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VFR750 clutch issues

Discussion in 'Maintenance and Servicing' started by maduncle, Aug 20, 2012.

  1. Hi all,

    I have spent the last three weekends trying to get good even pressure in the hydraulic clutch line on my 1988 VFR750 but it is just not happenning.

    So far...

    1/. Replace the clutch master cylinder innards with a new kit.

    2/. Ditto on the slave cylinder.

    3/. Bled the system about a dozen times, keep finding air in the line tighten it all up and no lever pressure, no clutch operation.


    1/. I can hear a slight sucking noise coming from the piston in the master cylinder when I release the lever, is it sucking in air, in which case have I put it back together and not set the seals correctly?

    2/. There was a bit of corrosion around the rubber boot seal/snap ring are in the master cylinder - is this letting air in?

    3/. Is my clutch stuffed? I don't think so - it feels like an air lock, I just can't get it out.

    Next steps:

    I guess I could take the master cylinder off the bike (again) and check it is all together correctly - but I am at the #%&@ it stage and ready to hand it over to a pro - problem is I can't move the damn thing.

    So - does anyone know a mobile bike mechanic in Melbourne?


  2. Sounds like Concern 1/. is where it's at. If no fluid is leaking but air is sucking in, then that might help pinpoint the problem. I guess the lever side is a fair suspect.

    Any chance that the line to the slave is blocked or restricted, or that the clutch itself isn't releasing properly, causing negative pressure at the master? Shouldn't the clutch assembly normally be pushing the fluid back up when the lever is released, or are you not even getting the clutch to work a first time?
  3. Yeah - good point.

    Next weekend I plan to take the entire system off the bike, mount the lever on a spare set of bars in a vice in the workshop and bench test the hydraulics, that way I can see what the piston does when I use the lever.

    I might need to try and flush then prime the line too.
  4. Well, I got some good helpful advice from Gassit over the phone on what to do:

    1/. Crack open the banjo at the master cylinder slightly and pull the lever in a few times until there is only fluid seeping out.

    2/. Do the same on the banjo at the slave cylinder, then finally bleed at the bleeder valve.

    So we will see if this gets the air out.
  5. Solved it.

    I tried the Gassit method, and found no fluid coming from the master cylinder when I pumped the lever.

    So I took it all off the bike and stripped it down again, only this time I looked carefully at the assembly diagram and put the spring and rubber seal back in THE RIGHT WAY ROUND.

    Yep - I had the seal on the end of the spring going into the cylinder seal first, so all I was building was an effective method of retaining fluid in a master cylinder.


    With it now correctly assembled, I bled the line at the slave cylinder bleed point and had a fully working clutch in no time. I went for a half hour ride and all is good.

    Now - I will rest it for a few days and check the fluid levels before riding it later this week, because I am still not sure why it stopped working in the first place and there is a possibility of a worn slave cylinder piston or bore causing a leak.

    But - here's hoping...
  6. Goodo, see you Thursday.
  7. Fingers crossed...