Brake fluid question

[drtimm@att.net]

What is the reason for a paste like substance to have collected in behind my brake caliper pistons? I assume it is a breakdown in the brake fluid, but I'm not sure. Thought some of you seasoned mechanic could educate me on this so I could better understand what I'm seeing and know the cause. I will be changing out the old brake fluid. Thanks.

Dennis Timm
Lincoln CA

[Viking]

Do you mean inside the calipers, in the hole that the piston fits into? If any paste like substance is in there, it must be from moisture that has gotten into your brake fluid over time. I have never seen anything inside a caliper, but I have seen this sort of thing inside the brake cylinder, so it must be possible for it form in the calipers also. I would just clean it all out real well, and definitely replace the brake fluid.

[drtimm@att.net]

Yes, the paste like substance was in the piston cylinder. I'm changing the brake fluid after rebuilding the calipers. I've hit a snaffo, can't get brake fluid to move thr. the system in order to bleed the line. This is after having the pistons out in the front left brake, putting everything back and filling the master reservoir and placing the cap and diaphragm. Get no resistance on the lever. Any thoughts?

[jdvorchak]

You need to keep pumping the lever. Pump, pump, hold. Then open the bleeder at the caliper while holding the lever all the way to the grip. Only when you have the bleeder screw tight again release the lever. Repeat as necessary. Slow smooth strokes work best. It's not a race to see how fast you can pump the lever.

You might just want to make sure to bleed the MC first. Pump, pump, hold. While holding open the banjo nut and see if air or fluid comes out. Do that until just fluid comes out then move the to brake caliper bleed screw. This part is messy and fluid will squirt all over the place. I usually cover my entire bike with blankets or better yet a plastic drop cloth.

You just haven't pumped it enough. If you expect pressure, you won't get any until you have fluid filling the lines and the calipers.

If you have or can borrow a vacuum bleeder that will hurry things up a lot!

[drtimm@att.net]

Thanks for the tips, didn't know you may have to bleed the MC as well. However, I have the problem solved. A riding buddy had a vacuum pump and we resolved the problem.

Again thanks for taking the time to respond.