Front brake master cylinder

[RobAch]

The master cylinder always seems to leak fluid and appears to show up of right where the plastic section comes in contact with the metal. Always thought that’s where the leak was but it looks incredibly tight. Is it possible the leaking fluid just rings the joint of the cylinder? That said, would it be best to replace the entire master cylinder with some type of universal replacement or install a rebuild kit? Any direction would be very much appreciated

Rob

 

[xschris]

The plastic part pops off and there is an o-ring that seals it. Most times you can just clean it up and that will stop the leak.

 

[amc49]

Maybe................call it the pessimist in me. Brake fluid at some point picks up water to eat the aluminum, if inside o-ring groove looks like the outside casting you may have enough corrosion damage on the aluminum body to leak around the o-ring. It's one time fixable but you must plan on never pulling the plastic part again if done.

 

[RobAch]

So there is an o ring below the plastic body which comes off?

 

[xschris]

Yes it’s what seals the reservoir. It was a non-replacement part from Yamaha. But often leaks over time. The o-ring sometimes needs to be replaced. Just make sure to find one that can handle brake fluid.

 

[RobAch]

Thank you! This clearly was not meant to come off, easily anyway. So the plastic body is off and the o ring is removed. What a mess with corrosion. Hopefully I can get a new o ring at the local auto parts store.

Finally got the master cylinder plunger removed. All the parts I see though are not for a 1980 or are for a 650. Any good recommendations for parts? I checked a few older threads with no luck.

 

[xschris]

https://www.babbittsonline.com/oemparts/a/yam/50041ebef8700209bc786947/front-master-cylinder I think I have a full re-build kit new still in the package in one of my parts boxes. I will take a look and offer it up to you if you want.

 

[xschris]

Yep, I do have one. Genuine yamaha kit. $45 shipped.

 

[RobAch]

Done! Have a link for cc info?

 

[xschris]

I only take paypal.

 

[RobAch]

Currently I don’t have a paypal account but feel free to pass along a link. I’d be glad to try to sign up.

 

[xschris]

When you setup an account I will send you my paypal info.

 

[amc49]

Just me thinking aloud but I would be honing that cylinder out first before buying anything. If the corrosion does not clear up new parts may be a waste of time. If the corrosion leaves a deep spot then every time you activate the cylinder the piston seal will squirm off into the pits of the low and slowly tear the edges out to not seal.

 

[RobAch]

Thanks. Greatly appreciate the thought. The looks like there is very little corrosion inside the cylinder. Hoping new parts will do the trick.

I’m the now the proud owner of a paypal account

 

[xschris]

P.m. sent

 

[amc49]

Hold the MC body up to strong sunlight to view it, the bad spot is usually on the bottom where water tends to collect.

I typically use a made up hone as cars ones are too big. Take a piece of 1/4"-20 stud 4-5 inches long and cut a slot in the end with a hacksaw and then fold a piece of sandpaper ( I usually use #400) cut at about 2"x2" and fold it in half and in half again the same way with the abrasive facing out and then work the folded up piece into the slot you cut to create a flapper hone driven by a drill. Perfect for honing a bike MC. Use lots of oil mixed with a slight amount of solvent in it to lift the honing grunge away.

 

[RobAch]

With the master cylinder rebuilt and installed in the order of the photo, there is very little pressure when squeezing the front brake handle. It does seem to weakly stop the free spinning front wheel but would seem to unlikely to stop the moving bike. The front caliper was also disassembled, cleaned and returned and the brake fluid was added by pushing it in backwards from the caliper up to the MC. Did I mess up the MC rebuild? Any thoughts would be appreciated.

 

[xschris]

Did you bleed the system? You need to in order to remove all the air from it.

 

[RobAch]

Pulled the banjo from the MC to test. Boat loads of residual air. Front brakes now working great!

brakes, when stopping is even better than going!

 

[xschris]

You should bleed them from the bleed fitting on the brake caliper.