Front Brake Master Cylinder Cap

[ajs350]

My front brake master cylinder cap was all faded so a bought a new one from Honda. After I installed it and put the handle bars in the left locked position the cap leaked. I tightened it a little more but it still leaked.
Replaced it with the old one and all is good. Do I just need to get a new rubber seal or should I have bought the full kit with resovoir, cap and seal?
Thanks
Ross

[FalldownPhil]

Check between the cap and rubber to be sure that the metal "thingy " is in place.

[daves79x]

Ross:

If your cup is at all distorted, it will probably leak with the new cap. I just gulp and buy the whole set. You can get the aftermarket ones and they are just fine. You will need to pay particular attention to the o-ring that seals the cup to the body - it has to be replaced and the groove cleaned well. The o-ring comes with the full kit.

Dave

[ajs350]

Check between the cap and rubber to be sure that the metal "thingy " is in place.

Good catch. I do not have one of those but found an old one in my box of bits. I'm going to clean it up and give it a try. Hopefully it will work but if not I'll have to cough up for the full kit as Dave suggests.

[ajs350]

Once I installed the diaphragm the leak was gone. Here's the before and after but as you can see it does not match the gauges so that will have to be next. Will it ever end?

[FalldownPhil]

Glad it helped. Every once in a while, I get lucky
I guess that means I will miss the next few
Best,
Phil

[mac.]

I have also decided to refurbish my front brake master cylinder. I managed to get replacements from Honda for all the parts excluding the cap, they originally said they could get the cap too and that's why I ordered them. Unfortunately they can't get the cap any longer. Buying from outside RSA is just too costly at the moment with the exchange rates. Anybody know of a local option, even good condition second hand?

Tx's

Mac

[hondaman160mph]

I am also replacing the front master cylinder reservoir and cap on my '82.
The cup was slightly bowed out and installing a new gasket didn't
stop the leak. I have an after market kit made by Tour Master made in Japan, cup, gasket, cover and o-ring. It looks identical to the stock one , what is the metal "thingy" Phil mentioned?
Also there is a small slot cut into each end of the cover which I assume are vents. What's to prevent brake fluid from leaking out there?

Jeff

[daves79x]

Pro-Link caps don't have the metal thing. Fluid won't leak out the vent slots if everything is installed correctly.

Dave

[Larry Zimmer]

For those who have not done this previously, that is replace the m/c reservoir/oring. a word of 'how-to'. To get the reservoir off the master cylinder, you just have to pry it out. The only thing holding it are the two screws through the cap and a snap fit. The snap fit is a barb arrangement with the oring into a groove in the m/c. It might take some serious prying to get it out. (Depends upon how long it's been there.) Working some brake fluid in around the seal joint and letting it soak might help ease disassembly. Just be a bit careful to not gouge the master cylinder. It's aluminium! As Dave mentioned, clean the groove in the m/c well. BUT, DON'T SCRATCH IT! Reassembly is easy: lube the oring and groove with brake fluid and 'pop' it together. Goes easily when lubed.
This applies to the prolink models. I can't speak for the 79/80.

[asacuta]

After fiddling with the master cylinder, and you are sure everything is buttoned up, wash the area liberally with water and dry with a bit of compressed air: you don't want drops of brake fluid to blow out on your next ride and land on your tank. Don't go crazy with the compressed air.

[mac.]

Whilst rummaging through the internet trying to find a cap for the master cycliner cup, I've come across quite a few places that offer the full refurbishment for the '79. But they all have 8 screws and I can't understand why? Mine only has 4.

Can someone please enlighten me.

Tx's

Mac

[FalldownPhil]

Sure, 4 screws are pan head and 4 are tapered for two different style caps.
Phil

[mac.]

Thank you Phil.

I've also decided to bite the bullet and get a new cap rather risk a second hand unit leaking brake fluid onto the tank while riding.