check if the shudder I was experiencing braking is improved or not.  IF NOT I'll be checking he head bearings and make sure the nut is torques correctly...if the shudder is gone I'll know I most likely bunged the rotors last couple times I changed tires.

 

Matt

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Weak rotor carriers must be a 5th/6th gen thing. My 1st gen, 2nd Gen, and 4th gen never had these issues. yet my 5th gen and my 6th gen had warped rotors when I purchased them. 

No amount of Bobbin cleaning helped. I ended up replacing the rotors.

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3 hours ago, slowbird said:

Weak rotor carriers must be a 5th/6th gen thing. My 1st gen, 2nd Gen, and 4th gen never had these issues. yet my 5th gen and my 6th gen had warped rotors when I purchased them. 

No amount of Bobbin cleaning helped. I ended up replacing the rotors.

these rotors aren't "warped" so to speak...the carriers are about 4mm thick stamped aluminum...and I've seen people hit curbing with them and bend hte carriers...whether they are "fragile" or not the carriers are pretty standard for japanese bikes and most people just plop down money as they have no way/idea on how to fix the issue.  I've had these on the bike for 9 years and I got them REALLY bent second hand.  BUT they had more meat on them than the stockers which had 76k miles on them.  So, I swapped, bent and got them back into true.  I probably bent tthem trying to break the bead (I do my own tires)...when the rim slipped a little on my bead-breaker--applying about a shit-ton of my weight on a lever trying to break the bead...a not so gentle treatment of the rotor/tire carrier.  IF I look at the run-out--the data shows it to be out of plane--I'm just bring the disk all into alighment with the rotatioary plane of hte wheel.

 

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If you even just look at this style of rotors wrong, they will be out.  I true them quite often.  I buy cheap, low mileage OEM rotors for projects and inevitably have to "adjust" them when they arrive.  But you can pretty easily get them within a fraction of the quite large factory service limit.  I had a pair of BADLY bent rotors off of a crashed 97 VFR wheel that I wanted to use on a bike I was selling.  Took me a while, marking and adjusting, measuring and repeating, but I got them well within limits and you couldn't feel a thing at the lever.

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My Suzuki 750 was the same. I'm not sure I've had a bent rotor on any other bike in my life. Those ones bent all of the time. 

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On 9/27/2022 at 5:50 PM, Captain 80s said:

If you even just look at this style of rotors wrong, they will be out.  I true them quite often.  I buy cheap, low mileage OEM rotors for projects and inevitably have to "adjust" them when they arrive.  But you can pretty easily get them within a fraction of the quite large factory service limit.  I had a pair of BADLY bent rotors off of a crashed 97 VFR wheel that I wanted to use on a bike I was selling.  Took me a while, marking and adjusting, measuring and repeating, but I got them well within limits and you couldn't feel a thing at the lever.

 

I wonder what it is about these Rotors that make them bend/warp so easily while non-5th/6th gen VFR's aren't as problematic. As I said before, I never had these issues with any of my other gen bikes, and a quick google search shows bikes that use the same Rotors suffering from the same. 
 

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4th Gen and CBR600F3 discs is what I work with and they seem to be somewhat fragile too.  I think they are just vulnerable from life, like maintenance and getting bumped.  I'm just glad they are easy to "fix" but that is also why they are easy to "bend" I suppose.   The lighter but still strong enough ratio can be hard to balance.

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