Bad Brake Line?

I have an 05 crf450 that sat for about 3 weeks while the engine was getting rebuilt. Since then, the rear brake has not worked properly.  There is plenty of resistance when pushing down but it will not even lock up the rear wheel.  So I bled it with my vacuum pump, but no improvement. I bled it manually but still no improvement. So I installed a new rebuild kit for my master cylinder (and bled it again), but still no improvement. My brake pads are next to new and look great. I can see the caliper push the pads against the rotor and plenty of resistance is felt in the lever. It will cause the bike to slow down eventually but it wont lock up the wheel. Any ideas? Ive heard of brake lines possibly swelling?

I've had air bubbles in two frount brake master cylinders that I was able to dislodge by very heating gently with a heat gun and snapping the lever many times to bump the bubble out.  Both had the same symptoms.  Not sure if thats your problem but its very easy to try and costs no money.  Unless you melt something with the heat gun.  I'm guessing I heated it upto maybe 120 degrees over 4 mins or so.  Whole process took about 10-15 mins to clear out the tiny bubbles and it worked perfectly.

Triple check there is no air bubbles and clean off your rotor and pads with some break cleaner.


I got wd-40 on my rear brake once and there was plenty of resistance but it wouldnt slow down

If you have normal pressure and feedback on the pedal, it's not a hydralic problem, it's a surface contact problem.

It's possible your pads and rotors are contaminated with oil.

You need to clean the rotor with spray brake cleaner and scotch brite, and the pads with brake cleaner and 80 grit sand paper.

Then you need to re-seat the pads to the rotor, by going down hill and applying varying amounts of pressure starting soft, for 4 sec at a time, until you eventually over 5 min get to full pressure.

That is called a 'cold seat' and will not glaze your pads again.

Thank you guys for the responses. I am out of town till the end of the week, but will try that when I get back. I'll let you know if it works. Thanks

Kranie, you need to write us a book!  call it "Dirtbikes...Shit I Know That Works"  absolutly no disrespect intended!

Yeah , Krannie has knowledge .. No question

I used his info to turn a stock (CRF450X ) into a decent trail weapon

Kranie, you need to write us a book!  call it "Dirtbikes...Shit I Know That Works"  absolutly no disrespect intended!

To answer the question, yes, you could have a bad line. When you put pressure on the pedal, check the line by feeling and see if its growing over a length of it. Ive replaced several OEM lines that have failed internally and balloon over a length that isnt horribly obvious to the eye.


Krannie has solid advice on reseating the pads though.

My 06 had a rear brake that go mushy.  I dicked around and replaced the pads, rotor (needed to be repalced anyway), rebuild master cyl, disassembled and cleaned caliper, greased pins, and bled the thing every which way imagineable.  Then I sped the $32 to get a steel braided line.  Now it's solid as a rock!  I think they just fatigue and die afer a while.

Thanks everyone. I took some scotchbrite to the pads and cleaned the rotor. works great now with no problems

Kranie, you need to write us a book!  call it "Dirtbikes...Shit I Know That Works"  absolutly no disrespect intended!


Ok, will you publish it?

I would have to read the manuscript first, but think of how much better the world would be with this literary work available.


I could proof read it if you like!

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