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Vacuum brake bleeder recommendations?

Discussion in 'Bling and Appearance' started by The Snow Dog, Apr 24, 2008.

  1. Does anyone have any recommendations? It's just for 'home use' but I'm starting to do enough friends bikes these days that it seems worthwhile.

  2. Never used one .. are they that more effective than the old 'hose hangin in a bottle' method?
  3. Be careful. Because of the way caliper and cylinder seals work, it's possible to pull in air past the seal and you'll never get the brakes bled properly.

    That said, it should be quite effective as it should eliminate possible problems getting the master cylinder to prime, which is an issue that has driven me halfway insane on a few bikes.
  4. I have a Mityvac II vacuum pump kit which was purchased from Auto One for around $50 several years ago. It comes with a good collection of piping, adaptors and collection jug.

    Generally I use the kit in the old-fashioned way, but the vacuum pump gets used when there is a recalcitrant air bubble that refuses to come out. It doesn't happen often, but boy am I glad that I have the Mityvac when it does.

    I'd say that it's handy to have, but not an absolute necessity - perhaps something a group of friends can share around when it's needed.
  5. I use a short length of silicon hose and a 30cent 50ml syringe - no cleanup and you get a discount for buying a hundred ;)
  6. Vacuum bleeders can be a very handy tool. They are pretty much essential if you work on older cars where the traditional push-hold-bleed method may drive piston seals into rough/rusty/dirty parts of the brake slave/master cylinder, and the rapid, large movement may screw your seals up. If they're that bad, it's time to fix them properly anyway!

    PatB - if your seals are leaking that badly, it's time to reco your brakes. Air can leak past seals, but generally it shows that your cylinder walls were pitted or your seals are shagged.

    I use one of these:
    Expensive, but has a multitude of uses, including both vacuum and pressure bleeding, vacuum testing, carb balancing, etc etc. Expensive, but very useful! There are cheaper bleeders out there that do the job just as well, just fewer options.

    Only thing I can say - air does tend to leak around the bleed screw if you apply too much pressure. This can be resolved by a bit of teflon tape (difficult and fiddly) or some wick-in thread sealer/loctite can be used. Good old fashioned grease will do the job to...

    Hope this helps,


  7. My point was made more on the basis that the seals are designed to resist internal pressure pushing out rather than external pressure pushing in, which is what you get when using a vacuum bleeder. Seals are generally tapered so they will work much less effectively in a reverse direction, even if in good condition.

    Admittedly, the seals in modern calipers seem much less directional than those in drum brake slave cylinders of old, but the seals in my master cylinders still look like bicycle pump cup-washers to me so I'd be disinclined to trust them if loaded in reverse.

    I wouldn't claim it as a deal breaker against vac-bleeders. Just a point worth checking if someone's using one and mysterious air bubbles keep appearing, apparently from nowhere.
  8. That's true, and the older you get, the more this becomes prevalent. But I'd still argue that if your seals were leaking air using a vacuum bleeder, it might be time to replace them with fresh seals. If only because as brakes are released and pistons are forced back by springs attached to the linings, there would be a good chance that air could be drawn in as well (specially with ye olde drums). This is by no means a hard and fast rule though! So far I've found that most bubbles coming through when vacuum bleeding comes from around the thread of the bleed nipple and not the seal.

    It's one of the reasons I bought a bleeder kit that could also do pressure bleeding - the most difficult part about pressure bleeding is making a cap that can hold pressure in the master cylinder reservoir.


  9. As the owner of a lathe, a (crap) milling machine, silver soldering gear and a handful of scrap tyre valves, this does not present a problem :grin: . Haven't done it yet, because I haven't had to, but the thought is always at the back of my mind that I can if I need to.

  10. That sounds like someone I know! :shock:
  11. Thanks very much folks.
  12. Vacuum bleeding...

    PatB is right, you don't want to get air into the lines.
    What you have to be careful of is that the vacuum bleeders suck a lot of fluid at a time, and your reservoir has only a very small capacity, so it will be easy to suck it dry without realising it. The old way is the best way, a tube and an old bottle. Make sure that the end of the tube is completely submersed into the fluid at all times, and when you pump the lever, do it slowly keeping the top of the reservoir parallel with the ground.... it's all basic knowledge really....useful stuff....