Another issue I've been having, is my front banana caliper. After installing new pistons and O-rings, the rear works great but with the front caliper, I have to squeeze the brake handle 4-5 times to build up pressure. It will hold until I release the handle then when I hit the brake again, it's deja vu all over. Bled it numerous times but no dice. So last night I pulled the caliper with the intention of clamping the caliper on a step ladder thinking with the caliper high above the master cylinder, I'd be sure to get all the air out. Well, when I split the caliper, there was a very tiny amount of brake fluid around the piston, but not enough to wet the pads and rotor. I played hell getting the new pistons and O-rings in last time. Any suggestions for an easier rebuild?

 

Multiple pumps makes me think master cylinder rather than caliper.

 

First off there should be no fluid seeping/leaking past the o-ring seal ... Assembly is usually easier by installing the square cut seal ( o-ring ) in the groove then seating the outer dust boot in its groove then placing the piston of the dust squarely and applying a light steady blast of air ( carefully ) with a blow gun directed into the inlet port of the caliper ... this will expand the dust boot and allow the piston to seat into the boot then apply light pressure to press the piston past the square cut seal and you should be good to go ...

 

Thanks for the responses. Not to rule out the master cylinder, but it is brand new and was bench bled prior to install. Of course, just because an item is new, doesn't mean it's not defective. The pistons I used were purchased from a reputable vendor and are an extremely tight fit. I cold soaked them at 0 degree F for 24 hours just to get them to slide into the caliper bores and then used a large C-clamp to fully seat them. With that small trace of fluid, I suspect I nicked the o-ring.

 

A warped rotor will do that as well.

 

Once you get your leak solved, the way I bleed bananas is to take the caliper off it's mount and place it underneath the master cylinder. You want a straight line going up from the caliper to the MC. Use an old rotor or piece of plywood to simulate the disk and put the caliper on it with the brake line (NOT the bleeder) straight up. Now, with the MC cover off, pull the brake lever SLOWLY all the way back and let it snap closed. Let it sit for a few seconds then just barely pull the lever back and hold it. You should see some air bubbles coming up. Repeat until there are no more air bubbles. This takes a while but was the only way I got my banana bled. When you think you have all the bubbles out, gently tap the brake line just outside of the MC body with a hammer handle, then work the lever some more. Sometimes there is a tiny bit of air that gets trapped in there.

carl