Rebuild or replace front master cylinder?

pumps

Since I am putting on new braided lines I thought I would pull my front master cylinder apart and give it a paint job. Got it apart and I see the o ring under the reservoir has leaked onto the paint and there is lots of brown waxy looking stuff down in there. Scraped it all out and as I inspected the plastic reservoir I noticed cracks in it. It would be a good time to put a rebuild kit in while I have it apart but the more I look at the prices of the kits plus I don't see that mike has a reservoir I'm thinking I'll replace it.
Rebuild kit=$19.00 + Reservoir Cap & Diaphragm Kit=$34.00 plus a reservoir from ?. New master cylinders start at $69 I think . I'll go dual disc setup on the front eventually so can I get one that will run a single now and still work for a dual later? Which one to use?The Part #08-0265mike has? I'm trying to stay close to stock.Thanks in advance!

pamcopete

pumps,

Well, I would use a new master cylinder. IMHO, the only brake component that can be successfully rebuilt is the caliper, and that's because it's so simple.

As far as I know, you will have to use a single caliper MC with a single caliper and a double with a double.

When you squeeze the lever, you want the bike to stop....

gordo

Pump's, if the reservoir has cracks in it, it will eventually leak. Or worse.
You can use the master for dual disc's for one, but remember that hydraulic force is multiplied many time's over. A bigger bore on the master will give you more braking force than a smaller bore, possibly causing wheel lock on a 'panic' stop. Also, when you finally get the second disc, the brake will feel like it has less braking, because you'll be used to the bigger piston on one disc. I understand that money is always an issue with everyone, but I recommend you get the correct master first, then get the dual disc one with the dual disc set-up. Sell the one for the single disc here or on e-gay. Confused

yamaman

Pumps, check out the Vintage Brake web site, it has an application chart for the best combinations of callipers/master cyls. Any doubts you should ring MMM, as Gordo says, get it right first time!

Just for your info, old style callipers are 48mm twin piston, new style are 40mm single piston.

They recommend a 5/8ths - 16mm master cyl for 2 disc/new style callipers

Or a 19mm master for twin disc old style.

These are a guide only & not a strict rule, but these will put you somewhere where you need to be!

www.650central.com/

Cheers

pumps

Just the kind of great advice from experience that I needed! I'll go with a single for now and peddle the new/old one when the time comes. I'll get the Yamaha OEM type Part #08-0255 from mike if that one is ok. Brakes are sort of important to me. Smile

gordo

OR, you could play Fred Flintstone, but I don't recommend it.

xsleo

I'm using a 5/8, 16 mm bore M/C from an 82 Seca. I have the later style calipers, with a dual disc. The M/C works very well. The lever travel isn't very long.
I think a 14mm would be better with the later style dual caliper set up.
If you are going to use the older style calipers in a dual set up. A 22 mm M/C was stock, The 19 mm my work better.
I think using a M/C that is too big would make the lever pull harder and get weaker braking.
A M/C too small, the lever will pull easy and you may run out of lever travel before the brakes work.

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