Spongy front brake

[ofrdrcr]

Hi, I have a 09 yz 450 and had to change the front brake line and now can't get the lever to feel solid. I have tried everything to get it to bleed, vaccum bled, gravity, level tied off, regular bleeding process to no avail. I even rebuilt master cylinder, no change. The bike has a steel braided line with new pads, 270mm rotor. I even tried to put a different line on it. Any ideas? Caliper rebuild? HELP!!! Thanks

[Yamiryder]

What exactly does the lever feel like? Does it grab and let go, or is it just soft?

[Fabulous]

My 08 is like that as well. Changed the fluid, new pads and still the same?! Works well, but just feels spongy...

[Dirty Twin]

I used to have the same problem on a KTM 525 I used to own, and never did get it figured out, did all the same things you have done, and finally decided to just "ride" around it!, my gut say's the problem is in the caliper, either a "soft" seal at the piston, or the piston is "hanging up" slightly and not returning into the housing all the way, either way try this, it temporarily "solves" the soft lever, kinda like adding oil "cures" an oil leak!

Get you a zip tie, pull the front brake lever on as far as you can, ziptie around the handle bar and lever to keep it as ON as possible, let the bike sit over night, now here is the important part, take off the zip tie before you go riding!!, the brake will have firm feel for your ride, wash dry and repeat before each ride this summer, then this winter, when you have more time on your hands, pull that whole brake ALL apart, it could be the diaphragm in the master, but I am guessing that it is at the "other" end of the system, clean, replace and rebuild the whole system, or ask Santa for an "upgraded" aftermarket brake, but then you would have to be "good" for the rest of the year!

[davidhasselhoff]

Try bleeding it at the upper banjo bolt. I couldn't get a good lever feel in my '06 after putting on a SS line until I did this, even after running half a bottle of brake fluid through the system.

You might also try using a zip-tie to keep the lever compressed for a few hours before bleeding. This seems to help too.

[Mr. Neutron]

Some of the KTMs would have problems with their brakes occasionally, after a fall or something similar, that somehow, let air into the system. Changing pads, fluid & such would allow it to happen also, sometimes. One guy on the KTM website had pretty good luck "reverse bleeding" his brakes (the credit goes to ktmtalk member "JEB"):

The way I like to bleed brakes is reverse bleeding. I get a large syringe (6"x3/4" or so)

from a farm supply store and a foot or so of small rubber hose. Ziptie the tube to the

end of syringe. Push the caliper against the rotor to bottom out the caliper piston. If

you have the wheel off, clamp the pads against the piston with a C clamp to hold the

piston compressed. I really recommend the C clamp method, BTW. This has yielded me the

most consistent bleeds.

Fill the syringe up with brake fluid. I like Motul 5.1 but 4.0 and 3.0 will work as well.

Slowly squeeze the plunger as you attach the hose to the closed bleeder to minimize air

bubbles. A small ziptie around the hose/bleeder junction helps, too. Unbolt the resevoir

and let it hang over a pan.

Make sure the MC plunger is not engaging the piston as that will make it hard to force

the fluid up the line. Open the bleeder and start squeezing. You may have to use a fair

amount of force but don't overdo it. When the syringe is about 80% empty, tip the

resevoir up and push the rest of the fluid in. Tighten the bleeder while still pushing.

Take the ziptie off, top off the resevoir, and pump up the brakes. Now bleed it

traditionally for one or two times just to make sure you didn't leave an air bubble in

the caliper. Do the same after you remove the C clamp, if you used one.

I seem to faintly recall a way some guys would bleed their "hard -to-get-the-air-out" fronts by removing the caliper, putting it up on a bench, removing the master cylinder/lever from the bars, and with the m/c/lever lower than the caliper, bleeding them somehow that way. It always seemed too much trouble to me, and especially when considering that conventional bleeding worked well enough for myself. Some of the KTM guys even went as far as putting Honda/Nissin m/c setup on their bikes to fix this problem of tough bleeding/air getting into the system.....

Hope maybe this might help some.....

Jimmie

Added in EDIT:

Ofrdrcr, please let us know what you think about your front brake mods, after you get the thing bled good. I really miss the great front brake my KaTooM had, and have considered a braided steel line & different pads, at a minimum....

Edited July 22, 2011 by Diesel Goober

[ofrdrcr]

I have tried the hanging method with the whole system off bike. No luck. I also tried the banjo bolt method. The brakes feel spongy when you grab the lever. I can pull the lever all the way to bars with one finger. The bike has decent braking power, not as much when it was new, and it has a 270 rotor on it now. I have compressed the pads into the caliper to force air out. No change.

[tech24]

Have you ridden it yet? Try ridding to burnish new pads in, depending on pad compound it may firm up.

[ofrdrcr]

Rode it for a half hour in the woods next to the house. Probably didn't get it hot like at the track. Would the caliper cause this problem? Going to try the reverse bleeding method. I have hung the brake system in every position possible and tied the lever off numerous times. ARGH!!!!!

[ofrdrcr]

Just did the reverse bleed to no avail. Also regular bled it after that. Ordered a caliper rebuild kit today. Keeping fingers crossed. Will get it next week. Any more ideas??

[tech24]

anything is possible. 30 min should have made a difference if feel if it was going too.

What pads did you get? Did you get any grease or brake fluid on pads or rotors?

[the_artist]

Gee! feels like déja-vu... I just installed a new 270 rotor with new pads and a SS line, vacuum bled the hell out of the thing and used motul 5.1 fluid, I did the bedding-in process and all and ... Still got that limpy feeling at the lever and hardly a 10% gain in stopping power. I read all those stories of guys doing stoppies at the flick of a finger. Well, when I break with one finger, the other three act as stoppers for the lever !! Nedless to say I'm anxiously waiting to see if a caliper rebuilt kit cures your woes, cause I'm hesitating between that or switching to a Honda Master cylinder.

[grayracer513]

There are non-hydraulic causes for this that no one has mentioned. The caliper must be square with the surface of the rotor, or part of the lever travel will be used to get it twisted into position. Watch the caliper as the brake is applied. If it twists, turns, rolls, flexes, or whatever to a significant degree, start with a fresh set of pads and see if that fixes it. If it still squirms, shim, bend, or file something until it doesn't anymore.

[the_artist]

Makes sense Gray, thanks for the pointers.

[Mr. Neutron]

There are non-hydraulic causes for this that no one has mentioned. The caliper must be square with the surface of the rotor, or part of the lever travel will be used to get it twisted into position. Watch the caliper as the brake is applied. If it twists, turns, rolls, flexes, or whatever to a significant degree, start with a fresh set of pads and see if that fixes it. If it still squirms, shim, bend, or file something until it doesn't anymore.

This is a good point..... If the pins get grooved that the caliper is supposed to slide on, what Grayracer513 described will happen. A lot of folks neglect to replace those pins.....

Jimmie

[ofrdrcr]

Argh, rebuilt caliper and bled. No change!!!! Took apart master cylinder again and cleaned and put back together, bled, no change. I am wondering about the alignment of the new large rotor and mounting bracket. I have read that if the pads are too far out in the bore that will cause spongy feel. Any ideas? Honda master cylinder? Ha Ha

[ofrdrcr]

Rebuilt caliper, no change. Took apart master cylinder and cleaned and inspected again. Put it all back together, same spongy feel. I can pull handle all the way to bars with 2 fingers. What next? I really think this bike was built on a monday or friday!!!!!! Any ideas?? HELP!!!!!

[tech24]

Maybe put to old rotor and pads back on and see if there is a change?

[ofrdrcr]

The problem has been around before the large rotor. It has very little runout on it so that isn't the problem. Will have a chance to go riding this weekend, so will see how it acts when hot. Maybe something will change. Yeah ha ha. Will keep posted. Any ideas on a honda cylinder? What year?

[eazrider]

Rebuilt caliper, no change. Took apart master cylinder and cleaned and inspected again. Put it all back together, same spongy feel. I can pull handle all the way to bars with 2 fingers. What next? I really think this bike was built on a monday or friday!!!!!! Any ideas?? HELP!!!!!

If you're pulling the lever all the way to the bar with 2 fingers, you've still got air somewhere in the system. Sounds like you're doing all the right things to get all the air out, but not being successful. Keep working it 'till you get the air out, I know sounds simple, and really, it is.....just not easy....