Can someone help me out please?

[drz125L]

Ive just picked up an 03 CR250r. The rear brake does not work. I have put in new dot 4 and bled them off, but the brake doesn't work. I'm kinda new to disc brakes. Can anyone give me some troubleshooting tips. The rear brake lever funtions fine, it (the brake) just won't grab! Any help/tips/advice would be appreciated. Thanks in advance forum members!

[MXtras]

The brake system is really simple. The master cylinder provides pressure and volume. The hose delivers it. The caliper uses this pressure and volume to push out a piston and provide the squeezing.

So - to verify the master cylinder is in fact producing pressure and that the hose is delivering it, push the pedal down firmly and crack the bleeder. You should get a stream of fluid coming out from the bleeder. As this fluid is expelled, the pedal will drop. If this is occuring (it sounds like it is from what you posted), your master cylinder and hose are doing their job, so the caliper would be the likely culprit.

The pistons can get bound up - especially if the previous owner did not bleed often. One thing you can do is to compress the piston back into the bore using firm hand pressure in the right spot and then pump the pedal - the piston should come out and apply pressure to the pads.

Now - you said the brakes won't grab. Not at all?

How far does the pedal go down?

If you push the pedal all the way down and hold it, does it drop at all?

Is the piston in the master cylinder bottoming out (full-stroking)?

This would be a 20 second diagnosis in person.....it's kind tough to say without touchy-feely.

Scott

[drz125L]

Thanks MXtras!:
I'll have to check all this out. (I'm heading to a Canada Day Party, kinda like your 4th of July) The brake pedal does go all the way down, the master cylinder is producing pressure as I had a good bleed going. Do I need to remove the caliper asssem. to push the piston back in? Sorry for all the questions, but up til now I've always had new 4 strokes (jr.80 and a drz125) so I never really had to wrench them. I am willing to do the work though and have a decent set of tools. Really appreciate the reply, I'll update tomorrow on how I made out.

[MXtras]

No need to remove the caliper. The caliper floats, so you need to look at how the actual caliper is mounted and you will likely be able to figure out how to force the caliper piston back in the bore. You might need a small C-clamp, you might not. On a well maintained bike, it can be done by hand - I do it everytime I wash the bikes - especially after a mud race.

Again - this might not be a fix, but it might help figure out the next step. If the piston is backed into it's bore, it will be easy to see if pumping the pedal will make it extend.

Are there any leaks in the system?

Scott

[drz125L]

There are no leaks, i got the piston pushed back, but when i push the leaver it does not move at all.

[avi-b]

one importent thing mxtras forgot to tell you.
to bulid pressure in the system you should pump for about 10 seconds every time before you open the bleeder.
and keep the pedal down antil you close the bleeder.
usually i do it in my way and i goes faster.
i dont use the bleeder becose its make the work longer and its easy to broke it.
in use the bonjo bolts its easier and faster.
i start with the bonjo that on the master cylinder and when i have a pressure there i go to the one that on the caliper.
if you have aal lot of air inside the system its can take you even 20-30 minutes.

[VAL]

Originally Posted by drz125L

Thanks MXtras!:
I'll have to check all this out. (I'm heading to a Canada Day Party, kinda like your 4th of July) The brake pedal does go all the way down, the master cylinder is producing pressure as I had a good bleed going. Do I need to remove the caliper asssem. to push the piston back in? Sorry for all the questions, but up til now I've always had new 4 strokes (jr.80 and a drz125) so I never really had to wrench them. I am willing to do the work though and have a decent set of tools. Really appreciate the reply, I'll update tomorrow on how I made out.

When you say the brake pedal goes all the way down, do you mean even when you are not bleeding the system? If so, that is, if the pedal continues to travel all the way down, even after you pump it a couple of times, it sounds like the master cylinder seals need to be replaced. A bad MC will still develope enough pressure to bleed the system, but once the system is closed, it is easier for the fluid to travel around the seals than to pinch the caliper. Does the brake pedal take a bit to return to the off position after you depress it firmly for a period of time?

[MXtras]

Originally Posted by avi-b

if you have aal lot of air inside the system its can take you even 20-30 minutes.

If you have a completely empty system, backbleeding is the way to go. Use a disposable irrigation syringe from your local animal hospital (they will sell them to you for like $1 each) and a small piece of clear tubing (local hardware store, sold by the foot). Fill the syringe with fluid, open the master cylinder resevoir, put an 8MM box end wrench on the bleeder, break it open, close it, put the hose on, open the bleeder and force the brake fluid back to the master cylinder until you see bubble-free, clean fluid coming into the reservoir. Close the bleeder, fill the reservoir to the proper level and put the cover on. Pop a cold one - you're done.

OP - if your caliper piston moves freely but the brake lever does not move it back out, there are two likely problems. The most likely is that your master cylinder is not completely bled. Another possibility is that the master cylinder needs rebuilt. It's really hard to say without the touchy feely. I guess at this point, I would suggest grabbing the rebuild kits for both the caliper and the master cylinder and rebuilding both. The parts are not all that expensive. Then you would be assured your brakes will work when needed. Both are simple to rebuild, just make sure all parts are spotless inside and out and make sure you handle the seals very carefully - you don't need to force anything together - it all goes together fairly easily. Lubricate re-assembly with your choice of brake fluid.

You would be smart to tear everything down for inspection prior to ordering parts so you can replace anything that needs replacement - like the caliper pins or the pad pins.

Scott

[drz125L]

Thanks for the advice, I am going to try these tips out, and i'll let you know what ended up working.

[dirtybird]

i was havin troubles bleeding my brake(02 cr250). i couldnt figure it out because i was pushin the lever down opening the valve and fluid would come out. i kept refillin the cylinder and the fluid would pour out but the pedal wouldnt stiffen up and the rear brake wouldnt grab. so what i did was actually take it for a ride and within a minute i started getting some brake then more and more. i stopped and refilled the cylinder and pushed the line a few more times and havent had a problem since. i dont know man a little different but it worked for me and good luck. on the bright side brakes only slow you down right

[MXtras]

Yeah - sometimes you can get a bubble trapped in the master cylinder - especially if you are being overly cautious and maybe going too slowly.

Once you have a little fluid coming from the bleeder, attach about a 12" piece of clear tubing to the bleeder. Fill the reservoir, open the bleeder a little and pump the pedal - don't close the bleeder screw. Just pump the pedal and keep an eye on the reservoir - don't let it go empty. Pump pretty quickly and full stroke. When the res is out of fluid, close the bleeder a bit, add fluid and repeat. It helps if you have a buddy to keep the res full so you can just keep pumping. This is also an effective way to purge any air from a brake system. It took longer to type all this out than it does to do it.

Scott

[drz125L]

Alright, an update, I am sure I don't have any air in the system. So...... I went ahead and took the caliper off and dis-assembled it. I took the piston out and cleaned it, seals out and looked for cracks/damage.(looked okay but I don't know what new ones look like, so these could be worn) When I put the seals back, the piston was extreamly hard to put back in. To the point I stopped trying and have decided to order a new set of seals.The master Cylinder seems fine,no leaks. the hose is fine. If nothing else, I'm getting some good wrench time on this bike and I'm learning.................... and so it goes