Topic: Brake headaches AGAIN...tried all the usual stuff....HELP!!!

[Boggins550]

Hey guys,

I have had a bear of a time with my front brake system on my bike.  I have completely rebuilt the system all the way from the MC to the caliper and everything in between.  All new seals, lines, fluid, and pads.  I have very diligently followed all the advice in the brake FAQ, and I have posted several questions.  Here are my problems:

1.  brake is spongy, and I have tried EVERY possible method of bleeding, and am getting no more bubbles in the system.  Any ideas??

2. brake is dragging to the point of glazing pads and scorching the rotor.  The caliper arm is free, not bound up.   I have lubed everything I possibly can with silicone lube, checked movement of the piston, and it DOES actually retract when I release the lever.  I have tried to adjust the stationary pad, but it seems when I put both bolts in the caliper assy. that it binds up the caliper and rotor somehow.  Does anyone have a diagram?  Do I have my caliper arm or disc mounted the wrong way?  Right now, I have the arm directly against the fork with the fender mounts, and then the washers and bolts.  The disc has the hub pointed AGAINST the wheel.  I am completely at a loss here!!!!!  It looks correct and I haven't been able to mount anything any different way....HELP!!!!!

Thanks!

Erik

[WHALEMAN]

1 Get a speedbleeder.
2. post a picture.
Dan

[Steve F]

When you said you rebuilt everything, I'm wondering if you cleaned out the groove for the caliper seal thoroughly.  These calipers have a habit of collecting the infamous white crud behind and around the groove which prevents the seal from retracting the caliper piston correctly after brake use and release.  This movement is miniscule, as the seal  extrudes slightly under pressure and returns to original shape when released, pulling the piston back with it, and is essential to releasing the pad from the rotor.  Be sure that the caliper adjusting screw that sets the staionary pad clearance isn't too tight, and the pad is just barely touching the rotor.
That's all I have.......
Steve F

[Spanner 1]

My guess is that the 'cup' seal in the master cylinder is backwards...spongy handle, and the second hole in the m.c. reservoir ( the hole nearest the output side ) is blocked.....brake wont release , but the pressure is low anyway due to the seal incorrect.......so result is brake drag rather than brake 'locked' which is more usual.....

[Boggins550]

Hey all,

Thanks for the replies.  As for the caliper groove, it got cleaned out thoroughly with a dental pick and an allen head wrench.  The seal is brand new and the piston moves freely in the caliper. 

I did find that the brake line was bound up and it wasn't allowing the caliper assy. to move freely with the rotor.  I had to bend the brake line at a different angle and that seemed to fix the dragging. 

As for the pressure and the MC, the cup seal you speak of is the one that goes between the spring and the piston, right?  There was only one way that cup could go, and I made sure I looked at several diagrams before putting it in.  Currently, the open side of the cup is facing the spring, and the flat bottom is against the piston.  Is that not correct? 

The only other thing I can think of is that the banjo fittings are not perfectly lined up.  Does that make a difference or do they work in any position?  Those are awfully small passages.

[Spanner 1]

Yep,you have the 'cup' seal in the right way......I know it's maddening but there has to be air inside the system if the lever is still spongy.....my 2c.  Banjo fittings should not be critical as to the direction they are facing......

[my78k]

+1 on the Speedbleeder. Best 8 bucks I ever spent!!!

Dennis

[Duke McDukiedook]

I assume you didn't get that silicone fluid in contact with any of the brake fluid surfaces, correct?
I assume you are using DOT3 brake fluid, yes?