2004 CRF450R front brake failure

[Augoose]

I was farm riding last weekend and all of a sudden my front brake started to fail where I couldn't stop the bike solely with the front brake- not even close. The pads would grab but seemed not to create enough friction to actually stop the bike.

I could not detect any leaking fluid anywhere and the level in the reservoir was full and where it always was. No indication of bubbles in the reservoir either. Visually, the pads were starting to get low so I was hoping that's all it was- new pads did not fix the issue nor did bleeding the system. No air bubbles when I pump the lever either.

I checked my disk thickness which was 2.8mm (service limit according to the manual is 2.5mm).

Based on some searches, seems that a caliper rebuild is the next step? Possibly the pistons are leaking air or are binding? I did notice that when I changed my pads, the pistons were extremely hard to compress (yes the reservoir cap was off). I had to take a piece of wood flat across the pistons and use two small woodworking clamps to press them in. Should I have been able to compress them by hand as shown in the service manual? Is that likely part of the problem?

During the bleed, a squeeze of the lever did not produce a nice squirt of fluid - more of a dribble.

Thanks

Edited September 27, 2019 by Augoose

[Augoose]

Well I got a wild hare and pulled the caliper - used my air compressor to try to pop out the pistons - one popped out and the other was frozen. Found my issue. Once I finally got it out I could see a line of dirt on the side of the piston where it had been frozen for a bit apparently. Also part of the upper o-ring had squeezed its way out and was jammed in between the piston and the cylinder wall.

New rebuild kit on the way.

Hope everyone has a nice weekend.

[Shawn_Mc]

Replace the line too. The piston was stuck for while, but the other one still worked. The reason it stopped working all at once is an internal leak in the front brake line. Ive seen it at least a dozen times. Spend the money on a decent stainless braided one. You'll be amazed.

[Augoose]

29 minutes ago, Shawn_Mc said:

Replace the line too. The piston was stuck for while, but the other one still worked. The reason it stopped working all at once is an internal leak in the front brake line. Ive seen it at least a dozen times. Spend the money on a decent stainless braided one. You'll be amazed.

Thanks Shawn - will do!!

[Spitz85]

Becareful with compressd air, good way to hurt or lose a finger or damage the caliper if it builds pressure a rockets the piston out.

[Augoose]

Yup! Regulated to 80 psi. Pistons popped right out into a towel.

Everything is back together now. Brakes work well - a bit squishy so I must still have a bit of air in the line. Will continue cycles of squeezing the brake lever, releasing the bleed screw, tightening the bleed screw, and then releasing the lever.

[Shawn_Mc]

Try this:

do the standard pump, hold, bleed, but continue to hold, Hold the lever to the bar. Go ahead and throw a ty wrap on it. Now, tap on the reservoir. Look for the bubbles. Run the lever back and forth etc. There's probably air in the back side of the master cylinder piston. When that happens, the master doesn't push properly. I use a vacuum bleeder and run the lever while using the vacuum and simultaneously filling the reservoir. It's a bit of a circus, but it works. If youve got big thick grips, take the throttle off. You want that lever to be pulled in as far as it can be.

[Augoose]

Awesome - thanks Shawn.

I also ordered one of the bottle bleeder kits so I'll try it again with your advice above. I was tapping the MC and the line before but not with the lever held in.

[Augoose]

Shawn's advice plus this little baby worked perfectly!

My 13 year old was off the hook as a helper.

Edited October 5, 2019 by Augoose

[notoriousE-R-I-C]

I just inject backwards from bleeder up with the master cap off injected by a printer ink syringe.
If ABS, then you have to fill at two points

[Shawn_Mc]

5 hours ago, notoriousE-R-I-C said:

I just inject backwards from bleeder up with the master cap off injected by a printer ink syringe.
If ABS, then you have to fill at two points

That depends on the ABS system style. But lets not get off track here.

[notoriousE-R-I-C]

Whatever the design...youre adding steps to the process.

My point, inferring non abs dirt bikes, one backwards squirt MC cap off, you're good. And this takes 30 seconds