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biskino 13 Jun 2004 18:49

bleedin' brakes
Spring is in the air and, judging by the generally squishyness of my front stoppers, the air is in the brake hoses.

So, full of good intentions and limited knowledge I bled the front brakes on my bike yesterday (88 K75C). I've never done the proceedure on my own before but have helped mates with it - and hey, how hard could it be right?

Encouragingly, I had a couple of air bubbles come out through the bleed nipple off the calliper (I used the clear hose into a glass jar method - hose end submerged in fluid, careful to never let the resevoir get below half full).

But what threw me was that everytime I pumped the brake, tiny, champaign size bubbles came up into the fluid resevior through the piston intake for the master cyclinder. At first I assumed it was air coming up out of the system so I kept pumpin', got through 2 litres of brake fluid and it never stopped. Hmmmmm.

Being a pessimist I assumed that one of the o-rings or a gasket in the MC was leaking. I've never done this proceedure on my own so don't want to rush to any conclusions.

One thing that did occur to me (the next day, of course) is that when I was pumping the fluid through to bleed the brakes I left the cover off the resevoir - could it be the lack of back pressure that caused the bubbles to appear? http://www.horizonsunlimited.com/ubb/eek.gif

Any helpful advice, hints much appreciated - open mockery no doubt richly deserved. http://www.horizonsunlimited.com/ubb/redface.gif

[This message has been edited by biskino (edited 13 June 2004).]

Steve Pickford 14 Jun 2004 13:33

I've used a syringe & battery breather tube for the past 12 years. If possible, use a large syringe (50cc)with a thick tapered end to it. Stick the end of the breather tube in to boiling water for a minute to soften it befire pushing as far as possible on to the tapered syringe end. Fasten tigt with a cable tie if needed.

With a reservoir full of fluid, open the bleed nipple & attach the tube end to it. Starting with the syringe closed, gently pull the syringev open to suck fluid through. Keep an eye on the fluid level in the reservoir, top up as necessary.

With an empty reservoir, fill the syringe with fluid & squeeze very gently until the fluid is near the end of the tube. Attach tube to already opened bleed nipple. Squeeze syringe gently. This method will fill an empty caliper & then fill the lines before filling the reservoir. Once again, keep on an eye on the reservoir level.

If the fluid does not appear to flow through the system easily, remove the brake lever. I've had a couple of bikes where aftermarket levers held the m/cyl. piston slightly closed, thus blocking passageways & restricting flow.

All normal procedures for dealing with brake fluid apply as normal.

I emptied my K100 calipers last year to clean them. I bled both front calipers from empty in ten minutes max using this method.


simonrjames 14 Jun 2004 15:40

No being mechanically minded I was in the same position when I had a go at bleeding my brakes. With the pads pushed pretty much all the way out (but ensure that you dont push them out too far as the seals will pop out) try then to bleed them. If air is still trapped, with the lines full of fluid gentley push the pads back in towards the caliper. This should move any trapped air up the lines. Air naturally wants to go up and not down a line so this may make it easier.

biskino 14 Jun 2004 20:24

Thanks to both of you for your advice. So, it sounds like my Master Cylinder is safe and it's just air coming up out of the system.

I may give the syringe method a go - or plop down a few ££ on a product I've spotted on-line since posting. It's a brake bleeding pump (you can see it here) http://www.premiertools.co.uk/item4143.htm) - same principle as the syringe but possibly more suited to the mechanically challenged.

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