It should be bleeding obvious

[ribbert]

I think about this every time it's posted.
Can someone explain to me why fastening the clutch lever to the bar overnight helps with bleeding?

Noel

[fj316]

This is just speculation and I've yet to do it myself but I suspect that as long as the clutch is not leaking you put a constant pressure on the fluid so that the air bubbles trapped in nooks and crannys is slowly forced upwards to the bleeding point and thus escapes throught the bleeding valve. Also the fluid stays still while the pressure is applied as opposed to when pumping so all the teensy bubbles that might permeate the fluid congregate to larger pockets of air.

Just my two kroners worth.

[keand3]

Just my two kroners worth.

Amen to kroners.... Never have enugh of them... 

[JCainFJ]

Brake fluid absorbs quite a bit of air (or one of the gasses that make up air), and fastening the clutch lever to the bar (raising the pressure on the system) can cause some of the small air bubbles to dissolve into the fluid. I have removed this absorbed air by placing new brake fluid in a vacuum chamber and evacuating it several times. Using the degassed brake fluid provides a firmer feel at the lever and makes bleeding easier too. I do not know for sure, but I think brake fluid likes to absorbs Oxygen which makes up about 21% of air at sea level.

[FJ111200]

I think about this every time it's posted.
Can someone explain to me why fastening the clutch lever to the bar overnight helps with bleeding?

Noel

It doesn't help at all.   It's fantasy dreamed up by someone who can't bleed up in the right way.
All the posts aboput bleeding clutches and brakes, with a gizmo called this or that is nonsense.
I just use the finger and thumb method everytime and it takes about 5 to 10 minutes to bleed the whole set up, and that's from dry.

[skymasteres]

I've definitely noticed greatly improved brake lever feel after using an old mini-fridge motor to pull a vacuum on the brake bleeder while bleeding. Between that and jiggling the lever all the air is worked out quickly.

[jscgdunn]

"Finger and thumb method"...do tell!  Always interested in a simple approach.

Thanks,

Jeff

[FJ_Hooligan]

Seems like the method is recommended whenever someone is having trouble bleeding the system.  In that case, pulling the lever to the bar would produce negligible pressure in the system.

Plus, when the lever is pulled, the path back to the master cylinder is blocked so any air that rises would still be trapped until the lever was released.  Seems like the same bleeding would be accomplished by just walking away from it overnight.

Hooligan

[FJ111200]

OK, i have posted this before, but here go's again,
so you've got a totally re-built system, no fluid, fill the reservoir, crack open the banjo or the bleed nipple and remove completely, then put you finger over the hole or your finger and thumb if you've taken a banjo union off a hose, hold it there and pump the lever a few times, release your digit and you will hear a sucking or popping sound, this is the fluid starting to travel out of the reservoir down the hose, after a short while of repeating this procedure a load of fluid will come out of wherever has been held by your digit, now put the bleed nipple or banjo bolt back in and start to bleed up with the tube off the nipple in the jar, don't forget to keep topping up the reservoir.
Works everytime, don't be fooled by magic gizmos and hold the lever bollocks, honestly.

[jscgdunn]

Thanks ...makes sense. 
I keep the tube attached the bleeder elevated above it so it fills with fluid and eventually pumps into the jar.  It usually a matter of pumping the air out.  I flushed two FJ clutch masters in the last two weeks this way with no issues.

Jeff

[Dan Filetti]

Can someone explain to me why fastening the clutch lever to the bar overnight helps with bleeding?

It's the placebo effect.

Dan

[Travis398]

As I said a couple days ago I was skeptical about this zip tie method but seeing is believing.

A friend of mine put a zip tie on his front brake lever, not to bleed the brakes but to keep the bike from rolling in the trailer.
After he cut the zip tie and unloaded the bike he said his front brake lever never felt so good.

So just a couple weeks ago I changed my front calipers, I bled them till no air was coming out of the bleeders and had a good pedal (lever)

So just for the F@#K of it i put a zip tie on my lever for the night, and sure as shit the next day the lever was much tighter than it was the day before.

so those of you that think it's bullshit have obviously never tried it. 

I know I didn't answer the question, and didn't have any great words of wisdom, or scientific formulas to back up my theory but I do know it works. 

Try it, you'll like it

[fj11.5]

Maybe the air bubbles do float up some  , can't see throuh the line to tell,  but once the cable tied lever is released, perhaps it pulls the air And fluid that's rissen?  Up to the top,out into the master 

[andyb]

Simple time, letting the bubbles settle to the top.  

When you pull the lever, you're actuating a little piston.  Pull the lever in just a tiny bit while watching, and you'll get a face full of brake fluid.  This is because the master cylinder resevoir is open to the rest of the system when the lever is fully away from the grip.  When you pull the lever in, it tries to raise the pressure in the system, but the bleed to the space above is still open, so it squirts out the top and into your face.  Keep pulling on the lever, and that bleed is covered up as the seals pass by.  At that point, it's a closed system, from the master cylinder's piston seals down to the slave.

So, pulling the lever in to the stop and walking away leaves you with a closed system.  No big deal.  Walking away for a few hours lets the tiny bubbles migrate up through the slightly thick fluid (thick compared to say, water), until they're resting against the piston seals.  When you then undo your lever and let it release, they cheerfully shoot up into the resevoir, and the next pull of the handle shoves fluid in, rather than air.

This is why when you bleed the system, you really only need to move the end of the lever an inch or so if that, but most people will persist in bringing it all the way to the bar, making themselves tired and cranky for no good reason.  It's really not a particularly difficult system to bleed, but it can be a bit twitchy to prime the master so that it moves fluid rather than air.  It's a little like trying to pour water into the top of a glass rather than starting at the bottom, a tiny fraction at a time.  I think people have difficulty with it because they make it a lot more work than it really needs to be and give up early because they are wasting most of their energy and not really getting anywhere with it.  I don't even open the bleed at the slave until I've gotten some headway made on getting the system mostly full of fluid, because the air is going to naturally want to go out the top, rather than shoving it out the bottom.  Once you've got the system working but still mushy, that's when it's time to open the bleed at the bottom and start shoving fluid through gently.  Brake fluid is slightly thick stuff and doesn't want to be forced through like water!

[oldktmdude]

Simple time, letting the bubbles settle to the top.  

When you pull the lever, you're actuating a little piston.  Pull the lever in just a tiny bit while watching, and you'll get a face full of brake fluid.  This is because the master cylinder resevoir is open to the rest of the system when the lever is fully away from the grip.  When you pull the lever in, it tries to raise the pressure in the system, but the bleed to the space above is still open, so it squirts out the top and into your face.  Keep pulling on the lever, and that bleed is covered up as the seals pass by.  At that point, it's a closed system, from the master cylinder's piston seals down to the slave.

So, pulling the lever in to the stop and walking away leaves you with a closed system.  No big deal.  Walking away for a few hours lets the tiny bubbles migrate up through the slightly thick fluid (thick compared to say, water), until they're resting against the piston seals.  When you then undo your lever and let it release, they cheerfully shoot up into the resevoir, and the next pull of the handle shoves fluid in, rather than air.

This is why when you bleed the system, you really only need to move the end of the lever an inch or so if that, but most people will persist in bringing it all the way to the bar, making themselves tired and cranky for no good reason.  It's really not a particularly difficult system to bleed, but it can be a bit twitchy to prime the master so that it moves fluid rather than air.  It's a little like trying to pour water into the top of a glass rather than starting at the bottom, a tiny fraction at a time.  I think people have difficulty with it because they make it a lot more work than it really needs to be and give up early because they are wasting most of their energy and not really getting anywhere with it.  I don't even open the bleed at the slave until I've gotten some headway made on getting the system mostly full of fluid, because the air is going to naturally want to go out the top, rather than shoving it out the bottom.  Once you've got the system working but still mushy, that's when it's time to open the bleed at the bottom and start shoving fluid through gently.  Brake fluid is slightly thick stuff and doesn't want to be forced through like water!

Well explained andyb. I have used this method on two occasions. Once for the clutch and once for the front brakes. Both times, much better lever feel was achieved by the next day. It must be said, however, that before tying the lever back, I had bled all the air out of the system by the usual process. I think that the tying method only evacuates a very small amount of air that normal bleeding may not shift.  I only recommended this in a previous post      because I have had first hand experience with it actually working.   Pete.