Spongy front brake and temporary fix

[Rolavine]

My front brake gets spongy, it still works just takes a bit more lever. So I put a clamp on the brake when the bike is parked that holds it on overnight, and then for the next month or so the brake is fine, no sponge, grabs right away.

So, any idea what might be wrong causing this?

And any idea why this works?

If this has been covered I couldn't find it with search!

Thanks

 

[Braenen]

This is your bike's way of telling you that it is going to kill you when you least expect it.

Bleed your brakes.

 

[Geezer]

Normally a spongy brake would indicate air in the lines. Since you have an '03, you are probably overdue for a change of brake fluid anyway so I'd bleed the brakes thoroughly to get the air out and fresh fluid in.

 

[Ignacio]

And an '03 is old enough that the lines could be deteriorating. IIRC, manual calls replacement every 2 or 4 years. Check for splits, cracks, bulges, soft spots, abrasions, etc......especially those areas that may have exposure to the sun and/or road debris......and/or think about replacing with a stainless like Galfer. Brakes are SERIOUS stuff to not scrimp on.

 

[SkooterG]

I think everybody above has covered it. I need to know more info:

When was the last time the brakes were bled?

When was the last time the brake system was flushed?

If the answer to those questions is 4 years or more, than that's most likely your problem.

If you have bled/flushed the brakes within the last two years then most likely you have some other problem where air is being introduced into the system. Could be the age of the stock lines and their detioration, or a connection/fitting, or the at the bleeder.

Start with the simple stuff first, and then work from there.

 

[Rolavine]

Thanks for the advice, and I did you all the greatest service one guy can ever give another, I took it!

I did a bleed - fluid replacement today. The brakes are nice and non spongy now. I got some air out of the lines during the process. Hopefully it will stay that way.

But I am curious about why that technique of clamping the brake on for awhile helps. The only way that makes sense is that some air makes it up into the resovoir when the brakes are held on, but I don't see how that is possible. How could the air make it past the cups in the master cylinder with the brake on? Maybe it gets drawn up the top near the master cylinder and then ends up getting burped out when the lever is taken back to neutral?

 

[HaulinAshe]

(...)But I am curious about why that technique of clamping the brake on for awhile helps. The only way that makes sense is that some air makes it up into the resovoir when the brakes are held on, but I don't see how that is possible. How could the air make it past the cups in the master cylinder with the brake on? Maybe it gets drawn up the top near the master cylinder and then ends up getting burped out when the lever is taken back to neutral?

You got it. Gravity, then burping.

 

[James]

But I am curious about why that technique of clamping the brake on for awhile helps. The only way that makes sense is that some air makes it up into the resovoir when the brakes are held on, but I don't see how that is possible. How could the air make it past the cups in the master cylinder with the brake on? Maybe it gets drawn up the top near the master cylinder and then ends up getting burped out when the lever is taken back to neutral?

I would think you may have a very small leak/crack somewhere. When you clamped the brakes on you basically bled the lines. Must be very small, or you would have seen brake fluid somewhere in the morning. Could have even been a slightly loose/dirty bleeder. just a guess...

 

[Fred W]

(...)But I am curious about why that technique of clamping the brake on for awhile helps. The only way that makes sense is that some air makes it up into the resovoir when the brakes are held on, but I don't see how that is possible. How could the air make it past the cups in the master cylinder with the brake on? Maybe it gets drawn up the top near the master cylinder and then ends up getting burped out when the lever is taken back to neutral?

You got it. Gravity, then burping.

+1

The reason this works is the air bubble becomes compressed so it is physically smaller. It still has the same relative gravity (buoyancy) compared to the fluid so it gravitates up, but its smaller size means it has less surface area to stick to the inside walls of the tubing. You can speed the process up by tapping gently on the tubing with the lever compressed to help the little buggers find their way up top the top. Then releasing the lever burps them back into the reservoir. Repeat as needed.

My main concern is how the air is getting in there. Did you have the bars off for any farkling? How about drops? Either of those things are likely to let air into the lines. If nothing like that then I'd be really concerned about leakage somewhere in the system.

 

[TILAM]

I have my bars off at the moment to repair the ignition switch and install my Brodie Fix. They have been off for maybe 3 weeks so I guess i can expect to have air in the lines. Question is if I put the resevoirs high before I reinstall them will the air rise back up to the resvoirs? I guess I can bleed them when I have it all back to gether but I'm thinking what goes up (once) can go up again. It's been in the low teens lately and we have a couple of feet of snow so it will be a while before I'm riding again. No rush getting around to putting it back together, what with an unheated garage and all.

 

[Rolavine]

Thanks even more for the follow ups.

I didn't have the bars off with a possiblity of air getting in, I kept them upright.

I inspected the system for any signs of a leak, very carefully.

Since doing the bleeding the lever has gone a bit soft again, so something must be letting some air into the system.

I will check out all the possible ways that could happen.

I thought that Fred W's explaination was great, and it makes a lot of sense.