Lots of bubbles when bleeding clutch cylinder, presume seals are gone?

[lockwood77]

Been having a slight crunch engaging fifth gear at over 4k RPM, so decided to bleed the clutch as it\'s the easiest/cheapest place to start! I found that there was an almost constant stream of bubbles coming out and we put quite a lot of fluid through it, I\'m sure enough to fill the system between the reservoir and the end of the cylinder.

Can I presume that this will be the slave cylinder seals and that a rebuild kit is the way to go?

[shaunwil]

Not always the case. The thread can allow air to be drawn into the fluid being pulled out. If your drawing fluid out under a vacuum it is more noticeable. I\'ve PTFE taped the threads to stop the air being drawn in when using a hand pump. I had to do it on brand new master & slaves on the FB not too long ago.

If your in any doubt take the slave off and look for the fluid seeping past the seal to confirm.

Shaun

[lockwood77]

Hmm, I did notice a small amount of fluid on the end of the slave cylinder, which I\'m fairly sure arrived once I had loosened the nipple (i.e. not a leak). In which case, it was probably doing what you describe - pulling the air in as the fluid passed along, rather than having air in it in the first place.

Which is both a good and bad thing - good that the cylinder is probably OK, bad that I have a different gearbox issue!

[shaunwil]

Try sticking some ptfe tape on and see if it still bubbles first.

Shaun

[cyman]

try the old way of bleeding with 2 people. open bleed nipple, press peddle down and hold, tighten nipple. raise peddle. rinse and repeat. this stops any air being drawn inwards as the peddle is raised. do this a few times then pump peddle and see if its any better.

[lockwood77]

Ah, I wasn\'t doing the "tighten before lifting pedal each time" - only when I closed the bleed nipple (although I kept the end of the bleeding tube under the fluid so if anything was sucked back it was fluid, not air). Will try the PFTE tape and single pump/tighten method to see if it cures it.

[cyman]

you wont need ptfe on the thread if you were only getting bubbles on the thread when bleeding. only if it had been leaking before