Caliper Story

There have been plenty of threads on bleeding stock calipers. This is different.

I'm rebuilding a bike that was partly built and the previous owner who gave up when he could not get the brake bled. He tried an aftermarket master cylinder and still couldn't get it.

I find them to be a PITA compared to others but I always get it done.

The caliper he had was included so I went about making it look good and getting it spotless inside. That's when I noticed the problem with bleeding. The factory stopped slightly short of drilling the inner passage into the inner chamber. When the tip of their drill poked through it just bent a bit of metal up like often happens with drilling. When I ran a piece of safety wire through the bit of metal broke off but the safety wire still didn't make it through the hole smoothly. So, the already small passage (about 7/64") was way smaller than normal at the chamber end (probably less than 1/32").

Easy to fix but I didn't have a long enough 7/64" drill bit so I ordered one and am waiting for it to arrive.

Since the brake fluid goes in that passage while the air comes out of it, you are least need an open passage if you hope to bleed it!

Hard to believe that it left the factory that way and that bit of metal stayed there for around 50 years!

You can bet I'll check everyone I restore from now on!

Thanks Greg, sounds like they didn't have a long enough drill either !!

I ran a slightly larger drill through all mine (3mm I think, and 3.5 through the feed passage ) and like you say, although not the easiest to bleed I've never had an issue. It just takes time.

Oh, and I put a thin piece of rod in the inner (bleed) passage when running the drill through the crossover passage so's not to drill across it and create an un-bleedable cavity

I posted a problem bleeding a 13 mm master cylinder a year ago, it still is not like it was. I have long drill bits I'll try later Thanks for info

Greg
I noticed that andover norton now sells a pressurized brake bleeder for commando in there tools section. Anybody try it?
George

All fixed. 6" long 7/64" bit turned with fingers only and I have a nice passage now. The bit only has about 1.5" of "bit" the rest is shaft so no chance of damaging the bleed seat.