Re:DIY Brake Bleeding via air tube, etc

[ajhuang@xxxxxxxxxxxxxxxxxxx (Andrew J Huang)]

David ziglin commented:

  > Yes, this sounds like a godd idea :
  > 
  > >|Get a 2" mountain bike tube ( about $2 at Walmart ) and cut it off about
  > >|10" on either side of the valve,  plug one end ( I cut the end off a

And then asked:
  > However, how then does one add replacement fluid or control air pressure?
  > Would it not be a good idea to connect the tube valve to an air tank or
  > even an air pump?  By that means one might be able to more delicately
  > control air flow into the rez, remove the bladder end to top up, and then

On the subject of air pressure, you want only about 10psi, much less
than most compressors can regulate.  That's why the inner tube is such
a good idea.  By the way, well equipped tool dealers can sell you a
professional pressure bleeder setup; 'course this costs a lot more
than the inner tube.

On the issue of refilling, David is exactly right.  It's a PIA to
release the pressure, remove the tube refill reservoir, reattach and
refill bladder.  However, it is so much faster than the two-person
"UP....DOWN.....UP.....DOWN" routine that it's insignificant.

If you really want to, it's not hard to take the bladder idea and
apply pressure to a large fluid tank which pumps the fluid into
the system reservoir.  The trick is to obtain a spare reservoir cap
and outfit it to,  a) have an airtight seal, and b) nipple to
introduce the fresh fluid.


David also wonders regarding:
  > This too seems like a good idea :
  > 
  > <<<<<I just push a good length of clear tube onto every brake nipple on
  > the car (usually 4, but 3 for Alfasud), and run them upwards a
  > the pedal upstroke it will only be fluid and not air.>>>>>
  > ...
  > ???  And most important, does this method guarantee that air will not pass
  > by the brake nipple threads and so be introduced into the system?

This has always been my problem.  With the exception of pressure
bleeding, I have never gotten good results with any of the one-man
bleeding setups.  I've tried the tube-up-before-down and several one
way valve systems but they've always been a PIA and with questionable
results.  No matter how you slice it, it's a pain to get under a wheel
to set up a bleed and then get out and do the pedal bit.  And if
you're garage floor is normal, like mine, you've got to change clothes
before you get in the car.

Pressure bleeding, in comparison, you set up the bleeder, and then go
from wheel to wheel and do the duty.  It works so well, that before
you know it, you've emptied the reservoir and have to do it all over
again!  Wear saftey glasses or goggles with pressure bleeders 'cause
they can spray in your eyes.

One other tool that is suggested is a hand operated vacuum pump
attached to the bleed nipple.  This apparently works as well as
pressure bleeding, except for the air past the threads problem.  Many
prefer this method.  One particular brand, "Mity Vac" is/was available
at Sears, around $40 +/- $10.  I've never used one.  (Vacuum guns like
this seem to be really useful, e.g. checking vacuum advance
distributors, vacuum controls on ventilation, power door locks, FI
diagnosis, deflating egos, etc).

- -andy

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