'06 WR450F Front Brake Very Weak

I picked up my '06 WR450F back in '10. The front brake has always been very soft (not very good stopping power). The lever is very mushy and not firm at all. I've replaced the brake line with a braided one, new pads, and obviously bled the fluid as well as I could. I've also tried taking the master cylinder off the bar and holding it up high trying to make sure I didn't have any air in the lines. Even tried a reverse bleed. When I picked up a '03 CR250R in 2011, it has power brakes compared to the WR. Even with a blown fork seal and saturated pads, the CR's brakes are much better.


Any suggestions? I have a master cylinder off a '98 CR250R that I am thinking about trying. I also have the brake caliper but I haven't really looked at it that close because I didn't think it would bolt up.

The stock brakes are fantastic, don't change components.


First, you have to expand the pads all the way out (bottom out the pistons) and keep them there while you bleed the brakes


You remove the mc cover, compress the pistons using a C-clamp, and hold them there, or wedge something to hold them there.


This will push out the air trapped behind the pistons.


Next, you must remove the bleeder valves and cover the threads in plumbers tape. You need enough to make the bleeder require a wrench to turn it. 

This will prevent air from sucking in past the bleeder threads, as you bleed the system.


Now you can bleed with vacuum or syringe, your preference. I like vacuum as it's less messy.


It will take 1/2 a can of FRESH fluid to get all the air out.

Do not use an open can of brake fluid (more than a few days) as the fluid wicks moisture out of the air very fast, and you don't want that in the brake lines........


Once you believe you are getting some pressure, pump the lever up as many times as you can, and zip tie it to the bar over night.

Do this a few times in row until the lever becomes firm.


Now, this is all assuming that your MC diaphram is not damaged, or your caliper seals are not damaged. You can't tell with the MC diaphragm, but the caliper piston seals will leak if damaged.

Edited by KRANNIE

You also need to: 


Clean the pads and disc with spray brake cleaner and a clean towel


You should also bend the metal pad springs tight, so the pads do not move at all, do not 'drop' out of the caliper. Add copper high-temp grease to the back side of the caliper to eliminate pad vibration.


Once the job is done you need to break in the pads.


You do this by getting the bike up to speed on pavement, and slowy applying pressure the brakes for 5 sec at a time, over and over. 

You do not want the pads or disc to get hot.

Repeat with more pressue on the lever, and for longer periods, letting every thing cool in between.


It usually takes 5-10 min of patient cycling of the brakes, keeping them from getting too hot, to get them to seat. 


If you do not do this, the pads will glaze from having to apply too much pressure to the lever.............


Do not 'scuff' the pads or discs with sandpaper, this makes everything worse. You can use green scotchbrite pads if needed. 

Edited by KRANNIE

Thanks for the info Krannie. I'll give it a try this week. I forgot to mention that I already have a master cylinder rebuild kit. I'll install it as I need to replace the brake light pressure switch also (I plated it).

Off topic: I've been researching '06 YZ forks for my WR and reading some of your threads. I might be able to snag a pair from a local shop revalved with new seals for around $500 or less. It's from a shop that has a good rep for suspension work.

Thanks again

Very nice Krannie!

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