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This One Weird Trick To Bleed Your Clutch


baraka

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Hello fellow VFR Enthusiasts!

Once upon a time, a long time ago, I was on a long meandering ride from Rochester NY to Philadelphia PA. It was unseasonably cold and my clutch fluid was probably low (yeah, I'm that guy who embarks on major road trips without checking all the vital fluids, I was young, and adventurous). 

Somewhere on the Delaware River I suddenly stopped getting response from my clutch. So I popped the old girl into neutral and coasted into a nearby NAPA. God smiles on fools. 

Over the course of the next four hours, I did my first clutch bleeding on the side of the road with my handy dandy underseat toolkit and a new bottle of brake fluid. I don't remember everything that happened, because it was a pretty wild four hours of improvisation, but I used a handy iPhone and this forum and a few others and nothing was working. Like most of the clutch maintenance/bleed threads, I was pumping and pumping the clutch handle and getting nowhere. 

Eventually I found a thread where someone had a little trick that I was desperate enough to try, and I tried it, and it worked. So naturally, now that I'm rebuilding my master cylinder, I went to find that thread and couldn't. But it worked beautifully, so I figured I'd post it here for two reasons: 

1. Nobody should have to go through the misery of bleeding this damn thing and getting nowhere

2. Maybe it's a really bad idea and someone can explain why. 

In short, I rebuilt the master cylinder, bench tested it to make sure it built pressure, reattached it to the handlebar, banjo bolted it in, and pumped it until I was getting fluid at the slave cylinder bleed port. 

At this point, no matter how many times I pumped and bled, pumped and bled, I was developing no significant pressure. 

This is where the fun begins - I undid the three bolts that hold the slave cylinder into the motorcycle, and pumped until the slave cylinder was pushed out as far as it goes. At that point, I squished the slave cylinder piston back into the slave cylinder with my thumb, resulting in a huge, audible bubble of air coming out of the reservoir on the handlebar. I did this three or four times until the bubbles were much smaller. Pump the handle until the slave cylinder is all the way expanded, then manually push the cylinder back, resulting in burping and bubbling from the reservoir. 

Once I was only getting small amounts of bubbles out, I reinstalled the slave cylinder, and was able to get serious resistance at the clutch lever and actually build up enough pressure to successfully bleed at the bleed valve on the slave cylinder. 

I've done this twice now on my VFR, and I can't find any other source online documenting this technique, so I figured I would share it here for wiser heads to determine if it's a good technique, if there's any way this could damage by slave or master cylinders, or maybe help some poor schmuck stuck on the side of the road out. 

 

I was working under pretty primitive conditions last night so I don't have any pictures, unfortunately. Instead, here's a picture of my last really bad idea so you can comprehend the general level of redneckery I'm comfortable with during maintenance procedures:

Cheers!

Really Bad IDea.jpg

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  • Member Contributer

Baraka, that sounds like a neat trick! 

 

The slave will displace a lot more fluid than the master so it basically pushes out air harder/faster. Never thought of this - thanks for the tip!  

 

Thinking about it, pumping the piston out pushes a lot more brake fluid into the slave than you can with it mounted. That will help get fluid “under” the air bubbles so it can be expelled upwards when you push the piston back in. 

 

Of course I’m just guessing here.

 

Bottom line - if it works I LOVE it!  

 

Perhaps it would also work with pumping brake pistons in-and-out?

 

Stray

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  • 3 weeks later...
  • Member Contributer

Pretty sure there’s a spring in the clutch cylinder that pushes the piston out. If you had that much air I doubt the master was doing much. Sounds like a good idea though. 

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2 hours ago, KevCarver said:

Pretty sure there’s a spring in the clutch cylinder that pushes the piston out. If you had that much air I doubt the master was doing much. Sounds like a good idea though. 

Yes, there is a big old spring. 

 

The endless pumping sounds like an un-primed/air locked MC. I crack the line at the upper banjo until a little fluid weeps out. This seems to help get fluid into the MC if it is fighting you, once you get enough to prime the MC you can push fluid down to the slave cylinder. That is the 'trick' that works for me at least, YMMV. 

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  • 2 weeks later...
  • Member Contributer
On 9/10/2018 at 9:50 AM, Lightduty said:

I’ve gone the easy route, I bought speed bleeders. Clutch and brake jobs are a breeze now.


Sent from my iPhone using Tapatalk

+1

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