Brake nightmare

[xsmoley]

Hi all,
So close to finishing now and getting her registered the only thing left now is the brakes (and the popping right cylinder!).
Having a nightmare trying to get the old pistons out but determined to succeed. as I want to put twin discs on my 75 stock XS I had bought another calliper from ebay which seems easier to work with than my originals pictured on the left. I notice there is a slight difference in the castings and was wondering if anyone knows why and is there any reason I could not use the set pictured on the right until I can get the others set up ?
Also my master cylinder is as good as a chocolate fire guard and I need to find a replacement. Someone on ebay is selling repros with a 5/8 bore which look really good. Does any one else have any better suggestions !?
Sorry for such a long message but our British summer only lasts for another 12 hours and would love to have her on the road asap.#
Thanks all
Dave
ps have sent a picture of her as she stands

 

[xsmoley]

Sorry my originals are on the right not the left as I said

 

[5twins]

Your style of caliper has the bleed nipple on one half and the line connection on the other. Fluid transfers between halves through that small center hole between the 2 holes that bolt the halves together. I see you succeeded in getting one piston out of each assembly. That's what usually happens. When you blow compressed air into the assembled caliper, the piston that is less stuck will come out, leaving the really stuck one still in there. Now you need to isolate the caliper halves from one another so when you blow air in the side with the stuck piston, it stays in that side. Cut a small square of aluminum sheet and bolt the halves together with it trapped between them over the cross over port. Now you can blow air in either side and it will stay there.

 

[xjwmx]

Perhaps you could put the piston that came out back in, just enough to seal, and hold it there with a c-clamp or vice grip or something. Then let the air blow out the other one this time.

I didn't know early years had two pistons. Reason #83746 that Specials are better than Standards!

Also, if you do it Twins' way, you could probably use something besides aluminum it that isn't convenient. Gasket material, slice of plastic milk carton, etc.

 

[xsmoley]

Thanks again 5twins it sounds like a good plan !

 

[XSLeo]

The differences don't matter as far as funtion goes. I think different suppliers used on different years just made them differently.
Your stock single dise brake M/C was a 5/8 inch or 16 mm bore, they used a 22 mm bore on the dual brakes. You can try the 5/8's bore M/C, It well give a much stronger brake, maybe too strong. On my 75 with the later 35 mm forks with the later single piston calipers the stock 14 mm bore M/C is perfect, good feel, very strong. Easy two finger pull.
I have a 12.7 mm bore M/C. With this M/C a very gentle one finger pull will almost lock the brake. It can be gotten used to but I didn't feel comfortable with it.
So, try the 5/8's bore and see how it feels. If two strong, try a bigger M/C, like an 18 or 20 mm.
Leo

 

[xsmoley]

Thanks xsLeo very useful info there. Have just ordered the repro M/C (16mm bore) and will use it on the single disc set up. Next year I will put on the other and see how it goes with that.
Thanks again.