Front brake driving me nuts


17 replies to this topic
  • Supafreak_711

Posted January 25, 2007 - 08:55 PM

#1

My front brake is driving me nuts... especially since I just had a similar problem with the rear which kept me off the track for the majority of my X-mas break (my biggest opportunity to ride of the whole year... as summer will be very busy).

I have bled and bled and bled it but it still feels like there is air in there. The brake is just mushy. The pads should be good (I replaced the pads on the rear when I had a similar problem, and it didn’t do a thing). I have tried bleeding the brake, as well as forcing fluid into the bleeder valve up into the reservoir trying to get bubbles out of there. I have also taken the top of the brake line off and forced fluid through there as I tightened it back on there to keep air from getting in there.

When my rear brake had this problem I also rebuilt the master cylinder, which didn’t do anything either. It turned out there was a air-bubble that was right at the top of the brake line that just wouldn’t come out.

I don’t know what else to try? I have tried the zip-ty trick. Any other way of getting air out that I haven’t tried? Should I try completely changing the fluid? (maybe it got contaminated?)

Thanks alot, unfortunately I will get home tomorrow around 6pm to try and get my bike back up and going so I can ride before heading back to school.

  • flintlock28

Posted January 26, 2007 - 04:40 AM

#2

I've been down this same road....

One last thing if you haven't tried it. Take the cover off the Master Cylinder, remove the front caliper, and use a c-clamp to FULLY push in both caliper piston's. THis is an area that air likes to hide in. You're removing the Master cylinder cap to allow the air to go up into the master cylinder. Be careful as some fluid may ride over the top of the Master cylinder and spill.

Another tip that somone else posted...When you are bleeding the brake, As you squeeze the brake lever (with the bleed valve open), shut the bleeder valve, and let the brake lever SNAP back as quickly as possible. Don't let the lever slowly come back to it's resting position, just let it go as quickly as possible. The guy who posted this didn't know how it works, but it was a tip given to him that he said definately works.

  • Ruttmaker139

Posted January 26, 2007 - 04:49 AM

#3

I experienced the same problem on my sons RM-125. I ended up rebuilding the master cylinder which did not correct the problem. I ended up going to an auto parts store and purchased a brake bleeder system. It has a vacuum pump and pulls the fluid through the system. Worked great. Good luck

  • Reyndogg

Posted January 26, 2007 - 07:01 AM

#4

What lever is on there?

I had a MSR i used as a spare that caused that exact feeling. For some reason I decided to put a stock lever on and it was perfect again. Looking at them side by side, I couldn't really see a difference but there surely was a difference in the way they work. My ASV C5 is fine as well.

Good luck.

  • GunnerV

Posted January 26, 2007 - 07:29 AM

#5

I've been down this same road....
Another tip that somone else posted...When you are bleeding the brake, As you squeeze the brake lever (with the bleed valve open), shut the bleeder valve, and let the brake lever SNAP back as quickly as possible. Don't let the lever slowly come back to it's resting position, just let it go as quickly as possible. The guy who posted this didn't know how it works, but it was a tip given to him that he said definately works.


I just bled my brakes last night and noticed the same thing. Maybe the impact of the lever jars the bubbles loose?:ride:

  • Supafreak_711

Posted January 26, 2007 - 09:21 AM

#6

Thanks guys, its a stock lever. I'll try fully compressing the pistons tonight. I pushed them in with a screw driver, but I'll try the clamp (that will probably let me push it a bit further.

If anyone finds themselves with this problem with the rear brakes... loosen the bolt connecting the brake line to the master cylinder and back bleed them a bit. Worked better than the new pads and master cylinder I bought :smachpc:

Thanks again guys, hopefully I get it working tonight. I also have to put new fork oil in there as my seals have leaked enough to notice the difference in fluid level. I doubt that the pads got oil on them, just because the brake problem started before the seals started leaking. I do have a spare set of pads in the garage to try in case... but the pads on there probably have at least 50% left on them.

  • flintlock28

Posted January 26, 2007 - 12:32 PM

#7

Yeah, regarding the brake lever being snapped back....I'm assuming the air bubbles are dislodged more efficientlly??

I think Baron Von Beard was the one who posted this little trick.

  • ZéPovinho

Posted January 26, 2007 - 03:34 PM

#8

if it is not one of the CR type line, some air might stay on the upper curve above the caliper. make sure the air goes staight up the line.
also while doing the snapping thing, tilt the master from one side to another cause sommetimes some bubbles get stuck too on the lever side

  • buzzgrizz

Posted January 26, 2007 - 04:31 PM

#9

You can also just leave the cover off of the reservoir over night or for a day or two and most of the time the air bubbles will work their way to the top.

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  • flintlock28

Posted January 26, 2007 - 06:50 PM

#10

You can also just leave the cover off of the reservoir over night or for a day or two and most of the time the air bubbles will work their way to the top.


&%$#@!?

Bad advise!!!! Brake fluid is Hygroscopic, which means it will draw mositure out of the air like crazy. You never want to leave the cap off the brake fluid bottle, any more than absolutely needed. In fact, I believe Motul brake fluid either uses Nitrogen in the bottle to displace any air, or it's packed in a vacuum.

Water is a bad thing in the brake system, it causes corrosion, and also can boil over since it boils at 212 degrees.

In fact, if you leave the cap off of a bottle of brake fluid, on a Humid summer day, you should just throw out the whole bottle.

  • Drav

Posted January 26, 2007 - 07:48 PM

#11

Another tip that somone else posted...When you are bleeding the brake, As you squeeze the brake lever (with the bleed valve open), shut the bleeder valve, and let the brake lever SNAP back as quickly as possible. Don't let the lever slowly come back to it's resting position, just let it go as quickly as possible. The guy who posted this didn't know how it works, but it was a tip given to him that he said definately works.


Leaving the valve open when bleeding risks getting more air into the system than getting it out...

Easiest way is to open valve, let it run till it stops, close valve, pump the brake for a minute, open valve, let it bleed out, keeping the res full....takes longer but you dont risk getting air in the system from backpressure....never had mushy brakes with this method.

  • grayracer513

Posted January 26, 2007 - 09:18 PM

#12

Brake fluid is hygroscopic, but not to that extent. As long as it's not raining at the time you work on it, you'll be fineSince you're working with a mushy brake, and not the installation of a new line, it should be easy.

One thing to think about, does go back to the hygroscopic nature of brake fluid. IOf the brake feels OK until it gets hot, you could have water in the fluid, which generates steam when heated, like fluid that makes its own air bubbles.

If you don't leave the cap off, you'll work way too hard. First, with the cap off and the bars tilted so that the master cylinder is titled slightly down at the output end, pull the lever only through the first 3 mm of piston travel and watch what comes up out of the fill port (there's a little screen over it) as the piston moves. If it's air, keep doing this until the big bubbles stop.

Now place a pan under the caliper and open the bleeder. Fluid should begin to flow out of the bleeder, but even if it doesn't look like it, keep an eye on the fluid level in the master cylinder. As it starts to drop, add more to keep it from running down to less than half full. As fluid starts running out, let it go until new fluid shows at the bleeder, and keep going until you see no more air. Close it off and give the lever another couple of tweaks to see if any more air was rolled up to the top. Top it off and try it. It should be good.

  • Supafreak_711

Posted January 26, 2007 - 10:52 PM

#13

Thanks guys, after some work it doesnt seem as mushy now. I will try it out tomorrow and see how well it works (didnt want to try it on pavement today, because I would round by brand new tires...)

I also discovered a little bit of black film on the pads (assuming it was just dirt and junk in there) so I took just the outer layer of the pad off so the surface looks fresh (like when they were new). Cut down on the life of the pad a bit... but if it makes it work better thats fine. Also I read one of grey racers posts in another thread about heating up a pad to get and oil out. I got the pads hot, and they smelled like arse... but not burning oil (I guess thats a good thing)

Thanks again guys, hope I find it works when I give it a real test tomorrow.

  • jimbob69

Posted January 27, 2007 - 03:21 AM

#14

I gave up on my yamaha master cylinder, I had the same problem. I got a used M/C of a friend from a 92' KX250, brakes blead easily and ive never had another problem bleeding my brakes, always a nice firm feel at the lever.

  • flintlock28

Posted January 27, 2007 - 06:05 AM

#15

Supafreak,

One last thing....do the Zip-Ty trick on the lever overnight...it can sometimes make a big difference.

From all the info. I've gathered, the Yamaha Master Cylinder is slightly inferior to Nissin's Honda model. (Doesn't Honda own Nissin?)....and I've heard Doug Dubach has switched to using KTM Master Cylinder's.

  • flintlock28

Posted January 27, 2007 - 06:11 AM

#16

Leaving the valve open when bleeding risks getting more air into the system than getting it out...

Easiest way is to open valve, let it run till it stops, close valve, pump the brake for a minute, open valve, let it bleed out, keeping the res full....takes longer but you dont risk getting air in the system from backpressure....never had mushy brakes with this method.


Drav,

I wrote that a bit unclear....

What I meant was: Squeeze the brake lever, crack open the bleeder valve to allow fluid to run out (while keeping lever squeezed), tighten bleeder valve, Now quickly let go of the brake lever. Evidently letting the lever go quickly, helps in dislodging remaining bubbles

  • John407

Posted January 27, 2007 - 10:12 PM

#17

I gave up on my yamaha master cylinder, I had the same problem. I got a used M/C of a friend from a 92' KX250, brakes blead easily and ive never had another problem bleeding my brakes, always a nice firm feel at the lever.


That's odd, when I had '91 thru '97 Kawi's tha hot mod was to put a Yamaha M/C on. When I did it gave me a much firmer lever than the stock KX250.

  • PAdaytonaman

Posted January 30, 2007 - 07:00 AM

#18

Just a thought on this, because it happened on a Nissin radial mount on my streetbike and that was you may have air seeping back thorugh your bleed screw.

Be careful and try wrapping the top of the threads, obviously don't get tape near the fluid, but that firmed up my brake right away and trouble never came back.





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