Topic: Master Cylinder Replacement

[IainC]

So I picked up a 79 CB650 earlier this summer, and have really been having a ball riding and working on it, and have gotten mostly everything I've needed done to make it run as best I can, however theres one last thing driving me nuts. The master cylinder for the single front break, has a bloated reservoir which is slowly leaking and making me nervous. I top it up every week or so just to keep it within the proper fill level, however I'd love to get this replaced.

I see all kinds of replacements around, but I'm not sure what I can go with that will work. Its been hard to research and find an answer to what will be safe and most effective to use. I'd rather not fork over a ton of cash for an original, for a couple reasons. First its extra money to spend to try and track down a used and likely not as good condition as a new after market piece, and two, the original IMO is ugly as hell. So what should I be looking for? I'm assuming I'll need to know the connector diameter, but beyond that I'm lost. I was told by the guy at one of our local bike shops he can order in a replacement but it's going to cost me over 100$. I have a feeling there are a ton of other options for me on-line at quite a bit less.

So to sum it up, what should I be looking for in a replacement master cylinder, for a single disk, for my 1979 CB650? And also, does anyone have any recommendations to particular ones they have used or any tips on getting it installed correctly.

Thanks,
Iain

[XN]

I just ordered this one from ebay. Works good and has a switch built into the master cylinder so if you want to ditch your stock switch you can. FYI he lists the same master cylinder for a ton of different bikes. Just look in his ad for one for a 7/8 inch bar with a 14 mm bore and a 10mm banjo fitting. He mostly has buy it now adds but does do the auction ones and I picked mine up for 49.99 with out anyone bidding against me.

His user name is usa-motorcycles-inc

[IainC]

Thanks for the quick reply. looks good. So should I be looking for 14mm bore with the 10mm banjo fitting?

I've never delved into the world of brakes a whole lot, and want to get this right. It's very hard to find literature on these old bikes that gives such in depth measurements and it makes for figuring out which parts I can use very difficult. I notice on ebay there are all kinds of other master cylinders available, but it's just so hard to know if it will work or not.

[XN]

#1 thing is make sure it will fit the bars so 7/8" bars. I'm not sure what bore size your bike came with. If you have a manual look in the brake section and it will tell you the bore size. My K8 came with a 14mm bore. If you go a smaller bore than stock you will have to actuate the lever more If you go a larger bore than stock you won't have to actuate the lever very much.

[tank410]

I have a master cylinder form a Vulcan (I think), The previous owner had it install on my Cb 500. It work really well with the stock caliper, but I do not need it since I am upgrade to dual disc. It is all silver with a round metal reservior. The only problem is the mirror post is broken. I sell it for $30 plus shipping. I also have the orginal but I beleave it needs a rebuild.
If you are interested pm me

Tim

[IainC]

Can anyone confirm the exact size master cylinder I need? I've checked my clymers manual with no luck. I just want to be sure before ordering anything online, especially if I decide to order used from someone. I know my bars are 7/8 inch for sure, just not sure about bore size.

[tank410]

Here a link to the manual
 http://cosky0.tripod.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://cosky0.tripod.com/sitebuildercontent/sitebuilderpictures/page15-01.jpg&target=tlx_new

You have either a 14mm or a 16mm.
and the caliper piston is either 43mm or 38m

The 14mm is what came on CB500s , 550, and 750 with single disk.

I think the 16mm must be for dual disc set ups.

But I am really just shooting in the wind.

You might want to check out this site
http://vintagebrake.com/mastercylinder.htm