Brake Master Cylinder Reservoir O-Ring

79XStLouis

XS650 Enthusiast
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Hello all, I have not posted in a long while. I have two questions for the right persons. 1) I have an 79 XS 750 Special...not 650. Does the 650 and 750 use the same front brake master master cylinder? They look identical. 2) Does anyone have the precise O- Ring size for the reservoir cup to the metal body. I know the O-ring must be made of EPDM or brake fluid will eat through nitrile, or anything else. Any help much appreciated.
 
If nothing else comes up partzilla has lists where a specific part-number can be found and a list on where that part is used
One needs the exact type on both bikes
it looks like that --- please check if the right bikes and what part

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Hello all, I have not posted in a long while. I have two questions for the right persons. 1) I have an 79 XS 750 Special...not 650. Does the 650 and 750 use the same front brake master master cylinder? They look identical. 2) Does anyone have the precise O- Ring size for the reservoir cup to the metal body. I know the O-ring must be made of EPDM or brake fluid will eat through nitrile, or anything else. Any help much appreciated.
The XS650 O-ring is a JIS P40. If you have the same size master cylinder, let me know your address and I can mail you one. I bought a bunch when I needed them.
 
Many thanks, I would appreciate that. The front brake master cylinder is the same between 650 and 750 models. I am unfamiliar with the JIS P40 classification. Is that the size or material? I heard that only EPDM rubber will stand up to brake fluid. My mailing info is: Evan Bevirt, 9745 Meadowfern Dr., St. Louis, MO 63126. Again, thank you!
 
Many thanks, I would appreciate that. The front brake master cylinder is the same between 650 and 750 models. I am unfamiliar with the JIS P40 classification. Is that the size or material? I heard that only EPDM rubber will stand up to brake fluid. My mailing info is: Evan Bevirt, 9745 Meadowfern Dr., St. Louis, MO 63126. Again, thank you!
Hi Evan, The JIS stands for Japan Industrial Standard. The P40 describes the size. I don't remember the specific material of these but it was brake fluid rated. I'll drop it in tomorrows mail.
Gary
 
The XS650 O-ring is a JIS P40. If you have the same size master cylinder, let me know your address and I can mail you one. I bought a bunch when I needed them.
I'm having the same issue with my 1980 xs1100L. Any idea if it's the same size as the JIS P40 that you've described?
Thanks!
 
I'm having the same issue with my 1980 xs1100L. Any idea if it's the same size as the JIS P40 that you've described?
Thanks!
The XS1100 and XS650 reservoir o'ring (packing) is the same thing. The XS1100LH (1981 Midnight Special) is a possible exception in that I don't know for sure.
 
Thanks. Mine is the midnight special, I was assuming it would be the same. I can compare it to my xs850 and maybe get a better idea. Is JIS P40 the complete measurement, because I'm seeing more to it when looking it up?
The XS1100 and XS650 reservoir o'ring (packing) is the same thing. The XS1100LH (1981 Midnight Special) is a possible exception in that I don't know for sure.
 
Thanks. Mine is the midnight special, I was assuming it would be the same. I can compare it to my xs850 and maybe get a better idea. Is JIS P40 the complete measurement, because I'm seeing more to it when looking it up?
The 1981 XS1100 Midnight had linked brakes. The 1980 did not. If you don't have linked brakes, it's the same o'ring.
 
The 1981 XS1100 Midnight had linked brakes. The 1980 did not. If you don't have linked brakes, it's the same o'ring.
No, definitely dont have the linked brakes. My rear master does have the option for it, but it's just got a bolt in that extra hole.
Do you know where I can buy the oring by chance? I'm not coming up with anything definitive and riding around a bottle of brake fluid with me isnt ideal.
 
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