Motorcycle Master Cylinder?

Hello. I have a 2001 Vulcan 1500 classic I bought cheap as a project. It has been sitting a very long time. I have everything fixed except one issue.

I thoroughly cleaned the master cylinder for the clutch and the slave cylinder and blew the line out and bought and installed a rebuild kit for the master cylinder and I’m still having the same issue!

After about 20-30min of riding the clutch will start to slip until eventually you have no clutch at all. This is because the line is getting pressurized and holding the slave cylinder in. I’m leaking no fluids. My reservoir is filled half way on the sight glass as I overfilled it once and thought that may have been the issue. It’s not. 

The master cylinder sleeve did have a couple nicks in it but nothing that looked deep or Catastrophic.

When I open the bleeder screw at the slave cylinder I get my clutch back 100% which makes me feel the slave cylinder is probably fine. 

Any opinions? A new master is expensive.

7 Answers

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  • Anonymous
    2 months ago
    Favourite answer

    The clutch master cylinder compensating port is likely clogged   When the clutch fluid gets hot, the fluid expands and the port allows fluid to go to the reservoir.  If the port is clogged, fluid has no way to go but build pressure. 

    Clean the port with a tiny drill bit or a piece of safety wire.  Bench bleed the master cylinder after cleaning.  Good luck

  • 1 month ago

    you should be able to fix the one you have.

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  • Anonymous
    2 months ago

    Sounds like the slave is sticking. Blow it open w/an air tip. Use 1000 -grit wet or Dry wrapped thru  a 3/16"  slotted dowel, doubled back so Grit sides are out,wire the end shut; to hone it out. Chuck in drill; at low speed,  move rapidly in and out, just a Few seconds, until  U see honing  marks. Clean Well w/brake cleaner,   wipe, use a  little brake lube on seal. Master can be honed, too.

    You may want to Soak master in that dunk 'em  type carb cleaner, too. Blow out all passages w/air tip or  aerosol can with  red nozzle  of carb or brake cleaner. 

     

    You may not have bled it right. Bleeding requires the lever be about 3/4" from bar. Use a piece of wood and wire it on. Make sure master  full, then, put a  500 CC syringe and  1/8 " vacuum line to bleeder. Open bleeder, suck fluid out until   level  drops to Just above  holes in master, close bleeder. Refill  master (Dot 4)  U may have to reverse bleed:Suck out fluid in master until just above holes; fill the syringe  with DOT 4,  Hold it Up  so  bubbles at Top; open bled nipple and  force fluid thru it..  May have to do this  several times.Do not allow master to oveflow and ruin paint, suck excess out. 

    syringes cheap  at feed stores.

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  • Scott
    Lv 6
    2 months ago

    Those can be tricky. If I remember right, there is a small check valve on the master cylinder that can really get gunked up. Go to a forum like Vulcan Baggers and do a search or ask for advice. I'd be surprised if you needed a new master, you should be able to fix the one you have.

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  • 2 months ago

    Look at any adjustments in the clutch lever, that could affect how far the piston travels in to (or rather releases from) the master cylinder.

    When the clutch is fully released, the master cylinder piston must be far enough out to expose a port that connects to the reservoir.

    Look for the other end of the port in the inside of the reservoir and check that it is clear and open through to the cylinder.

    If everything is set properly, it only closes off just after the master cylinder piston has started to move, so the clutch line and slave cylinder are vented to the reservoir when it's not operated.

    If the adjustment is slightly wrong and that port is never opening, the pressure can build up in the clutch line.

    • ...Show all comments
    • Road warrior
      Lv 4
      2 months agoReport

      Any "adjustments" won't change so much with heat; the hydr. fluid is expanding From heat at slave and causing back pressure to master which can't compensate and/or slave is rusty and sticks. 

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  • Anonymous
    2 months ago

    By that age lines will start to bulge, look for signs of cracking around any routing clamps on the hose.

    • Road warrior
      Lv 4
      2 months agoReport

      Bulging. leaking lines wont build up or hold pressure. 

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  • 2 months ago

    Sorry, a new master should solve the problem.

    Source(s): Riding/racing/wrenching for 55+ yrs
    • Anon
      Lv 6
      2 months agoReport

      More likely slave sticks. 

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