Front brake problems



23 replies to this topic
  • MXH

Posted September 01, 2002 - 07:14 AM

#1

Have noticed over the last few months that my '00 WR front brake is getting more and more spongy with more travel. Just ridden an enduro today which was very fast (therefore lots of braking) and the lever was coming back to the bars. I'm not losing fluid, so it must be the standard brake line expanding - mustn't it?

Anyone had the same problem? I assume the solution is to get a braided steel hose, but just want to check I'm not overlooking anything.

Cheers

Mike

  • Dan_Lorenze

Posted September 01, 2002 - 07:21 AM

#2

MXH, This is a common problem. I would guess that you don't have a front disc guard? This has happend to me too. I believe that your rotor is bent just a little (from an impact). As the bent rotor turns it gradually expands the brake pads so that they have a long way to travel, so instead of just "tapping" the lever you probably have to "pump" it a few times to engauge. My advise to you is to get an adjustable wrench and slide it on to the rotor where it is bent and try to straighten it, be careful not to really torque down on it too much. If worse comes to worse you could always get a new rotor. I really can't imagine it being anything else other than this. Good luck and let us know how it turns (sorry for the pun) out. :)

Cheers,

Dan

[ September 01, 2002, 10:22 AM: Message edited by: Dan Lorenze ]

  • MXH

Posted September 01, 2002 - 08:51 AM

#3

Dan,

Thanks for the response, but this isn't the problem in my case. If the disk rotor was warped, you would expect that pumping of the lever would firm it back up again - only the rotation of the disk would push the pads back. This doesn't happen in my case - the lever comes back to the bars even after pumping it a few times.

It almost feels like there's air in the system, but I've bled it through a few times but to no avail.

Any other ideas?

Mike

  • MN_Kevin

Posted September 01, 2002 - 08:56 AM

#4

Definitely could be the rotor!

Also,

I would also bleed your brakes>> both at the caliper and your reservoir (master cylinder).

I would recommend a stainless steel line, w/ fresh brake fluid (NOT DOT 5!!!!!!!!! :D ).

:) You should change your fluid ABSOLUTE MINIMUM ONCE/Year >> actually every 3 months or so. Brake fluid sucks up water like there is no tomorrow!! :D

If you want to go the CR style brake routing kit, the problem is your headlight. The YZF's brake line goes diagnolly across the front # plate. Your headlight has an issue w/ this.

I went w/ the replacement, WR routing, SS line. I could not be happier, unless I slapped on a Honda Master Cylinder.

  • Mark_Cantrell

Posted September 01, 2002 - 11:18 AM

#5

MXH,

Yeah, but that's not the way it works. Do this as a test. Go position a flatblade screwdriver between the front pad and the rotor. Gently, not scratching or dinging the rotor, spread the pad about 3/8". Your theory would have a 'firm' lever. Try it. The lever will be pure mush and push the pad in 1/8" or so. The next pull will do the same thing. The 3rd or 4th pull will get the pad back in range of the rotor and firm up.

This same thing, on a smaller scale (hopefully) is happening with a slightly dinged or warped rotor. I agree with Mr. Lorenze that is the most likely problem. After that, low fluid in the reservoir, leaking pistons, expanding brake line, etc. You can tell if the rotor is warped by raising the front wheel and spinning it. If it is warped or dinged, it will have visible side to side runout.

Good luck,
mwc

  • Dan_Lorenze

Posted September 01, 2002 - 02:18 PM

#6

[ September 01, 2002, 05:20 PM: Message edited by: Dan Lorenze ]

  • Dan_Lorenze

Posted September 01, 2002 - 02:24 PM

#7

Originally posted by MXH:
the lever comes back to the bars even after pumping it a few times.

Any other ideas?

Mike

MXH, Are you totally sure that the wheel wasn't spinning at all??? Put your bike on a stand and try it again with the wheel locked to your fork with a tie-down so it won't move. If you've completely bled the system I can't imagine what else it could be... Get back to us.

  • Dean400

Posted September 01, 2002 - 08:01 PM

#8

I have the same problem with my 98 WR400. The lever is so spongey it almost hits the handlebars. I even have a Fastline braided line. I have done a search on brakes, and tried these things. I bled the brakes from the bleeder screw and both banjo bolts. I used a syringe to inject new fluid in from the bleeder screw. And, I used a zip tie to hold pressure on the lever overnight. None of these things worked for me, and now I am really confused. :)

  • banffboy

Posted September 02, 2002 - 05:40 AM

#9

I've just come up with the same problem in the last couple of rides. I've done and checked everything above. I was told that it could be an internal seal that the brake fluid is pushing past. I have no leaks anywhere. So maybe it's time for a rebuild? :)

  • YAMAKAZE

Posted September 02, 2002 - 06:45 AM

#10

COMPLETEY....and...PROPERLY....Flush and Bleed your system. If you have one or have access to one, use a Mighty Vac to ensure that ALL Air has been removed from the system.

When brake fluid gets OLD and burned from constant heating and cooling it looses it's viscosity...therefore giving a spongy pedal or lever. Brake fluid should be flushed often...The harder you ride/race the more often it should be changed.....I change mine when I change my oil...Brake fluid is cheap (DOT4 High Temp) and fast with a mighty vac (5 minutes).

Bonzai :)

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • sabin

Posted September 02, 2002 - 10:43 AM

#11

And what is the isue for not using dot 5.1?

  • MN_Kevin

Posted September 02, 2002 - 11:42 AM

#12

From what I recall, DOT 5 (5.1?) is COMPLETELY INCOMPATABLE w/ ANY other brake fluids. You have to do a THOROUGH flushing of your ENTIRE system prior to calling it complete.

I thought there were other reasons as well...but cannot recall. I do know, for all the trouble, it was not even worth considering.

I think the DOT 5 fluids were for EXTREME braking temperatures, NOT something any motocross/race bike would even come close to seeing.

Anyone feel free to correct me if I am wrong!

  • sabin

Posted September 02, 2002 - 11:59 AM

#13

Check out this:
http://www.motocross...tips.asp?id=106

  • MN_Kevin

Posted September 02, 2002 - 11:29 PM

#14

Sabin,
Thanks for the link!!! :)

DOT 5.1 DOES sound like the way to go!!

GREAT JOB!!!!@

(I myself use Castrol Racing Dot 4)

  • YAMAKAZE

Posted September 03, 2002 - 02:12 AM

#15

Now I wish I had held onto a quart of 5.1 that I recently purchased ($35.00. I didn't use it because I was advised by a respected mechanic that I would in fact have to completely drain,and dry my system before flushing. But, according to this article, I could have just completely flushed the system with the 5.1 and been done with it.

Maybe I'll purchase another quart of it next payday.

Thanks Sabin,

Bonzai :)

  • MXH

Posted September 03, 2002 - 03:49 AM

#16

Mark, I agree with your screwdriver test - but the bike is stationary (ie the front disk is not spinning) and I can pump the front brake 10, 50, 100 times and it does not firm up. If a bent rotor was causing the problem, would you not expect it to firm up in this test??

Therefore it's something else - I have tried bleeding the whole system through with new brake fluid but it's still the same. Suppose I'll just
have to get a braided hose and try that.

Mike

  • Mark_Cantrell

Posted September 03, 2002 - 01:21 PM

#17

MXH,

I'm not sure I understood your first sentence. I think you meant that if the wheel is still and you use a screwdriver the lever will firm up after a few pulls. But on your bike, when riding, the lever never firms up no matter how many times you pull it.

If that is what you meant, a warped rotor would not firm up the lever but instead push enough fluid back into the master cylinder's reservoir while the lever was released that pulling it would not reseat the pads. The lever would always be mush.

This is a long distance diagnosis. If you want to be sure, put your bike on a stand with the front wheel off the ground. Pump the lever a few times until the brake is firm, normal feeling. Release the lever, spin the front wheel rapidly for a few seconds. Now see if it the lever is still firm. If mushy or requires more than one pull, the warped rotor caused it.

(OK, long shot but a leak could also cause it, the double blind test would be to firm up the lever, release it, and let it sit the same amount of time you rotated before. If it was mushy after turning but not after sitting the same amount of time, it really is the rotor.)

You will probably also be able to see the side to side motion (a very little is acceptable), the runout spec is in the manual.

Good luck,
mwc

  • MX_Tuner

Posted September 03, 2002 - 02:43 PM

#18

Apparently some are confusing DOT 5 and DOT 5.1. There is a big difference. DOT 5 is silicone based fluid and can not be mixed with any other type fluid. DOT 5.1 is completely compatible with the DOT 3 and DOT 4 fluids. Motul sells DOT 5.1 and is a very good fluid. Brake fluid is not all the same, even as far as DOT numbers go. I get a noticeably better feeling lever with Motul than any other high performace fluid.

  • MXH

Posted September 03, 2002 - 09:50 PM

#19

Mark,

I was saying that I agree with the theory of your screwdriver test.

BUT the problem is that I cannot firm up the lever no matter how many times i pump it. The bike is stationary and I am pumping the lever but it does not firm up. I am not spinning the front wheel at all - that's why I'm saying it can't be a bent rotor.

Mike

  • MN_Kevin

Posted September 04, 2002 - 01:53 AM

#20

Maybe an rebuild of your Master Cylinder is in your future?

I know Moose offers rebuild kits for Quads...




 
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