#!@&% Front brake!

Back a number of months ago, I noticed my front brake getting a little spongy....on my 2004 Yz450f.

I hadn't done anything to it at all. So I decided that if I was gonna work on it, I'd put new Sintered brake pads on, convert to a "CR" style of cable routing, and use a Galfer Stainless steel brake line.

I did everything, and the brakes were about 90% free of spongines. I even let it sit overnight with a cable tie on the lever, which did help, but still there is sponginess...I basically learned to live with it, but decided today to take off the caliper, and suspend it from my Garage ceiling so that when I went to re-bleed it, it would be about 3 feet higher than the Master Cylinder.

I suspended the caliper, placed a piece of steel the same thickness as the rotor between the pads, and had the Wife work the lever while I cracked the bleeder valve. I figured "this time it's gonna be like a rock" No dice! after re-bleeding it, it still has some sponginess.

I'm at a loss!!

THe only thing I can think is that either the Master Cylinder or the caliper itself has some type of leakage, that's letting air in. How can I determine if either the Master Cyl. or the caliper needs a rebuild kit???



Don, as silly as this sounds try this. Reinstall the brakes on the bike. Take a tye wrap, piece of duct tape, or whatever. Pull the brake lever in and tape it to the grip. Leave the lever like this overnight. Its more than likley the sponginess will be gone.

I learned this watching Kyle Lewis's mechanic at a supercross years ago. He always taped his lever to the grip and I asked him why. He said it was to let the last little bit of air rise to the top...it really works.

I never cared much for my galfer pads. They did not have as much power as stock and appeared to be built to last a long time. Honda brake pads are the best. Even the stock Yamaha pads are better than Galfer.

I even let it sit overnight with a cable tie on the lever,
He did that.

The bad thing about the front brake is that the caliper is at the bottom and the master cylinder is at the very top. But the good thing is that the caliper is at the bottom and the master cylinder is at the very top. Let it sit for a while with the bars turned left so the hose is really straightend out and near vertical. After a few hours, remove the MC cover and gently squeeze the lever just far enough to move the MC piston the first 1/8" or so. Air that may have been mixed into the fluid will have risen to the top, separated itself from the fluid, and gathered just under the fill port at the bottom of the reservoir. Bumping the piston a little will push the air out the top. It's important not to push the lever too far, or too vigorously as that will push the air down the line. If you're lucky, you'll get one good bubble, and you'll be done.

Works for me.

As far as leaks, it is nearly impossible for a caliper to allow air in without leaking fluid out. That's not true of the master cylinder. If the air comes back without an external leaks, suspect the MC.

I had a mastercylinder go bad on one of my older bikes. The brakes would tend to get mushy after using them for a day or so.

The cure was to rebuild the m/c. Very easy to do. Before I rebuilt it, I did notice that it would not hold pressure for long. If you grabbed the brake lever and held it at the point that the braking got stiff, it would only last for a minute or so. Then you had to pull the lever another 1/2 inch or so. . Onward it went until the lever was touching the grip.

It might not hurt to see if your m/c does this.

The master cylinder has two seals or seal sets. One is the one on the piston that drives hydraulic fluid down the line that can fail to hold pressure, as you suggested. The other is on the input shaft that connects the pedal or lever to the piston. It seals fluid in and air out, and can fail to either one or both of these. The thing is that because one seal set is faulty, doesn't necessarily mean that the other is, so if a cylinder fails to hold pressure (leaks back), that does not guaranty that any air will get in. It does, of course mean the cylinder needs a rebuild in either case.

Get a brake bleeder, use some teflon tape on the bleeder screw and get it done. The way the calipers are built, then can trap air in them at certain angles. Thus you cannot get all the air out of them.

A mityvac vacuum bleeder will help you out. After you mityvac it, then bleed it normal and should be tight. If not, then you probably have torn the MC seals. Thus get a new MC kit and rebuild it.

Grey, so far we have just talked about the m/c. Do you see any possible way his caliper could be the issue?

I know on my older bike someone , who shall remain nameless, accidentally pulled the lever in when the pads were out. One of the pistons came out. I quickly shoved it back in. I sold the bike before I ever knew the final outcome on that one...

Thanks guys, I still have the caliper hanging from the ceiling, above the Master cylinder. I'm going to let it sit over night (with a zip-ty on the brake lever) and try tomorrow to see what happens.

By the way, I'm using EBC sintered pads, with a Galfer Stainless brake line, and Castrol GT LMA brake fluid..it says "Exceeds Dot 3 and Dot 4 specs".

Some have mentioned Bel-Ray as having some of the best brake fluid out there.....I'm assuming the Castrol is decent??

That reminds me....I also back awhile ago, tried the syringe trick pushing from the caliper to the Master Cyl.....didn't change a thing.

Have you tried a different lever? Yeah sounds kinda hokey, but I had a non-OEM lever (made by MSR) that I had to use as a spare at a race after being taken out in practice early this year that caused this problem for me. I went through all those steps, too. All I was able to get accomplished was a bunch of wasted brake fluid, time, and frustration. Somehow it occurred to me to change to an OEM lever and it took care of the issue. I guess the MSR lever is made a tiny bit different.... now i have an ASV C5 brake lever, no problems with it at all.

Good luck!

Grey, so far we have just talked about the m/c. Do you see any possible way his caliper could be the issue?
... it is nearly impossible for a caliper to allow air in without leaking fluid out.
...'63 through '82 Corvette rear cailpers excluded, of course.
...'63 through '82 Corvette rear cailpers excluded, of course.

my dad had alot of trouble with his on his '80...

Yeah, right now I'm using ASV levers for both the brake and the clutch (3 year model) I don't think it's the lever at all.

Have you thought about putting a master cylinder rebuild kit in? It rewally helped my older yz250f.

I bought a 200cc syringe and some 1/4 rubber tubing and made a reverse bleeder. This way you are pushing the fluid back towards the m/c (since air rises that way!). It forces the air out...it works awesome, usually on the first try.

Hope this helps:thumbsup:

The master cyl. kit may be the ticket. I already tried the syringe idea....didn't work.

Another way to bleed or freshen the fluid is to:

1. Take cap off of master cylinder (you will need to watch level closely)

2. Get a piece of clear tubing and make a loop, insert one end into a plastic bottle. Attach other end to bleeder screw.

3. Pump lever once and hold pressure, release bleed screw, release lever. Watch master cylinder level closely and keep it topped up as all fluid is changed.

4. Close bleed screw when 1/2 cup or so of brake fluid has passed.

You shouldnt have to do anything else but ride and enjoy.


look also at the brake rotor. After riding many hours the rotor can be dished. In the middle of the contact area is less material than on the edge. So the brake pads have first contact at the edge and then in the middle. Measure the thickness of the rotor at the edge and in the middle, maybe it´s dished. :devil:

The master cylinder rebuild kit from honda is cheaper. It drops right in. Slight difference in a small metal rod. The seals are the same.

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