Bleeding clutch hydraulics

[Constant Mesh]

I've read about two techniques for bleeding the clutch hydraulics. The Yamaha manual discusses actuating the lever a few times and with the lever held in to the grip open the bleed screw and let fluid and bubbles escape. Close the bleed screw and repeat until no more bubbles. Top off the master cylinder as needed.

My Honda car manual discusses another simpler technique. Attach a clear tube to the bleed screw with the tube emptying into a container containing brake fluid. The end of the tube will be immersed in the fluid keeping air out. Open the bleed screw and operate the clutch pedal slowly back and forth, topping off the master cylinder as it empties. Continue until no more bubbles appear in the tube. Close the bleed screw and top off the master cylinder.

Don't know which technique is better or quicker?

If the fluid is under pressure (bleed screw closed) do the bubbles all migrate to the slave cylinder? Is there a pressure gradient from the master cylinder to the slave which propels the bubbles toward the slave as the piston moves the fluid?

 

[garyahouse]

First method is easier and quicker. Simply squeeze the lever, open the bleeder nut just a little until you feel the lever go down. When it hits the handlebar, close nut, and repeat. It's that simple. Don't worry about all the junk you read. It takes all of 10 minutes. Make sure to use fresh fluid, not some junk left in a bottle for years in a hot garage... and don't let that master cylinder go dry as you use up the old fluid. Google search:

site:fjrforum.com clutch fluid flush

Gary

darksider #44

 

[RossKean]

+1 to Gary's reply

Don't overthink it. Easy service to accomplish in a very short time.

I suspect the speed-bleeder/Mityvac bunch will chime in but I have never felt the need.

 

[Fred W]

Any method will work fine for exchanging old fluid for new, assuming you don't introduce any air in the lines. When you get air in the clutch lne it can be a bitch to get it out because the lines are nearly vertical and fairly straight. Even when compressed, the air bubbles are a lower density (lighter) than the brake fluid, so they always have a tendency to rise up as you try to flush them down. So, the faster you can move the fluid down and out of the slave the better chance you have of flushing that air down and out. Based on that, the "Honda" technique you describe would be more effective at getting air bubbles out.

I use a MityVac for all of my bleeding (brakes, clutches, bikes, cars, etc.) I find it easier to use than the open/pump/close routine and as long as you keep the reservoir full you'll never introduce any air. An even better way to do it is to force fluid in at the bottom (slave) and push the fluid back up into the reservoir, which is the direction that the lighter air bubbles want to go anyway. There are some tools available that will do that, I do not have any to recommend.

Another old trick for clearing the last little bit of air from hydraulic lines is to pull in the lever and tie it to the handle bar overnight. This compresses the bubbles, making them smaller with less surface area to stick to the inside surfaces of the hydraulic lines. The bubbles will gravitate up to the master cylinder (you can tap on the lines to help speed the process) and when you release the clutch lever in the morning they'll be sucked back into the reservoir. This has helped get those last few bubbles out for me a few different times.

 

[Constant Mesh]

I changed the clutch master cylinder on my Honda car Sunday. There's some air in the system and I'm having trouble getting it out. I should have filled the new MC with fluid before installing it but I didn't. I used a mity-vac at the slave to replenish the fluid. The system has a u-shaped flex hose between the body and the engine. I'm wondering if the air bubbles can't cross the u-tube divide because I'm not moving the fluid in big enough quantities and rapidly enough.

If I connect the mity-vac to the hose between the reservoir and MC up top and then add the fluid at the slave will this get all the bubbles out? Bring a wall of fluid up and move the bubbles higher and higher, eventually through the MC and into the mity-vac?

If I move the mity-vac up top should I use the bleed screw to introduce new fluid or should I disconnect the line at the slave and draw the fluid directly into the line bypassing the slave?

 

[Fred W]

The tough part about doing that is twofold: Not letting any air in at the slave end (those nipples leak air notoriously) and not getting air in the line where you break it at the master cylinder end.

Here's the kind of pressure tool that is supposed to let you reverse bleed by pushing the fluid up from the bottom: Motive Pressure Bleeder or you can make a "home-brewed" one from a pump garden sprayer.

You'll need to seal the bleed nipple threads on the slave end with teflon tape and then suck the fluid out of the reservoir to give the fluid somewhere to go.

 

[garyahouse]

+1 on Fred's comments (you da man, Fred)

When/if you do get air in the lines, which is rare, his comments are spot on. I use a MityVac on mine as well. Keeps a continuous suction on the system. Hook it on the bleeder, squeeze the handle a few times to crank up the suction, open the bleed valve and let it do it's thing, while ya squeeze the pump handle a few times to keep the pressure gauge happy. When the fluid gets low in the reservoir, close the bleeder, refill the reservoir, and continue the process. Very simple to do. Harbor Freight has these things cheap... not that you really need one. The description in my original post will work just fine if you're just changing fluid and are not worried about air bubbles. You might want to read up on brake fluid 101 from this forum here CLICKY

Gary

darksider #44

 

[Constant Mesh]

I'd empty the reservoir first and then disconnect its gravity flow hose. I'd connect the mity-vac to the hose removed from the reservoir. I believe this technique would work OK if I don't introduce additional air at the slave end. If I bypass the bleed screw and introduce the new fluid directly into the slave's supply line I shouldn't introduce any additional air.

 

[Fred W]

Yeah, that should work fine.

 

[creg-ny-baa]

O-Tay. Minor detail for the inexperienced: a vigorous stroke on the lever with the clutch reservoir cap off may result in a geyser of DOT 4 that will defy description. DAMHIK.

 

[Bounce]

BTDT (as have many others). Clean it up quickly and completely. It eats up paint like a bitch.

Another easy method is to use a MityVac. Inexpensive and fast for 1 person to do. The more difficult part is keeping the reseviour full (which isn't hard, just requires keeping an eye on it).

Or you could go MONDO-MityVac and amaze your friends and family.

 

[bramfrank]

I'll represent the Speedbleeder contingent:

https://www.fjrforum.com/forum/index.php?showtopic=137835

https://www.fjrforum.com/forum//index.php/topic/137581-clutch-and-brake-fluid-flush/?do=findComment&comment=855616

 

[creg-ny-baa]

I'm all in on the SpeedBleeders; installed them all around yesterday. The location of the bleed on the clutch slave is unfortunate; having to at least move the fairing outward to access it isn't hard, just a nuisance. I have a MityVac too. My experience on those is that they tend to suck air past the hose, so it's tough for me to tell when I'm pulling air-free fluid. Someone mentioned on another thread the idea of dropping a single-edged razor blade down into the reservoir to act as a block to the eruption. I like the idea; you'd just have to be careful to a) take it out, and B) not drip when you do.

But, it's done, and everything seems to work.

 

[RaYzerman19]

O-Tay. Minor detail for the inexperienced: a vigorous stroke on the lever with the clutch reservoir cap off may result in a geyser of DOT 4 that will defy description. DAMHIK.

Fixed by dropping in a Canadian quarter into the reservoir on top of the hole. Fits nicely. Canadian quarters have real metal in them so you can fish it out with a magnet when yer done.

 

[Bounce]

Since gold and silver are non-magnetic (and still qualify as "real"), I guess that you meant the Canookie Coinage has ferrous metal in it. Steal? Iron?

 

[RossKean]

Since gold and silver are non-magnetic (and still qualify as "real"), I guess that you meant the Canookie Coinage has ferrous metal in it. Steal? Iron?

Nickel is also magnetic.

 

[Bounce]

So falls under the "ferrous" umbrella I mentioned? Gotcha.

 

[crumpadump]

I placed a nice size bolt screw in there (after I got a burp of dot4 come out and then remembered Razermans suggestion), kept everything in its place. I'm also a big proponent of the speedbleeders now!

 

[RossKean]

So falls under the "ferrous" umbrella I mentioned? Gotcha.

A ferrous alloy is one that contains iron. Not necessarily magnetic (i.e. most 300 series stainless steel are not magnetic but contain over 70% iron (+ Cr, Ni, Mn etc)). On the other hand, a ferromagnetic material (like pure nickel) does not have to contain iron but is attracted by a magnet.

Semantics? Correct definition? Does it really matter? Does anyone really care?