Front Master Cylinder Rebuild Gone Bad

[ropethebike]

Well............I finally found time to rebuild the master cylinder and now I am worse off than I was. I work on alot of trucks and farm equipment, so I am a pretty fair mechanic, but I don't know very much about working on dirtbikes.

The rubber pieces on the plunger shaft that I took out of the MC was detoriated and one was torn a little, so I figured that to be the problem.

I installed the new kit and a new brake line while I was at it. Now the lever pulls really, really free and I can only get a dribble of fluid out the bottom of the line. The only thing that I can think that I might have done wrong was I put a little fluid on the rubber pieces prior to re-installing..........thought this would keep the metal from tearing the rubber but perhaps it prevented a good seal??

If I remove the brake line and hold my thumb over the MC line hole it will pressure up and squirt fluid past my thumb it I give it a little space by slightly moving my thumb.

I just totally don't understand what could have went wrong............this appears to be a simple task............anyone got any ideas??????

thanks in advance
rtb

 

[Rotorranch]

Fluid on the seals won't cause a problem. In fact it's recommended.

Sounds like you just haven't got it bled yet.

How are you trying to bleed it?

Rotor

 

[ropethebike]

Well, I thought it was like a truck master cylinder, only smaller, so I buttoned everything back up and tried pumping the brake several times and then held the brake lever in and cracked the bleeder valve, which I had a piece of hose on and the other end in a jar of fluid.

But, this didn't work. Please tell me the proper way. It seems like the MC isn't building pressure like it should, not filling the line with fluid for that matter............

thanks
rtb

 

[Rotorranch]

LOL...you would think that would work, but the cylinder displace a lot less fluid than a car or truck.

I normally use an air powered vacuum bleeder. Vacula. :)

http://usa.vacula.com/newsite/produkter/image.php?product_image=1090505618_04_drain_man_400x400.jpg

If you don't have one handy, try the bottle and hose method. Get a piece of hose that fits the bleeder tightly. Submerge the other end in a bottle with some brake fluid in it. Crack the bleeder, and pump the cylinder, keeping the reservoir full. When the bubbles stop coming out, squeeze the handle, and shut the bleeder.

Try that and see if it helps.

Rotor

 

[IndyMX]

After just cleaning the front caliper real well and changing the fluid, it took forever to get a good feel on the front brake. I must have worked on bleeding that thing for a solid hour.

I also recommend the vacuum bleeder. Takes way less time and effort.

 

[ropethebike]

Thanks Guys !

I got it working today. I think the problem was the hose I used on the bleeder valve wasn't snug enough.........I think yesterday I used some 5/16 and it was too loose it seems.

Today I picked up some 3/16 hose and in about 15 minutes I was in business.

Thanks again
rtb