Spiders 2009 YZ450F front brake has become mushy- It works but often won't lock until the lever is almost to the grip. It started a few weeks back when he put on an ASV lever but it must not have been machined properly because as he rode it to the track entrance everytime he pulled it it stayed slightly in keeping the system pressurized until it finally just locked the wheel up. We immediately switched back to the stock lever and he rode the rest of the day with the mushy feel.
The front pads were worn so we replaced them the next day.
next ride it was still mushy so I replaced the brake fluid and bled the system.
I then rebuilt the master cylinder as I thought i saw small bubbles up there - no change
Next I rebuilt the Caliper in case it had overheated and caused a leak there- no change
last step was replacing the stock brake line with a steel braided line and again changing out the fluid and bleeding.
Anyone have any other ideas? It is slightly better and maybe after riding Tomorow it will firm up with the new parts?
Try zip tying the brake lever pulled in overnight.... just a little tip I've heard work for some people before, basically to get any air out of the line. Might not work for your issue, but worth a try.
Try zip tying the brake lever pulled in overnight.... just a little tip I've heard work for some people before, basically to get any air out of the line. Might not work for your issue, but worth a try.
Sounds like you've covered all the bases. Sounds like there's still air in the fluid. I went with a reverse bleed years ago. I have a hand vacumm pump that I use. If all of the components are absolutely tight it may just take more work getting out the air. If the system worked fine before the ASV was installed I'd guess it's just air that got in when that was installed.
Got a Mighty Vac hand pump? If not you can pick one up at most auto parts, Harbor Freight, etc... pretty cheap. You can use it to either back bleed or pull fluif through the system. Tap on all the pieces with a wrench to help the stubborn bubble make their way out. My front brake from a KX was the same way until I used the Mighty Vac. Sadly I need to rebuild / replace the master after 4 years of no worries.
1 air bubble Dave, rocking back and forth somewhere? Or a loose/bad connection somewhere? You are down to the caliper and pistons. A warped rotor is way to easy, but the thickness is still good?