RD350 front brake

[forexer]

Last Friday I picked up a clean 73 RD350 that had been sitting for years. It needs all the usually stuff done to it from sitting for so long so I started today messing with the front brake master cylinder and ordered a rebuild kit for it.

Here's my question - is that teeny tiny hole the one that usually gets clogged in the master cylinder supposed to go all the way through?

I cannot remember if that hole is supposed to be open or not - I've tried using .020 safety wire and it will not go all the way through so I thought I'd ask.

If it is supposed to go all the way through then does anyone know the drill size so I can ream this hole out?

Thanks!

[pidjones]

It goes through to the piston cylinder. I use a high "E" electric guitar string (.009", I think) in a pin vise to work my way through them, then flush thoroughly with brake cleaner.

[1976RD400C]

Acetylene torch tip cleaning set of little wire pokers works good too.

[forexer]

Can someone else please confirm that this hole circled in red goes all the way thru

I shined a bright light in the opening and I can't see any evidence of that hole going all the way thru even when looking from the underside - also I find it hard to believe that it would be that stubborn to clean out.

Anyways I'd like to know for certain before I put this all back together again because the circlip and rubber boot can be a pain

Thanks

[Striker1423]

That is the return hole. If you apply a brake and the return hole is clogged your brakes stay applied.

All the way through? I do believe it goes through to the piston side.

[m in sc]

it does go thru to the main bore. do -not- make it bigger.

take master apart before clearing it out.

[forexer]

A BIG thanks to all that replied - I ended up drilling it out with an undersized drill bit - I would of never thought that it could get so clogged up where safety wire and a guitar string did absolutely nothing but bend.

Thanks again

[Striker1423]

A BIG thanks to all that replied - I ended up drilling it out with an undersized drill bit - I would of never thought that it could get so clogged up where safety wire and a guitar string did absolutely nothing but bend.

Thanks again

On another note, if you have guitar string or steel braided wire and a drill that will chuck it up. It will act as a drill bit. That's how I de-Caswelled my tank crossover tubes. Yeah, I couldn't figure out how shoving playdough inside the tubes would prevent the top of the hole from being clogged with it.