all sorts of front brake rebuild problems. help needed....

[Guest]

So I decided to completely rebuild my front brake system complete with SS lines, new caliper rebuild kits and pads. I'm going to describe my procedure first then hopefully someone will be able to tell me what i did wrong.

1. Pumped fluid into calipers until piston came out. Cleaned out piston thoroughly using brake parts cleaner and steel wool and a derusting gel that took out 99% of the rust and left me with only a few pittings here and there.

2. Reassembled caliper using new rubber everywhere and brake grease where appropriate...etc.

3. Hooked up SS lines and fittings without using new crush washers and added some vacuum to the Right hand side caliper and got fluid flowing and saw no leaks and bled until there were no bubbles.

So basically i rebuild the right hand side caliper with no problems and bled it and whatnot, and it seemed just fine. Next is where the problems started.

4. Tried to pump the left hand side piston out but it wouldnt go out! It would move a few mm out and promptly be sucked back in as soon as the brake lever was let go of. I eventually discovered that i could get the piston to move if I opened the bleeder when the lever was depressed and shot some fluid out then closed it again and let the lever out. Repeat this 150 times and finally the piston shot out. Rebuilt the caliper and noticed it was a little more rusted on the inside than the other but again, de rusting gel and steel wool and it polished up fine and the piston was in great shape.

5. Put new seals and grease in, reinstalled piston and refitted to bike and put lines on.

6. Sucked air out of lines with syringe and pumped new fluid in system and noticed several things.
a. there was a leak coming from the bleeder screws like not the hole on top but from the threads
b. the piston was behaving the same as before....going out a few mm then coming right back in the same distance when the lever is let off.


Thats where i am right now and im fresh out of ideas. I hear a weird sucking noise too on the left hand caliper when letting off the lever so i wonder if one of the seals is not fitted quite right and sucking in some air?

what do you guys think about the going in and out piston thing??

[lordcannon88]

any help? please? shameless bump....

[gggGary]

rebuild the master cylinder?

[lordcannon88]

forgot to mention that...i already installed a new master cylinder.

[waterman]

If the piston is retreating when you let go of brake lever, than it is working properly. I am assuming that you have the bleeder screwed in tightly. Likewise the brake fluid will leak around thread when the bleeder is open, some have suggested using grease on thread to seal while bleeding to prevent air from being drawn back into cylinder.

When you replaced lines with SS, did you use two lines from master cylinder or three with the factory splitter? If two lines, you may have air in one line while the other is full of fluid.

After thinking a little about your problem, I would check to see if you have air in the cylinder or brake line of the problematic side. I have found that chasing the fluid from the master cylinder down to the calipers works best. By this I mean to fill master cylinder and then crack open attachment bolt and pump until only fluid comes out. Then proceed down to caliper and do same with that bolt. Finally bleed cylinder making sure bleeder is at highest point.

Are you putting any resistance on the moving piston? Try squeezing a wrench or some other object, this will allow the trapped air to compress and thus hopefully leave the bleeder.

Bleeding twin disks is almost always a chore, I usually get a quart of fluid and seem to use most of it. Goodluck, patience is your friend.

[gggGary]

+1 air in the lines yet.

[lordcannon88]

If the piston is retreating when you let go of brake lever, than it is working properly. I am assuming that you have the bleeder screwed in tightly. Likewise the brake fluid will leak around thread when the bleeder is open, some have suggested using grease on thread to seal while bleeding to prevent air from being drawn back into cylinder.

When you replaced lines with SS, did you use two lines from master cylinder or three with the factory splitter? If two lines, you may have air in one line while the other is full of fluid.

After thinking a little about your problem, I would check to see if you have air in the cylinder or brake line of the problematic side. I have found that chasing the fluid from the master cylinder down to the calipers works best. By this I mean to fill master cylinder and then crack open attachment bolt and pump until only fluid comes out. Then proceed down to caliper and do same with that bolt. Finally bleed cylinder making sure bleeder is at highest point.

Are you putting any resistance on the moving piston? Try squeezing a wrench or some other object, this will allow the trapped air to compress and thus hopefully leave the bleeder.

Bleeding twin disks is almost always a chore, I usually get a quart of fluid and seem to use most of it. Goodluck, patience is your friend.

I'm using the factory splitter. Also when the lines are taken off and full of fluid is it normal for the lines to drain as well as the M/C drain? Back to the piston going back into the caliper thing---isnt it suppossed to go out further and further everytime the lever is pulled? to compensate for pad wear? and this is what causes the major pain in changing pads because you have to compress it back into the caliper to account for extra pad space? And good call on the pressure on the piston and caliper i will try pressure tomorrow.

[waterman]

I think you will see more retraction with your rebuilt calipers since there is less friction holding your pistons out. You will be able to manual push the pistons back into the cylinder after a rebuild. You may need to check splitter for air also.

A little pressure on the pads will help with bleeding, don't ask me why I know. Wasted afternoon on that one.

[lordcannon88]

Indeed. Thanks a lot ill let you know how it goes tomorrow.

[madjack57754]

Getting all the air out is a problem, especially if you have never done dual disks before. With the master cap off pump the break lever lightly and watch for a small stream of bubbles. If you see them you still have air in the system
Check the search function on brake bleeding or go to Basscliffs web site for more info. Lots has been writen about the process. If you still have problems ask here again. Most everbody here is willing to help.

http://members.dslextreme.com/users/bikecliff/