Brake Fluid Resevoir Diaphragm and level check

Sorry to start a new thread... i did some searching and found bits and bobs, but i just want to get some definate answers/opinions.

When filling brake fluid into the handlebar resevoir, how do the fill level lines work? I gather the markings on one side are for when the bike is on the stand and the other is for bike level? Which is which, and is this with the bars turned/locked?

The reason i have a problem here seems to be the diaphragm under the lid, mine is totally expanded... i assumed this was to dampen the fluid and make sure fluid was always available at the supply line. However, i now beleive this diaphragm should be collapsed upon refill? So it can then expand?

I will be totally re-doing my front calipers on saturday, so i could do with knowing the answer to those 2 things in time for that.

Re-collapse the diaphragm and fill the fluid to in the middle of the two lines and then check the level with the diaphragm refitted.

[jambo]

You want the brake fluid reservoir level when you're filling it or opening it, this often ends up being with the on a paddock stand with the bars straight ahead, or with the bars full-lock right with the bike on the side-stand. Use your eyes


When you take the lid off and the rubber out, just flatten the rubber again gently with your fingers, it should pop back into shape.

Be aware the brake fluid is probably low because the pads have worn, the pistons have move further out to take up the space, and the fluid has been needed to fill the void behind them. In short, don't fill the reservoir up, and then push all your pistons back in, as you'll end up with the fluid over-flowing out of the reservoir.

Use your eyes and your head and you won't go far wrong. Any spillage to be wiped off quickly.

Jambo

[yorkie_chris]

Originally Posted by jambo

In short, don't fill the reservoir up, and then push all your pistons back in, as you'll end up with the fluid over-flowing out of the reservoir.

Or dragging brakes.

dragging brakes?

[yorkie_chris]

Yeah, if you fill it up, then push the pistons back to replace the pads, then it will build up pressure in the reservoir and the brakes will always be on a little bit. Will wear your pads down quickly and generate excess heat. Can cause brake fade, warped discs etc.

[yorkie_chris]

If fluid level is low, then either you have a leak, or your pads are worn basically. Check those things before just topping the fluid up to the top.

[jambo]

Originally Posted by yorkie_chris

Yeah, if you fill it up, then push the pistons back to replace the pads, then it will build up pressure in the reservoir and the brakes will always be on a little bit. Will wear your pads down quickly and generate excess heat. Can cause brake fade, warped discs etc.

Possible, but only if you don't undo the reservoir cap when pushing the pistons back, and the reservoir is completely air tight so can't let any pressure out, and was over-filled in the first place.

Originally Posted by yorkie_chris

If fluid level is low, then either you have a leak, or your pads are worn basically. Check those things before just topping the fluid up to the top.

Certainly worth a check, but may just mean that the last person to change the pads didn't fill it all the way up to the "upper" line. It's a useful point of reference, but only if you know where you started from.

Jambo

[yorkie_chris]

Originally Posted by jambo

Possible, but only if you don't undo the reservoir cap when pushing the pistons back, and the reservoir is completely air tight so can't let any pressure out, and was over-filled in the first place.

Aye, but it is a common mistake to make.

i can't beleive anybody would be strong enough to compress the system!

thanks for the tips though, i will refit the diaphragm in compacted form. It is not that i have noticed a low level, it is because i recently refilled the fluid.