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Front Brake master Cylinder


John Ellis
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Hi I'm a new member having just bought a 1977 XS 750 Special imported from Colorado.  I have a leak on the master cylinder, the diaphragm looks the worse for wear so have ordered a replacement but the leak seems to be coming from the joint between the plastic reservoir and the cylinder itself.  Just seems to be a direct joint between plastic and metal. Should there be a seal between the two and if not should I be looking elsewhere?  Thanks in advance for any help.

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Looking at cmsnl web site, very useful for this type of thing.

https://www.cmsnl.com/yamaha-xs750-2-1977-usa-canada_model8628/partslist/F-04.html#.Xrpp425FyP-

You can see in the drawing the plastic part of the master cyl is moulded in place, or at the very least not designed to separate.

It comes down to how original you want to keep the bike, there are many options, fitting more modern units to different models that do the job. Any xs, xj, fj, even vmax its a long list. They may look different but front brake master cyl is only limited by chosen style and the calipers they opperate.

 

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7 hours ago, Cynic said:

Looking at cmsnl web site, very useful for this type of thing.

https://www.cmsnl.com/yamaha-xs750-2-1977-usa-canada_model8628/partslist/F-04.html#.Xrpp425FyP-

You can see in the drawing the plastic part of the master cyl is moulded in place, or at the very least not designed to separate.

It comes down to how original you want to keep the bike, there are many options, fitting more modern units to different models that do the job. Any xs, xj, fj, even vmax its a long list. They may look different but front brake master cyl is only limited by chosen style and the calipers they opperate.

 

it also depends on the handle bar shape. American bars tend to have higher, curvier bars so there are shaped to meet those curves.
TBH so long a the bore size is the same, you should be ok. try xs650 stuff off mikes XS

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Thanks for the responses, I've fitted a new diaphragm and cover plate but am still getting a drip, next thing is to remove from handlebars and try to trace the leak.  I've also checked both callipers and replaced the pads as the originals seemed to be oily and there was a deposit of some sort on the discs.  All cleaned and reassembled but the brake is still suicidal!  Maybe I need to bed the pads in a little? Or maybe I'm expecting too much?  My other bike is a BMW R Nine T with Brembos and will stop on a sixpence!

Edited by John Ellis
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