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You're correct that the bleeding procedure using a Mityvac (which is what I use, too) is different from the other procedure you've heard about, the one that involves pressurizing the master cylinder. The Mityvac is a vacuum pump rather than a pressure pump -- it SUCKS the air out of the brake line rather than PUSHING it out.
Basically, you're doing the same thing either way -- driving the air-contaminated brake fluid out of the lines and replacing it with new non-aerated fluid from the reservoir, by creating a situation where more pressure in the reservoir than at the nipple. The pressure difference pushes down on the fluid in the reservoir so it flows through the lines and out the nipple.
The only difference in the two procedures is that with a "pressure bleeder," you're INCREASING the pressure in the reservoir while keeping the bleed nipple at normal atmospheric pressure. With the Mityvac, you're keeping the reservoir at normal atmospheric pressure while REDUCING the pressure at the bleed nipple.
I like the Mityvac approach because you don't have to worry about getting a perfect seal on the reservoir, and because it lets you do both the pumping and the opening/closing of the bleed valve at the same place, rather than having to run back and forth. (Make sure you keep an eye on the fluid level in the reservoir, though!) Just follow the directions with it and you should do fine.
I don't know what to tell you about the "bench bleeding" question. I've read that some master cylinder designs require bench bleeding, while others don't. When I rebuilt my Sonett's master cylinder, I didn't do it -- I just put it back in the car and bled the lines as normal, and it seems to work fine. The 99 cylinder could be different internally, so this doesn't invalidate what the other poster told you, but I think the 96 cylinder is more similar to a Sonett cylinder.
posted by 204.76.11...
, Mon, 22 Jul 2002 23:41:49
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