Changing brake fluid - ok to have air under rubber diaphragm?

[bert_is_evil]

I'm planning on changing my brake fluid tonight, last time I did it I painstakingly tried to put the rubber diaphragm back in the reserviour without getting any air trapped under it - is this necessary? I know the fluid will absorb the water in any trapped air but is this a small enough amount to be insignificant?

[sinfull]

I wouldn't worry about being too pedantic about it !
Nor would i worry too much about replacing the whole resivour of fluid, it's ususally the lower few inches of line that gets heated up and it don't really circulate, so if ya just pump a few squirts out regular it should stop any possible brake fade !

You could wrap a rag around the resivour when you go to seal it up, slightly overfull so when you drop the diaphram in it forces a little out !

Best time to do this is when you put new pads in, cause if you fill the res. with half worn pads, then replace them down the track a bit, you will have to syphon some fluid out !

Edit or bleed them down a bit before replacing the pads

[bert_is_evil]

Cool, thanks for that sinfull

[kwaka_crasher]

I'm planning on changing my brake fluid tonight, last time I did it I painstakingly tried to put the rubber diaphragm back in the reserviour without getting any air trapped under it - is this necessary?

I can't believe anyone ever thought this was what you're supposed to do.

It's just an isolator from atmospheric air and moisture and it's flexible so that as the mechanical action of the piston displaces fluid there is no vacuum created in the reservoir - it simply allows that vacuum to be negated by the diaphragm being deformed with surrounding atmospheric pressure without introducing any external contaminants every time you apply the brake.

[The Pastor]

i can't believe anyone ever thought this was what you're supposed to do.

It's just an isolator from atmospheric air and moisture and it's flexible so that as the mechanical action of the piston displaces fluid there is no vacuum created in the reservoir - it simply allows that vacuum to be negated by the diaphragm being deformed with surrounding atmospheric pressure without introducing any external contaminants every time you apply the brake.

lol .

[bert_is_evil]

I can't believe anyone ever thought this was what you're supposed to do.

Since I wasn't totally sure at the time I decided to err on the side of caution, figured I'd feel like a bigger arse filling in an insurance form later because I screwed up my own brakes.

[kwaka_crasher]

Since I wasn't totally sure at the time I decided to err on the side of caution, figured I'd feel like a bigger arse filling in an insurance form later because I screwed up my own brakes.

Well, there is that. But I'd err even further on the side of caution and get someone who knows to show me because as the saying goes "you don't know what you don't know" and there are many ways to screw up brakes.

I'd normally change fluid only and always when changing pads primarily for the reason sinful outlined regarding level change.

lol .

I can't think of any simpler way to say it.

Too long in engineering I guess...