Cap off when bleeding brakes/pedal-pump clutch bleed?

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06-13-2010, 01:48 PM

#11

MOOK3456

4th Gear Member

Join Date: Mar 2010

Location: over yonder

Posts: 1,185

Quote:

Originally Posted by CliffyDeuce

The big reason to have the cap on while you're bleeding the brakes is to minimize the exposure of the brake fluid to ambient air. Brake fluid is hygroscopic, so it'll absorb water out of the atmosphere if left exposed to the air. Obviously, this is much worse on a humid day, but typically, water in the brake fluid is one of the main reasons it needs to be bled and/or flushed as often as it does (assuming you don't track the car), so it make sense to minimize the amount that gets absorbed to begin with.

Just my 2 cents...

If you leave the cap on how are you supposed to see the fluid level and prevent it from sucking air once you remove it to refill? I dunno how most of you do it but I've always done it cap off and kept it topped off with new fluid as I go. As far as moisture in the fluid...The only part that would absorb any if this is even true is the very top layer of the fluid and as you're topping it off, the 5min max that the top layer is exposed isn't going to hurt anything, either way you have to remove the cap to refill anyways.

Here's a helpful link for ya OP-

http://www.corral.net/tech/maintenance/brakebleed.html

Last edited by MOOK3456; 06-13-2010 at 01:54 PM.