At a loss on mushy brake

[oldguy]

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?

 

[ellandoh]

only one part of that system not mentioned is the disk. could it have overheated and glazed over??

 

[oldguy]

only one part of that system not mentioned is the disk. could it have overheated and glazed over??

I guess I had not thought about that but guess the lever would still feel hard when using on the bike stand

 

[nikki]

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.

 

[oldguy]

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.

Thanks but that is a trick I have used for years as well :nod: I tried it last night and it helped but then a couple hours later back to mushy. :bang:

 

[Uchytil]

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.

 

[ellandoh]

something overheated in the caliper when he was riding with the sticky lever??

 

[Wolf]

Dave,
I told you not to use beer as brake fluid...it's a Yamaha, not a KTM!!

Glad I could help :)

 

[oldguy]

Dave,
I told you not to use beer as brake fluid...it's a Yamaha, not a KTM!!

Glad I could help :)

We tried Saki this weekend and still soft .....kind of like an Austrian after enough (is there really enough) beer

I tried stuffing a Brat in there as well

 

[Patman]

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.

 

[Uchytil]

I tried stuffing a Brat in there as well

Did'nt nobody tell ya that just makes it greasy.

Maybe a few backflips in da river will clean er up.

 

[whenfoxforks-ruled]

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?