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So the master cylinder for my front brake is leaking, just a bit. I fill it up with brake fluid and it takes about 3 weeks but the brake slowly starts to get mushy. I have looked and it is constantly moist under the actual cylinder and I cant find anywhere else that is leaking or wet so Im assuming its coming from there. My question is, should I replace the cylinder or rebuild it? I have heard a couple people say NOT to rebuild because it has to hold so much pressure that you don't want to mess with it. Has anyone done this? Do you guys have any recommendations? Also, does anyone have a spare master cylinder that they would be willing to sell or trade for something off my bike? I'm parting some things out like luggage rack, original handlebars and some other small things. I found a rebuild kit for like $30 but I'm not sure if its something that I should do or just try to find another one in good condition. Thanks for your help



Cody
 

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So the master cylinder for my front brake is leaking, just a bit. I fill it up with brake fluid and it takes about 3 weeks but the brake slowly starts to get mushy. I have looked and it is constantly moist under the actual cylinder and I cant find anywhere else that is leaking or wet so Im assuming its coming from there. My question is, should I replace the cylinder or rebuild it? I have heard a couple people say NOT to rebuild because it has to hold so much pressure that you don't want to mess with it. Has anyone done this? Do you guys have any recommendations? Also, does anyone have a spare master cylinder that they would be willing to sell or trade for something off my bike? I'm parting some things out like luggage rack, original handlebars and some other small things. I found a rebuild kit for like $30 but I'm not sure if its something that I should do or just try to find another one in good condition. Thanks for your help



Cody


Cody,



You might want to put the bike you have in your personal information. It can help us when giving advice.



I recommend rebuilding your MC unless when you tear it down you find that is pitted on the inside of the bore.
 

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Is there anything important to be looking for when searching for a replacement master cylinder?


Blindstitch got one and if you don't mind the wait or price(not too bad) you can get a near original round type(the best IMHO) from Wemoto over here,



http://www.wemoto.com/bikes/Honda/CX_500_A/79-80/picture/Front_Brake_Master_Cylinder/



Unlike the oblong ones they don't have screws so they can't get corroded in.





Check out the Customization section as well as the guys in there will have bought some.



These would work I reckon as well,



http://cgi.ebay.com/ebaymotors/NEW-...582336QQptZMotorsQ5fATVQ5fPartsQ5fAccessories





http://cgi.ebay.com/Universal-Hydra...orcycle_Parts_Accessories&hash=item33621c727e
 

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I went new too. Brakes are not something I want to screw with. Seriously, less hassle, more bling, probably better performance, almost definately more longevity. It was a no brainer for me, but I didn't care about the stock look. Think I "won" mine for $50.
 

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Is there anything important to be looking for when searching for a replacement master cylinder?



Math is a subject we all hate, but try to match cc displacement with what your caliper is designed for. Too far over and you may end up with a bit touchy system that can throw you over the bars in an emergency stop.
 

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Is there anything important to be looking for when searching for a replacement master cylinder?




Many of us have bought brand new replacement master cylinders from a guy down in Miami. He's got these in all sorts of finishes; I've posted black but my own is chromed and he's got other beyond that. The ads that he runs will list various motorcycles as if that's all they fit but the motorcycle doesn't have a clue what kind of MC you've mounted on it as long as it fits a 7/8" handlebar.



The piston diameter doesn't matter nearly as much as others have intimated. Certainly my replacement size was a little different than the original and yet my bike stops just fine with it with no bad habits apparent. Mine was supposedly for a Kawasaki bike.



USA-Motorcycles



Some of his ads have "buy me now" prices listed (generally $79.99 + $12 shipping) but you can always try to get one for less by going through the usual ebay bidding process. Several here have done that and gotten a real deal.



Here's a listing of his entire stock.



BTW, this would be the perfect time to swap out your brake line for a stainless one if you can swing the bucks. We have a preferred guy for that too.
 

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I'd go with a new MC.Why service a part that's around 30 years old when for not too much more you can have a nice new MC.



MY 10 penn'th.
I rebuilt mine and no problems. just my thoughts.
 

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So the master cylinder for my front brake is leaking, just a bit. I fill it up with brake fluid and it takes about 3 weeks but the brake slowly starts to get mushy. I have looked and it is constantly moist under the actual cylinder and I cant find anywhere else that is leaking or wet so Im assuming its coming from there. My question is, should I replace the cylinder or rebuild it? I have heard a couple people say NOT to rebuild because it has to hold so much pressure that you don't want to mess with it. Has anyone done this? Do you guys have any recommendations? Also, does anyone have a spare master cylinder that they would be willing to sell or trade for something off my bike? I'm parting some things out like luggage rack, original handlebars and some other small things. I found a rebuild kit for like $30 but I'm not sure if its something that I should do or just try to find another one in good condition. Thanks for your help



Cody


Busy rebuilding my 1980 Twin disk system, the whole lot.



The leaking you are seeing is between the plastic pot and the Master cylinder itself. What has happened is, with age, the brake fliud migrates past the seal under the pot and when it comes in contact with air, it crystilises. Then over time the breaks the seal and the brake fluid can then migrate dirctly out under pressure.



Removed the lid, drain and the with effort, you can pop the pot off, it clips into place, I slipped a screw driver between the M/C and the pot to pop it off, just be carefull, the wider plate you can use the better as the Alu and pot can damage easily....There will be a rubber seal in the master cylinder, remove and you'll see the crystals. Clean out PROPERLY, get a new seal and refit.



I just replaced my pot, seals caliper pistons, seals, all bought off eBay. It took me awhile to scrape out and clean the master cylinder and you'll be surprised how dirty it can be. Don't be shocked to see a kinda slim on the inside, if there is then you'll have to strip down the calipers because for SURE they have the same slim inside which rusts away the pistons, pits them and then they start to leak, old brake fluid due to poor maintenance.



I've redone the WHOLE system and fitting braided hosing to remove any flex from heat as the original pipes being 30 years old look good but add heat, they shot.
 

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I just rebuilt my front brake. Master as well as the caliper. Bled the brake line until all of the air bubbles were gone. The brake handle will not firm up. It is as though you are pumping a spring and that is it. I noticed that the MC bubbles when you pump it. Any thoughts? Could I have put the piston in backwards? I put the master in brake parts cleaner because it had a lot of the crystalized stuff in it. Also used synthetic fluid.
 

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I just rebuilt my front brake. Master as well as the caliper. Bled the brake line until all of the air bubbles were gone. The brake handle will not firm up. It is as though you are pumping a spring and that is it. I noticed that the MC bubbles when you pump it. Any thoughts? Could I have put the piston in backwards? I put the master in brake parts cleaner because it had a lot of the crystalized stuff in it. Also used synthetic fluid.


Click here,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=9&t=315





HTH
 

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OK. Maybe I had too much coffee this morning. This person is telling me to remove the banjo from the MC. Take the top off of the MC.(I have the one with four screws.) Top off the MC with fluid. Place the palm of my hand over the MC to form a "cover". Pump the handle until the fluid comes out of the hole where the Banjo was. Put the banjo back on and then put the cover back on. Is this correct?
 

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OK. Maybe I had too much coffee this morning. This person is telling me to remove the banjo from the MC. Take the top off of the MC.(I have the one with four screws.) Top off the MC with fluid. Place the palm of my hand over the MC to form a "cover". Pump the handle until the fluid comes out of the hole where the Banjo was. Put the banjo back on and then put the cover back on. Is this correct?


Nearly.



They are two different methods to achieve the same thing.You can place your hand over the MC top and press hard and then pump the lever slowly with the Calliper bleed nipple open but with a pipe on it submerged in brake fluid in a glass as I do or use a one-man brake bleeder.



If that fails then try the,"Banjo Bolt" method.
 

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Hi. I just spent a fair bit on my twin piston system. As with Trev2010 I rebuilt. My MC didn't leak but after 28 years service it looked like the reservoir was crazing and bulging. I sourced a cap seal and reservoir from EBay but from a USA vendor as it was cheaper even after shipping costs than buying from a UK vendor.



I'd go along with everything in Trev's post. The refurb went smoothly and the brake performance since has been way better.
 

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If you're still getting bubbles then the system isn't bled. A cheap suction bleeder is a good tool to have but that doesn't mean that it will solve your problem. Like I said earlier I have no luck rebuilding Master cylinders.
 

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Like I said earlier I have no luck rebuilding Master cylinders.


And, just to confuse the issue, I had the opposite experience than Don. I got a bad new MC from ebay so I then re-built the old Honda MC with K&L parts, no problems with the rebuild (other than putting it together backwards once, see next posting). Got my money back from the ebay seller.
 

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I noticed that the MC bubbles when you pump it. Any thoughts? Could I have put the piston in backwards?


It is possible to put the MC back together wrong and get bubbles as you describe. I know because I did it once.
 
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