Topic: Popped Master cylinder boot trying to get it in

[juntjoo]

Do you gotta get a whole new rebuild kit to replace that boot? Anyone know if you can find that part somewhere by itself? Is it possible there are similar out there at maybe an ace hardware that would work? I'd like to be able to buy a could as it's so easy for me to tear these. I remember doing it through two rebuild packages in the past for a car. Call me clumsy but I don't do it on purpose, idk, I guess I am but I like working on stuff. I just wish little parts like these were easier to replace

[juntjoo]

http://m.ebay.com/itm/131695010111  hmm, wonder if this will work

[juntjoo]

Anyone have an idea where this "14mm" in the above link is measured? This looks pretty much like the correct boot no? But obviously it's got to be the right size.

[Bodi]

14mm is the master cylinder bore size. The OEM m/c was 14mm for single disk Honda fours.

[juntjoo]

Thanks! Real quick, bore size? Is that in length or diameter or...

And single disk? Like one disk on one side of the front wheel or.. (that doesn't make sense lol), sorry, new to this.

[Scott S]

This is exactly why I just pony up the $45 or so and get a brand new master cylinder from David Silver Spares.

[juntjoo]

Hmm... my problem is I underestimate the degree of care to do some of this work and I think 'oh easy fix let's gettir dun!' then I end up here.  I do it all the time, regardless of how simple it is and putting on these boots, if you do it a few times I'm sure is really easy but when I get in there for the first time on something that requires a little techniue/thinking I don't slow down and wiggle my way into breaking something.

I remember years ago after breaking so many rusty bolts on an old car I finally took the time to learn how to properly remove rusty bolts...

PATIENCE!

[juntjoo]

Unless I'm measuring wrong, mines almost 16mm. If I get one a little bigger to make sure the base is sealed, I run the risk the top part could be too loose. And if I get one a little smaller to ensure the top fits I run the risk the bottom is too loose and leaks. Any ideas?

[Scott S]

It doesn't look like your caliper is zeroed out on the "0" end.

Stock Honda master cylinders for the 500/550/750 are 14mm. I can't say if the eBay seal you posted will work or not.

[Scott S]

https://www.davidsilverspares.com/CB550F0-SUPER-SPORT-1975-USA/part_123899/

[juntjoo]

Thanks, but look again, it may not be "zero'd out" but it's aligned with the reading mark to left if you get what I'm saying, which is all that matters with this basic caliper. 

So interestingly the boot I punctured seemed to fit perfectly.  I bought if off ebay which didnt specify the bore size but said it was for my bike which I would imagine corresponds with the 14mm.

Anyway, here's a pic of some info.  Does this mean anything to anyone?
 

In the end I just may buy the same kit I got originally but then I'll end up with these perfectly brand new yet useless parts, most likely.  It's not even that much more than the individual boot.  Now I'm just curious why my bore doesn't measure 14mm. 

[juntjoo]

yeah, I see the 14mm.  I wonder if mine is a 16mm because maybe mine leaked not only because of the hole I poked but the 1mm gap around the bore my boot could've left.  And if that's the case, getting the same kit... come to think of it, putting that ring gasket around the piston was a b@%#! as if mine was 2 too many mm's wide.  So maybe I need to be searching for a boot for a 16mm MC.  $18 education. Not too bad.

[juntjoo]

No, I just re-checked and the old and new-punctured one fit nice and snug against the bore. For whatever reason mine measures 16mm seems like the 14mm boot is what I should get.

[Scott S]

Your master cylinder is clearly marked 5/8" which is 15.875 mm. The stock Honda master doesn't have the switch underneath like that either.
Show us an overall picture of the master you're trying to rebuild. What year and model bike?

[Scott S]

And why would you buy a 14mm master rebuild kit for a 16mm master cylinder? You should be looking for a 16mm or 5/8" kit.

[juntjoo]

hmm, I guess I didn't put two and two together.  My brain was still processing how MC's and their respective replacement parts are measured. Think I got it now.  And in mm's it's close enough if I don't find a 5/8 solution no?  Well I'll look hard for a 5/8 boot..