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PostPosted: Tue May 10, 2016 10:34 pm 
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Joined: Sun Mar 23, 2014 9:21 pm
Posts: 535
Location: Parksville, BC, Canada
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Hi Folks;

As some of you know, I recently acquired a 2006 CBR 600 RR with 40k on it (about 25,000 miles).

The bike is straight and pretty clean but it needed maintenance. It looked like the previous owner(s) were faithful with the oil & tires - but probably not much more. The front brakes were low as well as the rear. So I ordered up OEM front & rear pads along with seals, with the idea that I would strip the calipers down and put them and the pistons through my ultrasonic cleaner and get everything back to new. I wanted lethal brakes with a nice hard lever!

After all that work, once the job was done I found that the lever was not very firm :sad: To that end I bled and re-bled the system with no significant improvement in the lever. I then checked on the 'net & found that this is very common.

One thing that people kept repeating over & over is that the bleeder screw would leak on the threads and, because of this, the brakes would suck air back into the system. I chased this theory for some time before I realized this was not correct. Let's start with some diagnostic basics first;

Q: My lever feels soft - I think I have air in my master cylinder
A: This is easy to determine. Get a pair of vise-grips and a rag. Put the rag between the jaws and adjust them so that you can pinch off the brake line going to the master cylinder with the brake lever in it's normal (not on) position. Make sure it's on the rubber line - not the braided ones down by the calipers. The rag is there so that you don't damage the rubber brake line. Don't crimp the living crap out of the line either. You just want to block it off.

With the rubber line blocked off try the brake lever. If it's rock-hard then you know, for a fact, that there is no air in the master cylinder. (what you've done by pinching off the rubber brake line is isolate the rest of the system).

If the lever is not rock-hard, then you do have air in the master cylinder or you have not fully pinched off the brake line. If you're sure it's pinched off, bleed the master cylinder. You can do that by pumping up the lever (with the vice grips still in place) and then, while holding the lever, crack the banjo bolt at the master cylinder. Be sure to have a rag under it so that the brake fluid that leaks out doesn't go all over the place. Once you have all the air out the lever will be rock-hard and you will not be able to pull it in no matter how strong you are. You will know when it's air-free because it will NOT move. You will want to make sure that the master is full of fluid before, and after, doing this.

*This is how you isolate sections of the brake system to see where the trouble lies. It works on anything that has rubber brake lines (cars, trucks, quads etc). Vice Grips with a rag between them and then block off the line(s).

OK, so now you should have a rock-hard brake lever with the master cylinder isolated by the vice grips. You can now remove them with the knowledge that you do not have air in the master cylinder and that the air must be below where the vice-grips were installed. This means the problem is lower down and that means....

Q: How should I bleed the calipers?
A: I recommend gravity bleeding them. Don't bother with pumping up the lever, flush all the old fluid out by gravity bleeding. Unless you have a buddy standing by. If you do, get him to sit on the bike with it fully upright (not on the side stand - vertical) and the steering in the straight ahead position. Get him to pump up the lever, hold it, and you crack the bleeders (gently and slowly) so that you can see the air coming out. You will see it if you crack it slightly. Tighten the bleeder while he's holding down the lever and then, once the bleeder is tight, get him to pump it up again with a few pulls, hold it, crack the bleeder and repeat until you see no air. Then repeat the same for the other side. At that point, there's no air in the system unless you ran the master dry...but back to gravity bleed/flushing.....

Just crack both bleeders, keep your eye on the level in the master cylinder and let the fluid drip out. Don't let the master run dry or you will re-introduce air into the system and have to bleed the master. Keep the master up with fresh DOT 4 brake fluid. Do this outside with a garden hose ready so that you can wash off all the fluid that will by puddling on your rims/rotors.

Special Paint Notes:

If you have Chinese fairings (especially flat black or matt black) then you should be aware that the paint probably has zero brake fluid tolerance. This means the paint will lift as soon as the fluid hits it (the paint is that cheap). My guess is that flat black is the worst because it has no clear coat on it. Normally getting brake fluid on quality paint (like factory paint) is no issue unless you leave it for hours. Quality paint will resist brake fluid until the job is done and you hose it off with water. This is NOT the case with my Chinese flat black paint. I also found that brake clean results in the same - the flat black non clear-coated Chinese paint could not withstand it at all. I bet if you sneezed on it the flat black would start to lift. Certainly, gasoline around the tank will cause stains in the flat black paint as will certain hard bugs hitting the front cowl. As will certain cloths when washing the bike. Flat black sucks! Fair warning & back to the job at hand....


Getting every last bit of air out of the right caliper is easy because, if the bike is on the side-stand, and the wheel is turned to the left, then it's already tilted so that the bleeder screw on the right side is the highest point on the caliper. That's where the air will naturally rise up to all on it's own. It won't be trapped anywhere - it wants to exit out the bleeder - so it will look after itself. Just open the bleeder and let it flow until you see no air or until you feel you've got nothing there but brand new virgin DOT 4 from a freshly sealed container.

The left caliper's bleeder (while the bike is on the stand) is not at the highest point because the bike it tilted to the left, which means that in theory there could still be some air trapped in there. We're here to nail this down once and for all...so, without spilling the brake fluid in the master all over your bike (put the lid on it), tilt the bike a little to the right. This will make the bleeder the highest point and the air will leave on it's own like it did on the right side. You can then put the bike back on the side-stand.

Once you've filled the master a couple of times you can be sure there's no air in there at all and that you have only fresh & clean DOT 4 in the entire system. You now KNOW there's no air anywhere. Period. At that point, close off both bleeders, top up the master cylinder to the fill line that's etched on the inside of the reservoir and then install the lid and the two screws.

Hose off your bike, hose off your brakes - be thorough. Wash off all the brake fluid that went all over the calipers, rim, rotor, fender, etc until it's been diluted down to nothing. Don't worry if it leaves 'streaks' on your tires, this can be removed when washing/will wear off.

Q: I did all that and my brake pedal still feels soft. It's better, but it's not rock-hard.
A: This will be the case if you overhaul your calipers (assuming you did the job right and don't have any seal leaks) and/or if you are using pads with shims on the backsides.

Q: How can that be?
A: With respect to the calipers, it's this simple, the pistons are all free now. A hard lever comes from (typically) pistons that are extended due to pad wear and that don't retract (much) when the brake is off. Typically, with mileage high enough to warrant new pads, the pistons are usually sticky and extended right up to the point where they are almost dragging. This results in a high and hard lever.

The further away from the pads the pistons are, such as when the calipers have been re-built, and the pistons are free to move back & forth, the softer the lever will be and the longer it will take for the brakes to 'activate'. Don't believe me? Take a flash light and shine it down onto the pistons on both sides of the pads on both calipers with the brake lever off. Chances are you're going to see an air gap between one or both of the pads and the piston. That air gap will lead to slower initial brake application and a lower lever. This is why people are reporting that it takes TWO pulls on the lever to get firm brake action on new pads and re-built calipers. The first pull extends the piston (brings it right up to the pad) and the second pull is the pull without that air gap which means the lever is firmer and further out. This effect is multiplied by the number of pistons in the calipers. In the case of the CBR 600 RR we have no less then 8 (!!) pistons all told....4 in each caliper.

There is a second contributing factor here with respect to a 'spongy' lever. If you used pads with shims on the back this will also make the lever spongier. How can that be? Under the OE shims is a white foam coating. Between the shims and the coating this leads to compression when you hit the brakes which is much the same as the air gap between the pistons and the pads. It adds to the delay in braking and increases the lever travel before braking occurs. Both the stainless steel shim and the white coating under it will compress.

Attachment:
Brakes ETC 074.jpg
Brakes ETC 074.jpg [ 84.21 KiB | Viewed 5666 times ]


There is a third contributing factor here with respect to the 'spongy' lever and it is rotor wear. If you look at the rotors they will likely have varying degrees of grooves in them. This means the rotor is not a perfectly flat surface, but your pads are. So there are high and low points on the rotor. So when your perfectly flat pads grip the rotor they are not gripping the entire surface of the rotor - they are only gripping the high spots. Let's say, for arguments sake, that 45% of the pad's surface is gripping the rotor, and I suspect it's less then that. This will result in much poorer brake performance then if the entire surface of the pad was grabbing the rotor. What that means is that your brakes have to 'bed in' before you will see proper performance. Once the pads 'bed in' then they will grip with 100% of the pad's surface and your brake performance will increase dramatically until you fly off the front of the bike!

So what's really happening here is that....there is a 'stackup of tolerances'

1) you have a small air gap between the piston and the pads due to the nice & fresh caliper overhaul. The pistons can retract further then they normally would when they have some miles on them causing a gap. That gap has to be taken up when you hit the brakes and this translates into a lower lever.

2) when the pistons do begin to push on the pads they now need to compress the stainless steel shim (and it does compress) as well as the white foam underlay under the stainless steel shim. This translates into a lower lever and one that does not feel as hard ('spongy') making you think you have air in the system.

3) the pads, being forced onto the rotor, are not completely making contact with the entire surface of the pad. The pad is riding on the high spots. This translates into poorer braking performance making you once more think that you have air in the system.

So there are 3 things happening here when you nail the front brakes (after a quality brake job using quality OE parts). The air gap between the piston(s) needs to be taken up before the pads start to apply, the stainless shim needs to compress, and the white marsh mellow backing under the stainless shim needs to compress as well. All of that leads to a 'spongy' lever with new quality pads. Couple that with rotors that are not perfectly flat (grooves) and then you're not going to see the brake performance that you were expecting.

This is what's leading most people to conclude there is air in the lines. They feel the 'spongy' lever, they realize that second brake application is firmer, and they, understandably, think there is air in the system. There probably isn't. It's just a function of having new calipers and new pads...

Q: This sucks! I didn't spend all that money & time just to get a 'spongy' lever! Take me back in time so that I can enjoy the firm lever I had before I did the brakes! I don't want to be stuck with this!
A: I feel for you. I went through the same. The good news is that you don't have to. This is temporary. The lever will firm up. Once the brakes bed in to the new rotors, brake performance will increase dramatically. And it does not take long. Use that front brake but also use the rear until the fronts come into vogue again.

Q:Are the OE Honda Pads worth the Extra Expense - Especially when they have Stainless Steel Shims and the compressible backing?
A:You better believe it - they are unreal pads. It's amazing how much metal they have in them. Run your fingers over them and you'll see that they are very much like sand paper. When you have a high metal content like that mating to a steel rotor - they're going to stop - fast. All reviews that I've read on my 2006 CBR 600 RR laud the brakes as unbelievably good. In fact, no-one typically tries to improve on them at all. They are THAT good. I was just speaking to someone about the brakes and I mentioned to him how fast the ridges were coming off my rotors with the new pads. You can see it very clearly. It's very much as if the pads are a brake lathe and they are machining the rotors flat.


Synopsis

By now you should be realizing that it's normal to have a soft lever when you do the calipers. This is caused by the pistons being free. If you used the high-quality OE pads then you will also realize that the stainless steel shim needs to compress along with the white backing before the brakes apply. When they do apply, the ridges on the rotors will prevent proper braking until they are 'bedded in'. So there's a lot going on behind the scenes that all contributes to a low/spongy lever.

The good news is that this is all temporary. Here's what's going to happen. One, as the front brakes are repeatedly used the pistons will eventually 'dent' the stainless steal backing. That's not really the correct term but what I'm getting at is that after some applications the stainless steel shim will be compressed on a permanent basis. It will take on a 'set'. That takes care of one issue. The same thing will happen to the 'marsh mellow' backing under the shim. That will result in increased lever height. That takes care of another issue. The other thing that will happen is that the pistons will also, eventually, stay out further (they will not be prone to retracting). This will also result in faster braking application. That takes care of another issue. The last thing, and possibly the most important, is that the pads will 'bed in', or, in the case of my bike, the pads will straighten out that rotor! I'm watching it happen after every ride. With the high metal content in the CBR 600 RR's brake pads it is very much as if the pads are a brake lathe and they are machining the grooves from the rotors.

In short, ride the bike with the understanding that you have decreased brake performance on a temporary basis. DO NOT go flying down the road at 100,000 miles and hour so that you can test out your new brakes. Drive it like it's raining. Bed those brakes in slowly but surely always allowing the rotors time to cool down before hard braking. Go down a straight stretch with no cars behind you, get it up to highway speed, and hit them fairly hard until you slow down to 20 or so. Then give the rotors time to cool off and repeat. With each application, if you are discerning enough, you will begin to notice an improvement in braking. Also, keep your eye on your rotors. I know you probably don't believe me that the CBR 600 RR will 'machine' the rotors so go and look at them yourself. Check out the grooves and watch 'em start to fade away. This is, of course, assuming you are using high metal content OE pads.

It is a fact that drag racing clutches are often made of steel with NO LINING. How can that be? Because they make so much torque that they need, literally, a metal to metal contact with the flywheel in order to hook up. The best brakes really are metal to metal (to a point). The CBR 600 RR is world-renown for it's brakes. It's because of the rotor size, the calipers and...the high metal content in the pads. This is why I say that it is like a brake lathe. You don't have to believe me, go and watch it for yourself.


Mythbusting the 'Leaky Bleeder Threads'

There's a ton of posts on the Internet about the CBR 600RR and the calipers having leaking bleeder screws and that the way to tell if you have this 'problem' is to look at the calipers after a ride and see if the threads for the bleeder screw are wet. This is all due to the fact that people are wondering why their new brakes are not performing like they should. So they are looking for some exotic problem because they want a high and hard lever. They think (understandably) that there's air in the system and when they see the brake fluid around the bleeder screws they think that this is where the problem is, that the brake bleeder screw is leaking and it's sucking air back into the system. As a result, there's now a plethora of people out there recommending using Teflon tape on the threads, putting pipe dope on the threads and just generally doing all sorts of weird things trying to get the bleeder screw threads to finally seal up.....

This is not the case. It's based on a faulty premise. The threads on the brake bleeder screw DO NOT SEAL THE BLEEDER. It's the CONE at the end of the bleeder (where there are no threads) that seals the bleeder. The threads are there so that you can tighten the bleeder. THE THREADS DO NOT SEAL ANYTHING. The cone at the end of the bleeder is what seals the deal. If the bleeder was leaking it would not come up through the threads - the fluid would come out the hole at the top. It HAS to. Look at the design of the bleeder. The bottom is a plug. The only way fluid can get through there is through the hole drilled in it.

Attachment:
Brakes ETC 076.jpg
Brakes ETC 076.jpg [ 101.17 KiB | Viewed 5666 times ]


So how does the leaking bleeder screw myth get propogated? It's this simple, it gets propogated because people don't understand the points above, that the brakes will not perform properly (assuming a quality repair) until they have some miles on them. Until then, the lever will not be as hard, and the brakes will not apply as fast, and they will not be as effective as they should be. We all want that high & hard lever with lethal braking ability. Don't worry! It will come. Put some miles on it (gingerly) until they are performing properly.

Specifically though, here's how you yourself can bust that myth. Bleed your brakes as outlined above, such that you KNOW there's no air in them, and then do this (because this is how people are getting fooled into thinking the threads are leaking) get a can of brake cleen, carefully (if you have Chinese fairings) spray off the entire caliper, gently spray out the hole in the bleeder screw, and then hit the entire caliper and the bleeder hole with compressed air until it's all dry. Then, nail the brake lever as hard as you can and hold it there for several minutes. If you have no leaks, the lever should not sink. If you have a leak, the lever will sink. This is how you test your brake job for safety. WIll it hold pressure? If it will, there are no leaks.

Now, go down to that perfectly clean and dry brake bleeder and take at close look at the bleeder and the threads. What do you see? That's right, nothing at all.

The reason the 'Leaky Bleeder Myth' has been propogated all over the Internet is simply because of this, they could not get a high and hard lever (or pedal) after a brake job....and....they bled the brakes again to no avail....and.....they did not clean and dry out the inside of the bleeder and the threads/caliper.

Don't believe me? Check it for yourself. When you bleed a system the bleeder is full of....brake fluid. When you tighten the bleeder you have 'closed' the system. The bleeder is now isolated from the system (it's closed). Yet, the bleeder itself still contains brake fluid. It's full of brake fluid! Not much, but it's there.

Attachment:
Brakes ETC 078.jpg
Brakes ETC 078.jpg [ 99.37 KiB | Viewed 5666 times ]


So here's what happens when you go down the road with your new brakes and test them out. You heat up your brakes. So what happens to any fluid when you heat it up? That's right, it expands. So the residual fluid that is left in the bleeder actually comes out the top. Where does it go? It trickles down the side of the bleeder and then dribbles into the threads of the bleeder screw and it sits there waiting to fool someone into thinking the 'threads' are leaking. This is why people erroneously think that the bleeder is leaking. It must be, because there is brake fluid around the threads.

In other words, they failed to clean the inside of the brake bleeder screw of all it's residual brake fluid. Had they done that, and then blown it out with compressed air, they would not see any fluid around the bleeder at all.

And that's how the myth of the leaking bleeder screw gets propogated. In the meantime, the rider is busy installing Teflon tape around the bleeder and using pipe sealing dope all in the vain effort to seal something that is already sealed....because...the brakes needed more time to 'bed in' on all the fronts listed above! :top:

_________________
Best & Thanks!
Marvin Miller
cbr125world Store

...because every day is MotoGP day when you own a CBR 125r...


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