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No back brakes???
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Posted by: dave2005---------------------
I have a 2003 Honda CRF450R. One day while riding, my back brakes just went out on me (no stopping at all and I could press the petal all the way down). I took off my brake pads and they were completely worn down. So I picked up some new pads and replaced them. Well, I still have no back brakes, the brake fluid levels are all good. Does anyone have any ideas?
Thanks
Dave
Posted by: dirt bike dave---------------------
Sounds like you boiled the fluid and still have bubbles in the system. When you are pressing the pedal, you are just compressing the bubbles, and not moving the brake pads.
As fluid ages, it gets contaminated with moisture and debris, lowering the boiling temp.
Replace your fluid and bleed the air out of the system.
For fluid, I've had excellent success with Motul 600. It has a higher boiling temp than most.
Posted by: dave2005---------------------
hey dave thanks a ton man. I will give it a shot.
Dave
Posted by: dirt bike dave---------------------
I drag my back brake alot, and I'm a big fan of the the Motul 600 fluid. In my experience, it is much more resistant to boiling than other fluids.
BTW, if your brake pedal is set too high, it is easy to drag the brake, which will wear out the pads and generate heat.
Posted by: whenfoxforks-ruled---------------------
Power bleeding and stainless lines. 2 best things for older bikes with brake issues. If you have been watching the level drop, as the pads wear, and putting more oil in. Not taking the reservoir cap off when you push the piston all the way back in, will result in blowing a seal somewhere. Mushy brakes can be air or a weak hose.
Posted by: dave2005---------------------
Well, I have went through an $8 bottle of brake fluid trying to bleed these god forsaken brakes and still nothing. I am doing all of the steps right, but am still getting small bubbles of air coming out. As soon as I start making progress and the pedal starts to firm up some what, I get a huge air bubble to come out, and I am back to square one with no pedal at all.
Here are my steps.
1. pump pedal 5 times and hold
2. crack bleeder screw and watch for bubbles through hose.
3. close bleeder screw
4. let off pedal
5. Check MC and add fluid if needed.
6. repeat steps 1-5 a BUNCH of times
So, if anyone has any ideas please let me know because I am just about ready to take the bike to the shop.
thanks,
Dave
Posted by: dirt bike dave---------------------
You must have boiled the fluid bad and got lots of air in there. Enough so that pushing the pedal is not generating enough pressure to force the bubbles out from the high part of the line.
A power bleeder would probably solve the problem.
A free alternative is to remove as a unit the caliper, line and reservoir. Hang it straight on a wall over night. This will cause the bubbles to rise to one end of the line. I would hang the reservoir end up high, take the cap off and let the bubbles exit out the reservoir. Tap the line a few times to break loose any bubbles that are clinging to the inside of the line.
Posted by: rmc_olderthandirt---------------------
I am not buying the "boiled the fluid" theroy. Boiling is usually a reversable process, once it cools down it will condense back into brake fluid.
Regardless, the steps stated to bleed the brakes should have cleared out any bubbles in just a few cycles. If you are continuing to get air in the lines then it has to be coming from the master cylinder. I suspect that the master cylinder needs to be rebuilt/replaced.
Rod
Posted by: whenfoxforks-ruled---------------------
Open the bleeder, depress and hold the brake down, close the bleeder. Repeat. I still believe if the master cylinder seals are bad, it would leak?
Posted by: rmc_olderthandirt---------------------
I always have pressure on the line before I open the bleeder but I doubt that it would make a significant difference. Just be sure to close the bleeder before releasing the brake.
I would also expect there to be fluid leaking from around the master cylinder if the seals were bad but I can't explain the symptom any other way. Any spot that air could leak in fluid would be able to leak out.
It is also possible that the high pressure line between the master cylinder and the wheel has a break/crack in it. Again, I would expect fluid to be leaking out like crazy if this was the case.
Rod
Posted by: Scooterb---------------------
I had the same issue on my bike
and it turned out to be the Master Cyl
If the seal in the MC is bad or is bypassing it will not leak but wont build enough pressure to bleed the system
Posted by: dave2005---------------------
well, from what I have heard and looked at, I believe it is my MC. Now my next question is, should I rebuild it or should I just replace the whole thing.
Don't you guys just love my questions! 
thanks a ton everyone for the help
Dave
Posted by: Scooterb---------------------
I tried to rebuild first .....that was a waste of $$ and time
Just go with a new one and you know what you have
Posted by: whenfoxforks-ruled---------------------
On the hondas, you had to buy the whole kit. Stretching the rubber over the piston was tricky for me, the first 2 times! They do not sell the rubber separate, go figure? When I do it again, I will order the master cylinder!
Posted by: dave2005---------------------
how much am I looking at spending on a new master cylinder?
Posted by: Ol'89r---------------------
Click on the Service Honda link on the top left side of the home page. They have an online parts finder and offer great discounts.
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