Front Brake Issues

[theckeler]

I replaced my front brake master cylinder on my KX250 and can't get it to pressurize. I keep squeezing the lever and it never tightens up and getting no bubbles. I put it all back together with no parts missing and correctly I think. I then snagged an extra master off ebay because I thought maybe I put it together wrong but that one does not work as well, I even used the line they sent me too. Guy said it worked fine... I did work on my KDX front and it bleed fine, I've done car brakes and never had an issue, anyone know what is going on?

 

[IndyMX]

It can take a very long time to get the front brake bled properly.

I replaced the fluid on my front brake on the 450 last summer, it took about 45 minutes to get it right.

Keep working on it.

Are you bleeding with the MC cover off? if not, take it off.

Plus, use a wrench and tap the line while you are bleeding.. that'll help break the air bubbles loose from the inside of the line.

Keep at it and you'll get it.

 

[theckeler]

Thanks I'll keep working at it and give the wrench tap a try. Ya got the cover off. Wondering too if it will help putting fluid directly into the caliper via a syringe, just to get it going?

 

[whenfoxforks-ruled]

Pre-filling the caliper is good. Not a big fan of the squeeze 5 times then bleed, but sometimes it loosens stubborn bubbles. Power bleeders are as good as the guy using them. Put a tube on the bleeder into a cup of fluid. Squeeze and hold, bleed and tighten. A lot of times!

 

[Someone]

I leave the cap off the master cylinder, then pull the lever all the way in and then let it SNAP back out. Do this about a zillion times. This seems to let out air bubbles a bit better than just squeezing and squeezing. I have a mighty vac now, it takes a few minutes to replace a brake line now (or replace fluid).

 

[dirt bike dave]

You might have one large bubble in the arch of the hose. Normal bleeding can have a hard time moving one large bubble trapped at the top of the arch.

FWIW, you might have better luck pulling the entire assembly (master cylinder, hose, slave cylinder) off the bike and hanging it straight on the wall for a few hours. Tap the hose every so often with a screwdriver handle to break any bubbles loose, so they will rise up to the top of the hose.

You can either hang it with the master up, so the bubble will come out there, or slave cylinder up, so the bubble will come out the bleeder.

Take the hose off the wall and bleed off the bike with the hose straight on the ground (no bubble catching arch). This has worked for me in the past.

 

[oldguy]

I always back bleed from the brake to the master and have had great luck getting it done. Here is a thread about bleeding and at the end is a picture of the bleeder I made myself for under $10 that works great
http://www.dirtrider.net/forums3/showthread.php?t=169435&highlight=bleeding+brake

 

[theckeler]

Ok, squeezing and sqeezing, tapping and tapping... a lot of bubbles, worked about 30 mins at it and it seems to be going ok. Going to head out the garage today maybe and do some more squeezing, hopefully it will go. Thanks everyone for their help!

 

[theckeler]

It's good now, duh ha... I should've asked before I got that other caliper and cylinder off ebay but I only paid $30 so I guess I have a backup now. Took a while to get it to go, think 45-50 mins. Thanks everyone.

 

[IndyMX]

Once it starts getting good, it happens fast.. But it takes so long to get it to that point. Patience is your friend. ;)