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Discussion Starter · #1 ·
I have a pair of M4's that are several months old and work very well. Well, they did until I tried to bleed them yesterday.

(caution: home mechanic screw-up)

I bought a set of blue bore cap plugs and plug tools and I replaced the 4 original caliper black plugs with the blue ones. Before I did this however I removed all the brake fluid I could remove from the system thinking I would need to re-bleed (I realize now that was a bad idea). I removed the caliper from the brake line and let the line drip into a bucket and squeezed the lever til it was empty. Then I got as much fluid out of the caliper as I could with the bore plugs off. Once the blue plugs were in and the caliper was re-attached to the brake line I tried to add brake fluid back into the system and that's where the problem lies.

No matter how I try I cannot get brake fluid back into the system. I fill the lever reservoir (with Valvoline DOT4 - can't find 5.1) and slowly squeeze all the way to the bar but no fluid ever empties out of the reservoir. Is it air pockets in the line or the lack of a vacuum or what am I doing wrong?

Please help!!
 

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i had a problem bleeding the m4's predecessor - the enduro. at the end, i filled a saringe with dot fluid, attached it with a hose to the bleed nipple, and pushed all of it (25 ml) in.
a lot of the fluid got spilled from the reservoir, but so did all the air.
 

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Discussion Starter · #5 ·
I had the bleeder open most of the time but I did close it after a few unsuccessful tries at filling the system (yeah I know). I had a hose going from it to a bucket thinking that once the system was full of fluid the excess would drain off.

So far you've all given great advice! Thank you! I'll attempt it again once I get home tonight.
 

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I've had plugged bleeder valves, on cars, as well as my bike brakes. Air lock is entirely possible, as well. Try and attach a syringe to the bleeder after confirming it's open and then alternate between suction and pressure.

Another resolution I had was bleeding a system that resembled your system. I pumped the lever tons of times, spacing out reasonably, and after some time it moved. Looks like massive air lock in the line and/or caliper.
 

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Discussion Starter · #7 ·
Thanks for all the help, I finally got them bled using your (all of your) advice and now they are working perfectly again!

Another question - anyone else have a funny hole on the underside of their M4 caliper where it looks like a drill went into it? It's purely cosmetic but I'm just wondering.
 

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For future reference if anyone else is doing this, you can usually get it done without even needing to re-bleed. Remove the pads and lay the caliper flat on the floor (bore-cap facing up). Take the bore cap out, then pour fluid in until it reaches to the outer edge of the threads. When you put the new bore cap in it will overflow the fluid and you'll typically end up with no air in the system.

Larry
Mountain High Cyclery
[email protected]
 
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