Disc rotor thickness

[MrMelon]

Hey,

I had a pretty nasty scare yesterday, coming down a big straight rather quickly with a 35k corner at the end, I pulled the front brakes on pretty hard, and they seemed to work fine for the first 2 seconds or so, but after that, they hardly slowed me down at all even though the lever was pulled in hard. I ended up running into the gravel to the side of the corner, but when I looked at the front discs they looked absolutely cooked.. they had 2 big blue/purple rings right around them where the calipers had clamped on.

Anyway, The rotors are maybe 3.5-4mm thick, but don't seem to be warped at all. Is this too thin for disc rotors? If rotors go like that do they need to be replaced, or would it just be the pads that have been cooked and need to be replaced?

I took a couple of pics of the rotors, but can't get them uploaded at the moment. argh.

[Antallica]

Damn man, sorry to hear that. Glad you are ok and didn't hit anything nasty

[Andrew]

If you look on the rotors you will see a min thickness stamped. Use a micrometer to make sure that your rotors have a greater thickness than the minimum.

Alternatively you could take your bike to a mechanic that does WOF's and see if they are safe.

The rotors are something that wear over a long time. My guess is perhaps your brake hydraulicing system isn't working, eitherway get it checked out.

[MrMelon]

Cheers, I'll see if i can see anything stamped on the rotors.

The scary thing is that it was in at a shop all day friday getting the full service, and they said they checked the front brakes and they were fine...

Might take it back to them tomorrow and see what they have to say about it.

[wkid_one]

Air in lines??? Seems strange that the bike suddenly started doing this - unless the mech skimmed the disks (highly unlikely) I think the problem has little to do with the rotors...could be glazed pads?  air in lines?

[MrMelon]

I don't know if it's just started doing this, but it was the first time that I really had to nail the brakes hard, so it could've been like that all along.

I don't think it's air in the lines, it felt like the pads were getting pushed against the rotors hard, but they just weren't slowing me down :/

I'm thinking it might be glazed pads.. just gotta figure out how to take them out to check/replace them.

[wkid_one]

Bike User manual will show you.

If you don't have one - hunt it down online

[merv]

Fried discs certainly sounds like something wrong with the pads generating too much heat. Are there any pads lefts? Could have been metal on metal or close to it.

... and was that you heading south from Paremata roundabout yesterday afternoon?

[MrMelon]

I was told the pads on the front were fine on friday, but I'll get them checked again tomorrow.

Yep that would've been me heading south at Paremata yesterday.

[wkid_one]

They would have only checked the wear indicators and not pulled the pads out

[Motu]

Just sounds like classic brake fade to me,most likely you have soft pads in,great for around town,but not for a long hard stop.Could be your brake fluid has absorbed a bit too much water - the water boils,causing air bubbles,then the lever goes into the bar.Put in some better pads,flush the brake fluid and see how it goes.If you get judder the rotors will need to be skimmed or replaced - the blueing is not too much to worry about,but it's a sign the have been stressed a bit.The last of the late brakers no more Those satin boxers are no good for keeping the mess under control eh?

[wkid_one]

HERE IS A HOW TO MRMelonWhether you ride a sportbike or a modern cruiser, the elements in the braking system are pretty much the same. They all take advantage of a fluid element that is pressurized to provide the required forces (better known as hydraulics) to squeeze the brake pad material onto the rotor. As easy as this sounds, there are a few key tricks to making sure that your brakes are up to spec. First and foremost is making sure there is no air in the hydraulic system. Air is your enemy and can get you into serious trouble if the necessary precautions are not taken. The second most important aspect of your motorcycle's braking system is the amount of friction material on your brake pads. As you use your brakes, the material is slowly burned away in order to provide enough friction to stop your motorcycle. The third most important aspect is the condition of your brake fluid. Brake systems are not set-and-forget items on your bike. As the fluid gets old, it starts to degrade and absorb moisture, reducing its ability to perform its job. Replacing stock or worn brake pads is the quickest way to get increased braking power out of a tired system. Various manufacturers make all kinds of different types of replacement brake pads for today's motorcycles. Some claim to last longer, while others claim to give more feel and braking power. However, be forewarned that the manufacturer of your motorcycle put a lot of time and effort into developing your braking system, and there is no telling what a different type of pad material might do to your rotors or how well different pads will work with the overall design and setup of your bike. If you have any doubts, then stick with genuine factory parts.

EBC "Double-H" Brake Pads
EBC's Standard "Black" Kevlar Pads

I chose to forego my own advice and try a set of EBC "Double-H" Sintered Brake Pads on the front brakes, which claim to be nice on your rotors and still provide massive stopping power over the stock setup. However, on the rear brakes I choose not to upgrade to a better pad material simply due to the fact that the rear brakes are way more sensitive to locking up the the fronts, and replacing your stock rear pads with an upgraded type can provide too much initial bite and get you into some serious trouble. So, I chose to stick with EBC's "Standard Black Kevlar Pads" in the rear. Removing the calipers from the rotors is the first step in checking your brake pads. In dealing with your front disc brakes, first remove the

target=_>
Front Caliper Mounting Location

two main bolts that attach the calipers to the forks. Notice the bike I am working on has floating calipers and floating discs. The floating disc allows the inner portion of the disc mounting system to be made from a lighter, weaker material and hence decrease the rotating mass of the wheel and adding to the overall lightness of the motorcycle. The floating calipers pivot back and forth as pressure is applied to distribute the forces evenly over the two pad materials and keep the pads in full contact with the rotor during the entire braking process. Once the calipers are free you can slide them off of the brake discs and inspect the amount of pad material and look for anything out of the ordinary. If there is less than 1/8 inches of pad thickness left then they should be replaced.

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Internals of Front Caliper

Once the calipers are free from their mounting locations, it is time to disassemble them and remove the brake pads. On this particular setup there is one threaded metal pin that holds one side of the pads in place. The other side of the pad rests in the casting of the brake caliper. Removing this pin will free the pads and they should just fall right out. Notice the metal clips inside the caliper just beneath where the pads sit. These metal clips provide pressure on the pads to keep them from moving around inside the caliper. It is a good idea when you are working on your brakes to replace these clips. It would be foolish if you spent all this time and effort to have something so simple and cheap screw things up. Once the new pads have been assembled into the calipers and everything is torqued to spec, it is time to bleed the lines. In order for the hydraulic brake system to function properly the entire system must be fully pressurized without any air or moisture. If air and/or moisture are present in the system, it can cause a "soft" or "spongy" feel to the pedal when applied. Air can really mess things up, as it is compressible and can allow excessive pedal travel and loss of braking pressure. Moisture in the fluid will boil causing the same conditions and will also contribute to corrosion of internal brake components. There are several different techniques to bleeding brake lines. Some of the more popular ideas are outlined below.

The Old Fashioned Way

This method of bleeding your brake system can work if you absolutely don't want to spend any money to make things easier on yourself. The basic idea is to have two people, one puts a light amount of pressure on the brake lever to introduce pressure into the system while the other opens the bleeder screw on the caliper and closes it after a couple seconds, thus purging the system of a little bit of fluid and air. As easy as it sounds, it is very difficult and time consuming to completely flush out all of the old fluid and the air bubbles from the system without getting out of sync with your partner and sucking more air into the system.

The Easy Way

For not a lot of money one can purchase a couple simple devices that will ease the painful process of brake bleeding. The first (and cheapest) is a simple little spring operated valve mechanism that attaches to a plastic hose from the bleeder screw on your calipers. This valve acts as a one-way bleeder that lets fluid and air out and closes before outside air can be sucked back into the line.  Any brake fluid is extremely poisonous and corrosive and will suck the moisture out of your skin, so wear some rubber gloves when working with the stuff. It will also eat right through the paint on your motorcycle, so be careful and use towels around the master cylinder reservoirs. With moisture in mind, you want to minimize the amount of time that the fluid is exposed to air to prevent it from absorbing any moisture that will lead to poor brake performance. My advice is not to open the seal on the bottle until you are ready to use it and keep it closed immediately after you are done with it. Once you have sucked out all the old fluid, pour your new fluid into the master cylinder and begin to bleed the system. If you choose to use a vacuum brake bleeder as I did, keep in mind to read all of the instructions carefully. I had very little trouble using my vacuum bleeder, in fact the entire process took less than 15 minutes to finish. Life is so much easier when you have the proper tools. Keep in mind to watch the level of fluid in the master cylinder as to not let it get too low and suck air into the system. It sounds simple enough, but I have seen people have to start completely over because they were in a hurry and didn't remember to refill the reservoir. There should be a distinct difference in color between the old fluid and the new fluid. Once, you see only fresh fluid emerging from the bleeder screw the system has been completely flushed. As far as getting all of the air bubbles out, gently tap on all of the fittings in your brake lines to free all of the air bubbles that might have gotten stuck there. Then make sure that the master cylinder reservoir is topped off with enough fluid, install the caps, replace the rubber covers over the bleeder screws, and you are finished. Now, before you run out and test your brakes on the road it is a good idea to pump the brake levers to make sure that there is sufficient pressure in the system. Also, roll the motorcycle slowly and test the front and rear brakes before you hit the road. Double check to make sure that the pads are securely held in place and the calipers have been torqued correctly to there mounting locations. New pads usually require a certain amount of break-in for them to function correctly.

[Dave]

I ain't reading all that shit but here it is:
If the lever still felt o.k. but the bike wasn't slowing down-it's nothing to do with the hydraulics.
It will be crap pads.At the service all they do is check the amount of pad left-they have no way of knowing what compound pads are fitted.
Unless the lever pulses when your braking-the disc rotors will be o.k.

suggest you buy a good brand quality pad and try again.

Check with the w/shop that did your service-they might have changed your fluid anyway-Good preventative maintenance.

[MrMelon]

Cool, I'll take the pads out tonight, and if they're glazed I'll sand them down a bit, or just replace them.

Will I need to bleed the brakes after just replacing pads?

cheers

[Dave]

Brake fade-as you just experienced is often caused when the brake pad goes beyond its recommended operating temperature,when this happens the resin that glues the pad together boils and comes to the surface of the pad-making the pad loose friction and not work effectively. This is the glazing that you can see. If you are content not to brake this hard again,then de-glazing wil be fine.If you plan on braking this hard in the future then it will continue to happen until you crash! or replace the pads.
You won't need to bleed the brakes after fitting pads,but it pays to replace your fluid at least every 6 months.
Don't use racing brake fluid unless your racing-because it must be replaced after every meeting.