Front Brake Spongy

[effjayr]

OK so I have replaced the stock brake lines with stainless hoping it would cure the spongy feel. I have bled this thing 6 ways to Tuesday with every trick I can think of to get the supposed air out of the system. I see no evidence of air out either bleeder and it has sat for days now as well. The brake lever has always been that way since day one. Is it possible the master cylinder is root of the spongy feel? I can pull the lever all the way in if I squeeze hard. I have 2 other bikes -1 with rubber hoses still that I can't do that on. Any ideas?

 

[Ignacio]

You tried the trick of wrapping the brake lever with a bungie overnight in the fully squeezed position?

 

[Zorlac]

You tried the trick of wrapping the brake lever with a bungie overnight in the fully squeezed position?

A strip of Velcro works well for this too.

 

[effjayr]

You tried the trick of wrapping the brake lever with a bungie overnight in the fully squeezed position?

A strip of Velcro works well for this too.

Have not tried this method; not sure how applying long term pressure helps but I'm willing to try. Thanks- I'll give it a go.

 

[RadioHowie]

[not sure how applying long term pressure helps but I'm willing to try.

The theory is with the brake lever strapped tight and allowed to sit overnight (or longer), microbubbles in the brake lines that refused to vacate during a bleed session can migrate up the lines and are then able to pass through the master cylinder, which is now being held open by the strap, and wind up in the reservoir, where they can do no harm, instead of in the brake lines, which causes sponginess.

That's the theory. But I've heard proponents of this method on more than one motorcycle forum, so it must have merit.

 

[lonerider]

When I first got my '07, I had a problem with the front brake. When holding the lever in at a stop, it would loose pressure; the lever would slowly go to the grip. My local dealer (where I bought the bike) changed out the master cylinder assembly under warranty and that took care of the problem.

 

[Bustanut joker]

FUZZY BALLS!! with regards to the bunging the lever. Did that after I couldn't seem to get all the air out no matter what I did.

Left it for about a day an a half and 'twas all good.

I'd give that a go before spending your money on a master cylinder.

:jester:

 

[user 213]

Std or ABS?

Sometimes it's very difficult to get the air out of new brake lines w/o a pressure bleed. Vacuum bleeding is easy and usually effective, but do the brake lever bungie, (or velcro strap), then try bleeding again with only the master cylinder for pressure.

 

[Afast03nNJ]

The theory is with the brake lever strapped tight and allowed to sit overnight (or longer), microbubbles in the brake lines that refused to vacate during a bleed session can migrate up the lines and are then able to pass through the master cylinder, which is now being held open by the strap,

That theory is incorrect. When the m/c is activated it's closed to any return of fluid while the system is pressurized. It's only open when the brake is released, which is how your piston retracts (fluid travels back)

I would overhaul the system. Rebuild the calipers, bleed again. Usually when a m/c fails the bake pressure will be completely lost if you attempt to hold pressure over a period of time. Spongy brakes most always point to air or faulty calipers.

 

[effjayr]

Calipers were rebuilt with new seals since I was there anyways on disassembly. Not sure how a caliper would cause spongy feeling unless there is a mechanical integrity issue with the caliper body itself. Worth looking at for sure. I'll try the holding of the brake and let it sit. If the m/cyl is nfg then the lever should eventually go full travel I figure. The other thing I could do is take a syringe and inject clean fluid through the bleeders- careful that I don't put air into the system. Oh I forgot to mention it is is non-abs so pretty simple system. Thanks for all the suggestions!

Will advise outcome.

 

[RadioHowie]

The theory is with the brake lever strapped tight and allowed to sit overnight (or longer), microbubbles in the brake lines that refused to vacate during a bleed session can migrate up the lines and are then able to pass through the master cylinder, which is now being held open by the strap,

That theory is incorrect. When the m/c is activated it's closed to any return of fluid while the system is pressurized. It's only open when the brake is released, which is how your piston retracts (fluid travels back).

Okay, assuming you're right and I'm wrong, then why do so many report success with eliminating spongy brakes after doing the brake-lever-strap-boogie? What purpose does it serve that seems to work for so many, and where is the air in the system going, if not back into the m/c?

 

[effjayr]

The theory is with the brake lever strapped tight and allowed to sit overnight (or longer), microbubbles in the brake lines that refused to vacate during a bleed session can migrate up the lines and are then able to pass through the master cylinder, which is now being held open by the strap,

That theory is incorrect. When the m/c is activated it's closed to any return of fluid while the system is pressurized. It's only open when the brake is released, which is how your piston retracts (fluid travels back).

Okay, assuming you're right and I'm wrong, then why do so many report success with eliminating spongy brakes after doing the brake-lever-strap-boogie? What purpose does it serve that seems to work for so many, and where is the air in the system going, if not back into the m/c?

Im wondering if the pressure squeezes the bubbles such that they are more free (smaller) to migrate up to the m/c. Lever is clamped as we speak so we'll see. I'm also wondering if some road time with the fork motion may help if there is air. They're not so bad I can't ride it. Stay tuned for results later this weekend. Thanks to all.

 

[Fred W]

The theory is with the brake lever strapped tight and allowed to sit overnight (or longer), microbubbles in the brake lines that refused to vacate during a bleed session can migrate up the lines and are then able to pass through the master cylinder, which is now being held open by the strap,

That theory is incorrect. When the m/c is activated it's closed to any return of fluid while the system is pressurized. It's only open when the brake is released, which is how your piston retracts (fluid travels back).

Okay, assuming you're right and I'm wrong, then why do so many report success with eliminating spongy brakes after doing the brake-lever-strap-boogie? What purpose does it serve that seems to work for so many, and where is the air in the system going, if not back into the m/c?

Howie,

He is right. When you pull in the brake lever it pushes the piston into the master cylinder, which blocks off the reservoir from the brake line. The only time that the line is partially open to the reservoir is when the lever is all the way out.

But you are correct too. Tying the lever tight often works to purge stubborn air bubbles. Here's how it works:

When you have a bubble in the system its surface tension tends to make it clink to the inner surfaces of the plumbing. By pulling the brake lever in you are increasing the pressure in the line. The effect is to compress any air in the line before actually moving the brake pad at the other end, that's why it feels spongy. The compressed air is now much smaller in size (volume) but is still much lighter than the brake fluid, so is still very buoyant and will now be able to rise through the system due to its smaller contact with the hoses, etc.

So the little compressed bubble(s) rise to the shut master cylinder. Then when you release the lever in the morning they expand and are simultaneously drawn back up into the reservoir with the up-rush of decompressing fluid.

At least that is how I believe that it works.

[edit] effjayr beat me to it while I was typing. But prompted me to remember one more point. If you tap on the pressurized brake line with a screwdriver handle or something like that you can help the little bubbles gravitate up to the master.

 

[FJRBluesman]

Could this be it…??

When a new set of pads are put on the bike one pushes the pistons into the caliper to get the new pads on, usually the pistons are pushed in further then needed to make it easy to get the new pads in. If I understand disc brakes, the seal helps pull the pistons back from the rotor when the fluid pressure is released. As the brake pressure is applied the seal deforms slightly, once the pressure is released, it will return to its natural state, thus pulling the piston back. I tried to find a diagram of this and I could not locate it. It might have been on this forum, I can't remember.

The piston seal is now pushed in so to speak. As you get fluid pumped thru it again, the seals are stretched to the other extreme in it's grip on the piston. The seal now wants to pull the piston back further then it has, thus creating a spongy feel. Over time this should correct itself, but maybe not. Keeping the brake lever full on, as explained above, may help the seal give a bit so you won't have that added distance of pull back on the piston.

Just my 2 cents or total wackiness.

 

[Afast03nNJ]

When you have a bubble in the system its surface tension tends to make it clink to the inner surfaces of the plumbing. By pulling the brake lever in you are increasing the pressure in the line. The effect is to compress any air in the line before actually moving the brake pad at the other end, that's why it feels spongy. The compressed air is now much smaller in size (volume) but is still much lighter than the brake fluid, so is still very buoyant and will now be able to rise through the system due to its smaller contact with the hoses, etc.
So the little compressed bubble(s) rise to the shut master cylinder. Then when you release the lever in the morning they expand and are simultaneously drawn back up into the reservoir with the up-rush of decompressing fluid.

At least that is how I believe that it works.

That makes complete sense to me!

Thanks Fred

 

[effjayr]

OK so the brake is much better now after the pressure hold method with a strap. Still not as solid as I would like so I may try pushing fluid up from the bleeders to see if that does anything. Appreciate all the help- always good to learn new tech tips.

 

[Ignacio]

OK so the brake is much better now after the pressure hold method with a strap. Still not as solid as I would like so I may try pushing fluid up from the bleeders to see if that does anything. Appreciate all the help- always good to learn new tech tips.

You could have gotten a big bubble, but there might be more bubbles that consolidate and migrate with a good long ride...then try the strap trick again. Opening up the bleeder could introduce fresh air into the lines.

 

[TownsendsFJR1300]

I have found that when coming across a problem similar to this and using the above mentioned methods, it helps to turn the forks to the left, on the side stand to allow the bubbles to work all the way up to the master cylinder.

Also gently pulling the lever and quickly releasing the lever will sometimes help relieve the sticking bubbles...

Scott