Clutch master cylinder rebuild

[BlackHawk84]

Hello Everyone,
I am new here and I hope to benefit from the combined knowledge of the group.  I have an '84 CB700SC and the clutch master cylinder is right at the maximum wear limit (as per Honda manual).  I have installed new piston kit this spring, and was able to get almost a full season of riding out of the old girl.  However, the MC is leaking brake fluid, especially on the hot days (my guess it expands a bit more).  Couple weeks ago my reservoir was almost bone dry.  Does anyone have any experience with re-building the MC in order to reduce the ID of the master cylinder?  is it possible to put an insert of some kind?  Is there a different piston kit with slightly larger rubber seals that will work?  Any advise would be appreciated.  Thanks.

[ERAU-944]

when you say it is leaking, i imagine that it is leaking from the cup that the lever pushes on, not out the top cap, sight glass, or hose fitting.

i redid the brake master cylinder on my first bike, a '78 Yamaha XS750SE.  the problem with mine was a bunch of pitting in the cylinder, so what i did was take it to a machine shop, had them actually remove some material, and then press a brass insert (he happened to have some brass piping the correct size in the shop) into the cylinder.  he then drilled the hole for the fluid through the top where the reservoir is so that the fluid would actually make it into the cylinder.  i lubed everything with new brake fluid, installed the rebuild kit, and it worked fine for over a year, then i sold the bike.

my advice is to take the MC apart (the seals are probably still good), and find a machine shop in your area and see if they will do something like this for you.  you will want to bring them the original specs for the MC, and see what they can do.  i paid $50 i think to get this done, but that was five years ago.  of course, machine shops in your area may charge more or less than that...

good luck!

PS.  Welcome to the forum!

[BlackHawk84]

Yes, it is leaking through the piston area, not anywhere else.  I was thinking along the lines or putting an insert in the MC but  I was not sure if it is doable.  Glad to hear it was done before  .  Thanks for suggestion.

[ERAU-944]

You are welcome, I just hope there is a shop near you with the skills and materials to get the job done!

[fishmeister]

http://cgi.ebay.com/ebaymotors/1986-Honda-CB700-nighthawk-S-Hydraulic-clutch-Lever-_W0QQcmdZViewItemQQhashZitem41527b5558QQitemZ280556688728QQptZMotorcyclesQ5fPartsQ5fAccessories


http://cgi.ebay.com/ebaymotors/84-HONDA-CB700-CB-700-SC-CLUTCH-MASTER-CYLINDER-LEVER-_W0QQcmdZViewItemQQhashZitem1c13f9aaa8QQitemZ120594213544QQptZMotorcyclesQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/1984-Honda-CB700-CB-700-Nighthawk-SC-clutch-system-_W0QQcmdZViewItemQQhashZitem2309c9899fQQitemZ150488058271QQptZMotorcyclesQ5fPartsQ5fAccessories

[ERAU-944]

i agree, i forgot the obvious option of a 'used' master cylinder.  i got a bit caught up in answering the question you were asking, as opposed to suggesting something a bit more realistic!

the dicey part is that there is no guarantee that the used master cylinder you purchase will be within spec either, but it is likely that it will be.

[BlackHawk84]

Getting a used one off the e-bay if an obvious option.  The only problem is you do not know what you are getting    You may score or you may miss.  I had good experiences with some parts and not so good with others.  My concern is that MC of the e-bay might be in the same condition as mine.  I guess it is always an option to get a spare one to have while rebuilding the old MC.

[Munkey]

Dennis Kirk has some aftermarket ones in their catalog. They are kinda pricey at $140 and frankly IMO, kinda ugly.  But, that is another option.