Pressure Bleeding your Brakes

["Steve D'Gerolamo" <steved3@xxxxxxx>]

Pressure bleeding works best when the pressure comes from a storage
tank...this can be via your shop air compressor, a portable storage tank or
even a spare tire.  It does not work well from a bicycle pump (especially
if you're trying to do the distant rear cylinders/calipers...not enough
volume under the cap to push the fluid through) or a portable air
compressor (the kind you plug in the lighter for emergencies). As you do
not have a compressor or portable tank, try using a spare tire with the
pressure deflated to 20psi.

		I am copying the BMW digest in case others have had this problem.  SD
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At 09:36 PM 11/29/98 -0600, you wrote:
>
>	Hi, Steve
>
>	I bought one of your nifty-cool red anodized replacement caps for my
>master cylinder on my BMW 750iL.  I was planning on swapping out the
>brake fluid with some of your Super Blue ATE fluid.
>
>	Well, as a trial run, I decided to try it out on a '90 VW Golf that I
>bought yesterday.  The rear wheel cylinders were shot, and it needed a
>brake fluid change.  So, I thought, I'll just go ahead and use my
>pressure bleeder cap, because the Golf has the same kind of ATE master
>cylinder (very convenient).
>
>	So, off comes the cap, in goes a rubber bulb pipette, and I sucked out
>all of the old, bad fluid.  In goes some new Valvoline Synthetic brake
>fluid (not a silicone, but a synthetic glycol, 500 degree boiling
>point). 
>
>	On goes the new red cap.  I used a bicycle pump as my air supply.  I
>pressured it up to 20-30 PSI, and opened the bleeder screw on the rear
>wheel cylinder.  
>
>	Nothing happened!
>
>	If I pumped the brake, I could force fluid into the wheel cylinders. 
>But no matter how I tried it, I could not convince the fluid to move in
>just by using the air pressure trapped inside the cap.  I know it was
>holding the pressure, because when I released the cap, I heard it woosh
>out.  
>
>	I experimented with having my assistant hold the brake pedal slightly,
>or even quite a bit, and no luck, it had no effect.  The only time fluid
>moved was when I pumped the pedal, and a tiny amount would come out.
>
>	In any case, I had to bleed the brakes the old fashioned way, by
>pumping the pedal.
>
>	What am I missing here?  I thought the idea was to hook up an air
>supply (not too high pressure) and that it would force out the old fluid
>just by opening the bleeder screw.
>
>	I am holding off on the BMW job pending clarification.
>
>	Thanks,
.
=========================================
Steve D'Gerolamo - The Ultimate Garage
201-262-0412 / steved3@domain.elided / http://www.ultimategarage.com

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