Bob Tufts <rbt@itc.Kodak.COM> sez:
>I bought a vacuum bleeder last year (can't remember if it's an "EZ-bleed")
>and have noticed in using it on my Lotus something odd. It seems I have leakage
>around the threads of my bleeder screws.
This seems to come up regularly on the various auto lists and newsgroups.
The usual response is that you should put a turn or two of Teflon tape
around the threads of the bleeder screws. Takes care of the vacuum leak,
and gives you extra insurance against one of them freezing into place.
>Under this situation, it would be better if I had a
>pressure bleeder attached to the master cylinder.
As I have written here before, there is a definite physical advantage to
using vacuum rather that pressure with respect to the amount of air
dissolved in your brake fluid. The solubility of a gas in a liquid is
directly proportional to the pressure. Pulling a vacuum on brake fluid will
actually pull dissolved air *out* of the fluid. That's why there are no
bubbles is a sealed bottle of pop, but when you open it, you lower the
pressure on the system, and all kinds of gases escape from the solution.
When racers talk about the brake fluid "boiling", it's not really boiling.
The boiling point of brake fluid is higher than the brake lines and
cylinders are likely to get, especially under pressure. It's just that as
the temperature rises, the solubility of a gas in a liquid *decreases*. So
when the brake fluid gets hot enough, even under pressure, the dissolved
air comes out of solution and forms bubbles in the fluid. Not good.
The ultimate way to prepare brake fluid would be to heat it up, under
vacuum, before injecting it into the system. Come by my lab sometime and
I'll demonstrate. You'll be amazed at how much dissolved gas comes out.
Lee M. Daniels - Laboratory for Molecular Structure and Bonding - Texas A&M
daniels@lmsbvx.tamu.edu | DANIELS@TAMLMSB.BITNET | (409) 845-3726
|