Inconsistent Squishy Brakes

[nodakgus]

I just took my 2007 ZX-6R out of my house today after hibernating in my dining room the last 4.5 months. Started right up (though it was on a battery tender). My front brake was soft but it pumped up firm right away. Then I drove it down the street and when I applied the front brake it again was very soft but...it pumped up firm right away. This was a consistent pattern - go soft but pump right up firm. The resevoir is full of brake fluid.

I am at a loss for an explanation on this one :dunno: ...any mechanical slueths out there who can pinpoint this? opcorn: By the way, last November when it was last ridden no such issue existed.

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[darth nater]

Maybe just some air bubbles in the lines from sitting over the winter. My guess would be to bleed them a little with some fresh fluid.

I am not mechanic, just what came to mind first.

 

[HondaGalToo]

Agree, when was the last time the fluid was changed? Try bleeding first, that's the simplest thing to rule out.

 

[betarace]

A tip to remove "microbubbles" is to pump up the brake lever to rock hard and zip tie the handle back to the grip as hard as you can. Leave it overnight and repeat. The pressure in the system helps the bubbles float to the top and past the brake piston.

Note: this assumes small bubbles and a deent bleed job and fresh fluid to start.

 

[stkr]

I Agree - Bleeding

If that doesn't solve it, then you may want to try cleaning the calipers, and checking for a slightly bent rotor. If I a rotor is bent, then as it rotates, it can push the pads back, which pushes the pistons back in the calipers. When you go to brake, the first couple of pulls on the brake lever will only be moving the pistons/pads back out until the pads finally start gripping the rotors.

Note: If you didn't have problems last year, then I doubt your rotors are bent. Try bleeding first. Was anything dropped against the bike in the dining room? Kids running around it?

Good Luck

 

[Matt]

bent rotor.

pump it up, roll the bike exactly one wheel revolution. if it's soft again, it's a bent rotor.

that method doesn't work on rotors that only have a slight bend, but it sounds just like something someone had this weekend at the track.

 

[bigkaley]

Also, FYI, the "zip-tie" method of holding the brake lever for the theory of keeping the brake line open to allow the bubbles to bleed back up to the master cylinder does not work. The master cylinder piston has 2 seals on it, and when the zip-tie is used on the brake lever, it does not keep the master cylinder piston in an "open" position which would allow the bubbles to return. For example, on a 1 piece master cylinder/ reservoir assembly (the reservoir is not seperate from the master cylinder) there are 2 holes in the bottom of the reservoir, one is the fluid "in" hole and is easily seen, the other is very small and is the "return" hole. When you pull the lever, you close the return hole with one piston seal and the other piston seal pushes or "compresses" fluid. Since the "return" hole is closed, the fluid is compressed down the lines and pushes the caliper pistons out. When you release the lever, you "open" the return hole again, and the fluid can relieve the pressure back into the reservoir.

Clear as mud???:notsure:

 

[betarace]

Sorry Kaley, I'm not saying you should do it instead of changing the fluid, I'm saying it works. I change my fluid regularly, and that will make the most difference of anything. However, once I put on a new hose and couldn't get it to bleed no matter what I did. I finally gave up and decided to try the zip-tie method. Came back, cut the tie and the brakes were nice and firm.

Walk through the pits at a pro race and you will find a few factory bikes with zip-ties on the front brake. It works in a similar way that tapping the line with a screwdriver does. It loosens bubbles that are clinging to the side of the hose and allows them to rise to the piston in the master cylinder. As soon as you release the brakes the bubble is set free. I've done it on over 15 bikes and have never had any issues with it, it just works.

 

[bigkaley]

Eh....what do I know...

 

[Landshark]

I don't know about the air not getting back into the res. I think the pressure causes the air to compress making the bubble smaller and reducing the surface tension. That lets the bubbles flow rather than stick to the side. The air then rises to the top and into the master. If you tie the lever back before travel the vibrations help this upward flow. From there you can bleed the air out more easily than trying to make the bubble go down and out the calipers.

I like to use a clear hose on the master cylinder bleeder. This way you can see the air and not pump out too much fluid.

 

[Joe Vital]

letting the system alone for a period of time will also allow the bubbles to rise to the top. even small ones. it is likely that when folks let the bike sit over night with the lever pulled in the bubbles move up on their own. zip tying does nothing, unless you want to use it as a reminder to leave the bike alone for a while.
what do you do during the time you are letting the bike sit? go to auto-zone, sears, or harbor freight and get a brake bleeder thingy like mitey-vac, for example any one of these: http://www.thefind.com/cars/info-brake-bleed-pump

as tom explained, there is no mechanical way for the bubles to return with the lever pulled in.

the problem the OP described sounds exactly like a warped rotor, as has already been stated. if it turns out to not be a warped rotor, i would really like to know what the problem was.

 

[bigkaley]

Thanks Joe. I was about to call Fred at Yoyodyne and Britt Lynn (Matt Lynn's father who may have a little experience with race bike setup/ prep) and tell them they were wrong.... "The zip-tie method works!!" "All hail the 'Golden Zip-Tie' " :doh:

http://forums.13x.com/showpost.php?p=2453912&postcount=13

http://forums.13x.com/showpost.php?p=2453967&postcount=15

http://forums.13x.com/showpost.php?p=2455244&postcount=20

 

[sobottka]

the zip tie thing does work but rather than wait several hours for the bubbles to rise i arrange my bleeder hose in a vertical position above the bleeder valve. bleeed as normal untill the hose fills with about 2" of fluid then leave the bleeder valve open and pump a bunch of fluid through. since my bleeder hose is full of fluid, no air gets sucked back in when i leave the valve open. with all the fluid moving through the system comes the tiny bubbles with no overnight wait. i do this procedure on all bleeder valves but the master cylinder is the critical one
also brake pads that wear uneven (front to back, not left pad vs. right pad) will make your brakes soft as well

 

[Joe Vital]

tom i got a motive products power bleeder. it has saved me many zip-ties and a lot of time.
i have cobbled together some adapters for various master cylinders. it work great, very little mess.
website:http://www.motiveproducts.com/

i just noticed someone suggested they push the fluid up from the caliper to the m/c. i won't do this. pushing all that dirty fluid back up through the m/c seems counter intuitive. (if i mis-read forgive me.)

 

[sobottka]

Joe Vital;183163 wrote: tom i got a motive products power bleeder. it has saved me many zip-ties and a lot of time.
i have cobbled together some adapters for various master cylinders. it work great, very little mess.
website:http://www.motiveproducts.com/

i just noticed someone suggested they push the fluid up from the caliper to the m/c. i won't do this. pushing all that dirty fluid back up through the m/c seems counter intuitive. (if i mis-read forgive me.)

how do you push fluid from the caliper to the m/c? when i bleed it goes the other way ???




edit- i better also add that my above instructions are for hand bleeding not with the use of a vac/pump. to me, those things just make a simple job more complicated

 

[eE jeremy]

I agree that zip tying the lever back over night makes a huge difference, I do it every time I bleed any of my bikes brakes. Don't know why it works, just know it makes a big difference in lever feel.

 

[Mikey75702]

Joe Vital;183163 wrote:
i just noticed someone suggested they push the fluid up from the caliper to the m/c. i won't do this. pushing all that dirty fluid back up through the m/c seems counter intuitive. (if i mis-read forgive me.)

For a system that has a bit of fluid in it, it does seem crazy... but works pretty well if you just rebuilt the calipers and they are empty.


sobottka;183173 wrote: how do you push fluid from the caliper to the m/c? when i bleed it goes the other way ???




edit- i better also add that my above instructions are for hand bleeding not with the use of a vac/pump. to me, those things just make a simple job more complicated

The vac pump is awesome. I can bleed car brakes by myself in like 20 mins. The bike is fairly easy with the method you use, but the vacuum blender kit is just as easy.

 

[Gorecki]

Mikey75702;183200 wrote: The vac pump is awesome. I can bleed car brakes by myself in like 20 mins. The bike is fairly easy with the method you use, but the vacuum blender kit is just as easy.

:agree: UBER Easy!!!

 

[Matt]

i still say bent rotor in this case.

squishy without getting them hot... pump up, move the bike and they're squishy again... bent rotor.


i'm not an expert, but i don't believe the zip tie method works for the reasons most think it does. yes, it firms up your brakes but it isn't a FIX.

what do i know.. i can't even get my brakes how i want them on this new bike.

 

[HondaGalToo]

Joe Vital;183163 wrote:
i just noticed someone suggested they push the fluid up from the caliper to the m/c. i won't do this. pushing all that dirty fluid back up through the m/c seems counter intuitive. (if i mis-read forgive me.)

I've read that suggestion on various forums but never tried it. Hadn't thought about the fact that you're pushing dirty fluid up, hadn't thought about the fact that it does get dirty, but as it gets used, that makes sense. Crossing that "technique" off my list of things to try. Actually, since I have speedbleeders, it wouldn't work anyway.

I use a Mityvac if I'm priming dry lines. Otherwise, it's good old fashioned manual bleeding. I generally like speedbleeders, they help make it an easier job. Have had them leak around the threads as they get used, but they sell the red stuff to reapply to the threads, so I'm trying them again.

I've also heard about the zip tie the lever thing on many forums. Tried it a couple of times and noticed no difference. What works is just bleed, bleed, and bleed some more.