Rear master cylinder - leak between reservoir and body

[OldGreyBeast]

A while ago someone posted a link to the o-ring used to seal the brake fluid reservoir to the MC body for the front master cylinder of the XS1100 special. I replaced that as mine was leaking. The rear one was holding fluid up until a couple days ago, now it's leaking (which sucks as I just got the rear brakes bled about 2 weeks ago). Anyone know what O-ring I need to replace that seal? Assuming you can get the reservoir off anyway.... it's definitely on there harder than the front one was.

[cajun31]

Might just be that it needs to be cleaned up under there. The plastic reservoir can be removed. Once doing that you can inspect it and see what is needed. There is a good video out on youtube where the guy gets it all the way apart. You just have to work the reservoir off a bit at a time so as not to damage it.

[Larrym]

Anyone know what O-ring I need to replace that seal?

No...I don't know. （´＿｀）

But I do know a way to find out. (⌒_⌒)

I had the same problem with my front MC. Wasn't on XS11.club at the time so.......




Had to go back to my highschool days of mechanical drafting. Made basic drawings of both MC and resevoir. Measurements taken with digital calipers. Then High school math again to figure out what "space" needed to be filled by O-ring. Added 1/2 mm fOar the squeeze factor. ﾍ(￣ー￣)ﾉ

Ended up ordering the right size online at O-rings and more. (~‾⌣‾)~

Just saying, Mr GreyBeast....iffin' yur in uncharted territory and no one here knows the right size? ┐(‘～`)┌

Still not an unsolvable problem.... ( ಠ‿<)

[OldGreyBeast]

Man I failed remedial math twice in college, they eventually just gave me a D so I could graduate, lol. I could probably get close but I'd definitely defer to an expert XD

[Larrym]

I hear you, would be SO noice if yur call out to the ether gets some one to chime in with wut O-ring THEY bought/used. ヽ(•‿•)ノ

Still... when ordering online? Need only 2 (two) pieces of info- the diameter and the "cross-section" you want.

Diameter easily determined by taking the measurement(s) of inner/outer surfaces the O-ring will seat against, subtraction to find the difference between them, and then dividing that in half. I mean that's where's the O-ring is gonna ride, right? Smack in the middle between the two surfaces. ┐(°,ʖ°)┌

Cross section of the O-ring (how FAT/Plump it needs to be...) is just that difference/subtraction between the inner/outer surfaces distances.

Like mentioned before, With measurements made by a harbor freight digital caliper I was able to "do-the-math" and came up with the O-ring dimensions (diameter/cross-section) fOaR wut everybody sez was the right one anyways. (^_^)

The EPDM vs NITRILE vs wutever??? ( ´･_･`)

That's discussion is still ongoing and 'bout as useful as the oil or tire threads here on the site... ¯\_(°╭╮°)_/¯

[OldGreyBeast]

Oh nice, with the formulas I should be able to work that out. It's extrapolating the formulas from what was written down that I was like ...dafuq?

[Larrym]

It's extrapolating the formulas from what was written down that I was like ...dafuq?

Well....yeah. Yur right, Mr. GreyBeast. （◞‸◟）

Definitely mOaR than just a bit comfusing iffin' one is looking at the drawings/worksheet I did. ( ⚆ _ ⚆ )

But the worksheet wasn't just to figure out wut O-ring I needed. (　◜◡‾)

At the time I was also getting the measurements I needed fOaR the photorealistic 3D computer model of the reservoir/MC currently "in the queue" to be processed. ( º﹃º )

The system I use gets the computer model size/shape/accuracy within .2 mm (point two of a millimeter). That's like....the width of the line made by a sharpened #2 Ticonderoga Pencil. (⌒ー⌒)

But It's always bestest to get real wurld measurement(s) as a reference fOaR the model so's the worksheet got's em. ( ・_・)

Again....yur right. WAY overkill iffin' somebody just wants to figure out wut O-ring to order. My Bad. (ｏ´_｀ｏ)

[Ccitis]

When my front master was leaking I carefully popped the reservoir off, cleaned up all the gunk... and took the old O ring to the auto parts store and they matched it for me. It is nitrile, and there is all sorts of talk about that lol but its held up so far.

[OldGreyBeast]

It was pretty sketchy, but I was able to pry the reservoir off the rear MC. It seems to be 44mm ID x 2.5mm thickness. Mine measures 43.8mm ID 2.2mm thickness. Had to order a 50 pack from McMaster, so if anyone needs one... I've got em lol.