Front brakes driving me nuts

[brains]

My front brakes work well, I can even do an endo if needed, but they feel spongy when pulling the lever. Most front brakes will lock up at a point when being pulled, my don't.

First I tried a complete master kit, no difference. Then I tried a new banjo bolt thinking that maybe the light switch inside was not holding pressure, no difference.

The only thing left is the braided hose, but I find that hard to believe and is an expensive experiment.

Any ideas?

[blitz11]

1. How is your back brake?

2. If you suspect flexible hose, lightly sqeeze the rear brake hose, and depress the brake pedal. Sense the radial expansion (or measure it with a caliper by comparing the OD with the brake off vs. with the brake on). Then, do the same with the front brake line, and compare the two. if the front hose expands more, you might have weak brake hose.

3. If you're creative, you can build yourself a pressure sensor by getting a banjo bolt, a crush washer stack, and a schrader valve, and a tire pressure gage (cheap). drill/tap the banjo bolt for a schrader valve, use your washer stack to deadhead the banjo (stack washers to block fluid from escaping), and measure the pressure you can generate with the M/C. You can also compare this to a buddy's bike, or your rear brake.

If your pressure is low, then you might have a bad MC (if the cylinder walls are scored or pitted, fluid will leak past, resulting in low pressure).

Nothing beats a measurement.

[brains]

I tried an old trick that seems to have fixed the problem, it's not 100% but a lot better.

I tied a rag around the lever holding it in all night, as to let any air out that may be trapped somewhere that normal bleeding could'nt get rid of.

I'll see how it go's.

[darren]

I bleed my front brake initially by filling the reservoir leaving the cap off and slowly pumping the lever, normally you will see the air bubbles coming up from the master cylinder. I then continue bleeding on the caliper bleed nipple untill all the air is out of the caliper then leave for a couple of hours with the reservoir cap off, also tap the pipe to move the air up the pipe, pump a few more times on the lever again watching if any air comes up from the bottom of the master cyl.

[Eric K]

After struggling with the same issue you describe, here is what I found to be most effective at reducing front brake sponginess...

1) Take off the front master cylinder cover.
2) Take a screwdriver and push the front brake pad, which in turn pushes the brake caliper cylinder back. Push it in as far as you can.
3) Make sure any air bubbles under the baffle in the master cylinder are out of the fluid - light tapping works.
4) Repeatedly pull and release the brake lever at a moderate pace until the pads are fully seated again.

[brains]

Well it didn't last long, they are back to spongy again, will try all the tips, thanks

[darren]

There is another way, Back bleeding.

Remove resevoir cover and rubber,
Clean an oil can out, fill with brake fluid, Connect a clear pipe onto the spout of the oil can, pump oil can holding the pipe upwards to purge the air out of the pipe, then connect the pipe to the bleed nipple on the brake caliper, open the bleed nipple and pump the oil can slowly. The reservoir should fill pushing all the air out, once happy the air is out then remove the pipe and bleed on the nipple for a few pumps untill the reservoir level is correct,

try the brake.

[brains]

Thanks Darren, I have used that before but with a syringe.

One thing that I must mention here that I haven't see posted is to check that the lever and lever adjustments are out enough to allow the plunger to come all the way out before the lever starts to push it back in. This can make a huge difference, I found out the hard way with a mates bike.

[brains]

Found it!

At last, I found the problem. I striped another GG and then changed over one part at a time, until the entire front brake assembly was changed over. It didn't feel any better, then Murphy kicked in.

As I was pumping the lever I rotated the bars over too the other side past straight (if the bike was going straight forward) and big bubbles came up. For some reason I was always bleeding the brakes with the bars over to the right, air was being trapped somewhere. All sorted.

Mods it may be a plan to make this sticky as it may save someone a huge headache.

[jefgil123]

I know! I have in the past - "back bled" with syringe, foreward bled, and
still had sponginess...there must be air in the line anyways !

I have read of people taking the master cylinder off and hanging it so the
line is vertical, and tapping all along everything, and getting the tiny
bubbles to rise.