Rigging the front brake

[Jeff Gilbert]

I've had some issues with my front brake on the 125 pumpkin. I have great front brake BUT, I would like more lever. Like the fellow on the brembo thread I have to pull the lever too close to the bar to engauge the brake. There is no air in the line and I have new pads, I simply need more piston push. I experimented and this seems to work, I placed a stainless BB ( yes from a BB gun) in front of the plunger on the mater cylinder. This sort of extends the adjustment screw so it will push farther. I now have excellent front brake though the bike is on the stand in the garage, tomorrows race will tell for sure.

My question is Am I in any danger of the BB restricting the plunger and getting caught with absolutely no front brake?
Secondly, does the adjustment screw wear on the tip that pushes the piston?

 

[Tahuya Rat]

Is there room for the bb to get jammed in between the side of the plunger and the housing? I don't think wear on the adjustment screw has ever been the issue - I've seen an entire line of new KTMs on the dealer floor with the adjuster screwed in all the way and still too much play. Be careful with that bb fix, if I remember right the end of the plunger is rounded, I'd be more concerned you could end up getting it jammed in there. One other thought, does your front brake "pump up" during a ride, or when left overnight with a tie wrap holding the lever in? If so, you could be trying to make up (in adjustment) for a sloppy bore and/or worn m/c seal kit, which could lead to a lockup once the brake fluid get's warm and the seals expand a bit.
Someone had posted some data about a year ago on the Holeshot board about the distance the internals had to retract so your caliper will release, don't remember exactly what, but I do remember an experiment gone wrong of mine 20 years ago where I had "overfilled" the m/c resevoir on a street bike with twin disks by topping it off completely with pads off, pistons slightly engaged, then putting the pads back on. Finally I had brakes right out at the start of the lever pull instead of in by the bars. Rode about 10 miles, gave 'em a big grab, and down I went, brakes completly frozen. Real problem with the brakes, as I learned later, was that it was a dual disk setup with a master cylinder for a single disk (custom setup from the previous owner). The m/c simply didn't push enough fluid to engage until the lever was halfway to the bar.
Let us know how it goes today.

 

[marcusgunby]

Best thing is to adjust the red knob to a few turns from fully in, then remove the red knob at the end, adjust it in a few turns with pliers, then refit the red knob, this will give you a few extra turns of adjustment.

 

[Jeff Gilbert]

The front brake was awesome today. I still don't like the idea of my temporary fix and will change it but it did work flawlessly. The bb is about the same diameter as the ball that's on the end of the adjuster screw and I didn't have any problems with the screw slipping out of the housing, that would lead to an undesirable effect. :eek:

Marcus, I need slightly more than just a couple of turns, more like about 2mm. I have some machines at work that I may can take some parts off of and make me a longer adjustment screw and round off the end of it so I don't damage the m/c.

I don't have a leaking problem and the brake doesn't pump up, that's not to say that the piston in the m/c isn't pushing enough fluid. I probably will rebuild the entire brake system before I resort to manufacturing an adjustment screw.

Once again, the temporary fix worked wonderful today but I don't think it's a long term fix.