Bleeding brakes

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2 hours ago, bluey said:

Interesting.  I do wonder why the bubbles could not rise with the lever at rest though?  When the lever is out, the bubbles could travel all the way up to the reservoir could they not?

Holding the hydraulic brakes on...under pressure... for at least a overnight time will cause the tiny air bubbles to travel up to the highest point...usually the fluid reservoir in this case...and give a more firmer feel to the pedal/ lever. On bikes I’ve had with hydraulic brakes this method works every time. Fairly obviously the system will either have been bled prior to this or after use i.e. putting the bike away.?Bubbles can’t get to the reservoir if the lever is off due to there being no real pressure in the system, any residual pressure is not sufficient to create the effect.??

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1 hour ago, oni nou said:

Yes, its best for you not to do it.

 

1 hour ago, oni nou said:

Yes, its best for you not to do it.

No to what? Holding the brakes under pressure after bleeding will cause any tiny bubbles in the fluid to rise.?

[bluey]

20 hours ago, oni nou said:

If you search through my previous posts you will find this method discussed in some depth, there is great aversion to this method for some strange reason.

I don't have any aversion to the method.  I just have an inquisitive mind and don't yet understand why a bubble that is compressed and made smaller and less buoyant rises easier in a brake system.
As a diver I know that bigger bubbles rise faster and with more force (in that environment). 

I'll go and have a look at your previous posts.

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On 18/12/2017 at 7:44 PM, bluey said:

Interesting.  I do wonder why the bubbles could not rise with the lever at rest though?  When the lever is out, the bubbles could travel all the way up to the reservoir could they not?

You have to encourage them (the bubbles) to actually rise to the top otherwise they stay in the fluid lines. It’s a practice that has been employed for a long time in the bike trade. ?

[martym]

I too was skeptical about this procedure. But give it a try.  On my beta it decreased my front brake lever travel by at least 30%. You have nothing to loose and easy to do.

Now if I could only get the rear brake to operate more efficiently I would be happy. Ive done everything to improve its operation. Pads and bleeding. The rotor is slotted. I may try a solid one.  Its operation at best is either on or off. My old sherco has much better feel and a solid rotor. Ive rode a 4T and by far the best brakes over all on any bike. And it too has a solid rotor . Am I on to something?

Marty

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On 19/12/2017 at 7:27 PM, bluey said:

I don't have any aversion to the method.  I just have an inquisitive mind and don't yet understand why a bubble that is compressed and made smaller and less buoyant rises easier in a brake system.
As a diver I know that bigger bubbles rise faster and with more force (in that environment). 

I'll go and have a look at your previous posts.

Ah yes but also in the depths the air in your body compresses and can cause grief when you start to surface they expand. Because in a hydraulic brake system the air is being compressed the bubbles have more tendency to rise to the highest point or float if you will. Big bubble compressed down in size still has the same ability to float.

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On 29/12/2017 at 1:48 AM, martym said:

I too was skeptical about this procedure. But give it a try.  On my beta it decreased my front brake lever travel by at least 30%. You have nothing to loose and easy to do.

Now if I could only get the rear brake to operate more efficiently I would be happy. Ive done everything to improve its operation. Pads and bleeding. The rotor is slotted. I may try a solid one.  Its operation at best is either on or off. My old sherco has much better feel and a solid rotor. Ive rode a 4T and by far the best brakes over all on any bike. And it too has a solid rotor . Am I on to something?

Marty

You should try levering the pads back into the caliper using care, fill the gap between pad and disc then bleed brakes. Try the lever/pedal before removing packing pieces it should feel quite hard (steady girls). Now remove packing and try again, remember you are now pumping the pads back out to meet the disc. The fact that your disc has slots in it will not affect the lever/pedal feel.

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[carl ekblom]

Interesting. Thanks

[bluey]

On 7/25/2018 at 10:02 AM, section swept said:

Big bubble compressed down in size still has the same ability to float.

No it doesn't because a smaller bubble has a higher ratio of surface area to volume therefore it has more resistance to moving through a viscous fluid.

A larger bubble has a lower ratio of surface area to volume and can push through the fluid faster (effectively a better power to weight ratio).

I reckon in a glass of fizz, the last bubbles to remain stuck to the sides of the glass and not rise to the surface will be the smallest ones.

BTW I still accept if something works, it works.  Just don't understand why yet  but I enjoy these conversations cos I love learning stuff..

 

edit:  Just had a thought.  Maybe you are onto something with the diver, bends thing.

When a diver breaths at depth the gas is motabilized into the body at the normal bubble size.  When you ascend to less pressure the bubbles grow to a larger than normal size and they can not escape from the body tissue as easily.  Only when they are re compressed in a chamber can they exit.  Maybe the same with a hydraulic system somehow.

BTW air compresses to half it's volume at 1 bar or approx 15psi of pressure.

Edited July 27, 2018 by bluey