1980 r65 master cylinder

[trips]

I haven't been on here in quite a while, my r65 has been hibernating for a few years. I'm looking to verify that it's a 13 mm. There's so much wrong information on the internet that I'm hesitant to order the parts for a master cylinder rebuild ( I have the caliper kits.
Years ago I bought a second caliper and T fitting from a member here and converted it to dual disc due to adding a side car. I'm 99.9% sure I  never changed the master cylinder.
I can't find anything stamped on the bottom, but admittedly it's hard to see, and my eyes aren't what they used to be. Info on the internet seems to indicate 13 mm, but unfortunately I've seen contradictory info, too.
Any help greatly appreciated.
I see the site still isn't phone friendly, but I don't think I've fired up my laptop in a couple years.
Hmm, still not picture friendly either, I'll have to see if I  can reduce the sizes, I'll try posting pictures in comments.
Really getting frustrated,  I  can't attach even one picture,  so I deleted all the attachments,  site is telling me I  duplicate posted, yet there's no post visible on the site. Try again.

[trips]

Pic 1

[trips]

Pic 2

[trips]

Pic 3, funny, I don't think I even had a smartphone when I joined.

[trips]

Looks like that says 041 on the outside,  there's possibly something written on the other side, but between the brightness and handlebar,  I can't see it, I will try after dark with a flashlight.

[Barry]

The early model single disc R65 with a round reservoir should be 13mm.  That's what my 79 is.    I've just been out to the garage to look at mine and confirm that. 13 is stamped on a small boss not on the bottom but on the rear side of the casting. I agree it's not easy to see but it's there. Loosening the clamp and rotating the whole assembly forward may help.

The rebuild kits are not cheap and you might want to consider the option of  a used 12mm master cylinder from the 81 - on models which will improve the brakes.

[trips]

Thank you. $94, I can do that.

[Tony Smith]

Rebuilding a round master cylinder is still possible, the issue is that if you take the tank off it will probably break and you can't buy a new one.

For that reason I suggest you buy a new square tank master cylinder, either 12 or 13mm, fit new braided hoses and off you go.

If you do get the tank off in one piece them rebuild it. The good thi g is that 13mm is sufficiently close enough to 1/2 inch that most brake repair shops will have cups they will sell you for a few cents each

Switching between round and square case m/v is usually not a problem except that some aftermarket levers do not play nicely with the newer m/c.

[trips]

We'll see what happens, if it breaks then I  appreciate the suggestion.  When you say new lines, would I have to get a custom one built with the stock fitting on one and and a fitting for the square reservoir on the other, or do they both use the same fitting at the splitter? ( I converted to dual disc from single)o

[trips]

Anyone know any tricks for freeing up stuck calipers besides the usual, soaking in parts washer, putting air to them,  etc?

[Barry]

Best way is to pump them out hydraulically with brake fluid before stripping the system down.  Failing that, air or a grease gun.  Which ever way you do it one piston will start moving before the other and the moving piston will have to be held back with a G cramp to make he other one move.

[trips]

Thanks

[trips]

Thanks

My mechanic says thanks too. 😉

[trips]

The grease gun worked it's magic

[Bob_Roller]

From the factory dual disc bikes, the master cylinder was 15 mm .