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Hard of understanding. Front brake.


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I've recently been battling with a spongy front brake on my '05 450EXC.😏

I have managed to get it "something like" and will live with it for now.:ride:

My question is.........I can't get my head round the theory of zip-tying the lever back over night resulting in a good brake in the morning.🤣

I'm not saying it doesn't work, I've read many reports of success.😏

It never seems to do any good for me though, and further more I can't understand how it would.🤣

Can some one please enlighten me as to how the air manages to get from the hose side of the master cylinder piston back into the reservoir when the lever is pulled tight in. Surely the passage is shut off.

Like I said, I'm not saying it doesn't work, I just thought it was about time I asked how it does work.

Your thoughts greatly appreciated.:cheers:

Andy.

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Every time we apply the brakes and the piston of the caliper slides in & out very slightly some minute amount of air gets into the hydralic system. In a perfect world gravity takes it upstream where it bubbles to the top of the reservoir. For this to work the high point of the system must be the reservoir! On the SX models it is, on the EXC the hose is somthing like 2" longer to go over the headlight. IF you park your bike on the side stand, leaned left and handlebar turned left no problemo, master cylinder is the high point. Park it on a stand upright and bar square, the high point is over the headlight and an air bubble will develop there.

Your correct in your analisis that while zip tied the air can not get to the res, all I can figur is the air gets up to the piston in the master cylinder, then when you in tie the brake it goes on up to the top. Strange system but it does work as does the trick of putting your knee on the calliper and pushing it in so most fluid goes up, then you pump it back down. If you always store your bike bars turned left you can forget about those two methods

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all I can figur is the air gets up to the piston in the master cylinder, then when you in tie the brake it goes on up to the top. Strange system but it does work

Thanks Dave.

I don't dispute it seems to work for some.

Just wanted to understand the theory.

Still not sure of the significance of ziptying the lever overnight though.

Sorry if I'm a bit dim.

Andy.

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The lever zip ty method has worked for me. My theory on why it works is that the constant pressure it puts on the system forces any bubbles to work their way to the resevoir-especially when following Dave's suggestion of letting the bike rest on its side stand with the bars turned left so the resevoir is elevated (just my theory).

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i haven't heard a definitive answer that i wud hang my hat on but pressurizing the system(pull'n the lever) will compress the bubbles make'n them smaller possibly allowing them to move up the lines more freely? 😏

😏

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MAYBE? The system being under constant pressure from the zip-tied lever causes the tiny air bubbles to be absorbed into the oil. Of coarse this would only be a temporary fix but may allow the aerated fluid to flow easier to the MC where the air can escape. Depending on how much air is trapped in the system may determine how it works for some people and not for others.

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it has seemed to work for me..again no explanation why from me...for me, just to make sure my m/c is the high point on the line i just put a short bunge to the front fender around the ft.brake line...taking out the high arch of it which for sure make the master the high point...

any GOOD bleeding will solve the problem tho....

i really like dave's idea of pushing on the caliper to back bleed.

i will use that way next time...i would take the cap off of the m/c and bow the line down with a bungee just to make sure you have a constant upward plane then push the caliper...make sure you keep the master full when youpump the system back up

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  • 2 weeks later...
  • 2 months later...

One other thing to mention, I tried everything I could, rebuilding the MC, bleeding with Dave's method, on the bench with absolutely no air in the system and I still had spongy brakes........

then I came across an old post on KTMtalk that mentioned the pin that is in the brake lever being too short and not stroking the MC piston far enough in and out to keep the air moving out and keep the fluid in the piston bore. So, even though I didn't think it could be possible I grabbed the pin from an old bent up clutch lever and by golly it was longer. I put the clutch lever pin in the brake lever and one finger brakes were restored in all their glory.

BTW, this is on my 05 MXC, so maybe there was a problem there:excuseme:

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One other thing to mention, I tried everything I could, rebuilding the MC, bleeding with Dave's method, on the bench with absolutely no air in the system and I still had spongy brakes........

then I came across an old post on KTMtalk that mentioned the pin that is in the brake lever being too short and not stroking the MC piston far enough in and out to keep the air moving out and keep the fluid in the piston bore. So, even though I didn't think it could be possible I grabbed the pin from an old bent up clutch lever and by golly it was longer. I put the clutch lever pin in the brake lever and one finger brakes were restored in all their glory.

BTW, this is on my 05 MXC, so maybe there was a problem there:excuseme:

You grabbed the pin from a Magura clutch lever?

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