I use low air pressure, and since the hydraulic system is unpressurised and fluid you pump back in displaces fluid into the reservoir, i cant see how any damage could result, provided the brake lever is uncompressed&reservoir open.

MexicanGringo wrote:I use low air pressure, and since the hydraulic system is unpressurised and fluid you pump back in displaces fluid into the reservoir, i cant see how any damage could result, provided the brake lever is uncompressed&reservoir open.

Ahh i see an open system and low pressure. I didn't fully understand

Apologies for resurrecting an old thread guys, but I noticed at the end of a track day the brake lever was soft as s**t - it would almost go back to the bar (brakes applied, but was as though they were full of air) I only noticed as I entered the garage after the last session (was riding quite hard in this one), but have had no problems before or since...

The brakes were a nightmare to bleed prior to the day, and there are new pads (bedded in) and I'm 99% sure there's no air in the lines.

Will tie-ing the lever back a few nights then cracking banjo on MC a help? What does holding the lever back for a night do?

Am I overreacting and this is a problem with the fluid overheating or something? Standard DOT4.


It's probably nothing, and forgive my stupidity if its not, just Silverstone on Friday, and I don't want any surprises...

How old is the fluid? I understand that old brake fluid can let this happen (apparently the water content in the fluid boils and becomes steam, which compresses and 'softens' the effect of the fluid). A track day would ideal for creating this situation - hard braking, many times, during a track session is not the same as riding to the shops.

Thanks for the reply Chrissy,

The fluid is new!
Put all new pads, lines and fluid in just before Donnington - hardly done many road miles with the new parts.

What pads are you using?

I would probably tie the lever back overnight as this puts pressure in the system and forces air to evacuate the liquid. The same happened to my mate on his zx6 last Thursday and we reckon thin pads, shit brakes and not properly bled fluid caused the lever to come right back.

Standard Nissin HH ones, new-ish, still plenty of meat left on them!
Pretty sure the lines were bled OK, must of put a litre through, and use the ol' clear tube method, opening and closing the nipple combines with operating the lever, and all bubbles came out... and then I ran the collected fluid through again to make sure...

hmmm... and its odd that they were OK at the start of the day, isn't it?

with strapping the lever back - do I just cable-tie it... don't need to unscrew the res.cap or anything too?

I would bleed the master cylinder first. I had exactly the same thing, and i could have sworn i had bled all the air out, a week later cracked the banjo bolt on the M/C and hey presto air.

Good idea, I'm pretty sure I did this, but I'll just pump and crack and pump and crack a couple of times. Seems ok tonight, but then it is static...

Could have dislodged an air bubble trapped in the system that has made the bike feel worse..