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Master cylinder return port

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G

Guest

Guest
I keep reading about the tiny return port in the master cylinder that must be cleaned and ensured open. I can't find any such port on my master cylinder (1981 650GL). Could someone post a pic so I know what I'm looking for?

Thanks.
K
 
From google...

Photo0073.jpg
 
Thanks Ed. I see the tiny hole but where in the master cylinder assembly is this?
 
Obviously, it's in the bottom of the reservoir. You will see the larger hole, it is toward the end of the handlebar. The smaller hole will be toward the center of the bike.

On some bikes, there may be a little tab of plastic from the reservoir that covers the hole. The only way to see that one is to pull the reservoir off. If you are going to the trouble of removing the reservoir, you may as well change the o-ring that seals it. Heck, you may as well just change out the whole reservoir.
icon_shrug.gif


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Or the whole Master Cylinder.

I just bought one including a rebuild kit for less than the Suzuki rebuild parts.
 
Last edited:
This is my front master cylinder. The reservoir has two holes, neither of which are tiny. I was looking for a tiny hole somewhere in my master cylinder so I could make sure it was unplugged. So it looks like the MC on the 1981 650GL differs from others. <insert "L-bashing" shot here> :D

 
The smaller of the two holes is the one. Some are smaller than others. That one is clean inside, did you do that or was it that way?
 
Is the bore clean and free of pitting of the metal? Lots of old masters are corrosion pitted because the brake fluid wasn't changed regularly.
 
Nessism said:
Is the bore clean and free of pitting of the metal?
Click to expand...

Yes, and surprisingly so. The fluid sat since at least 1992, and could possibly have been the original. I was expecting the worst when I opened everything up, judging by the colour and consistency of the fluid (think chunky coca cola). But there was no corrosion in the bores or on the pistons, and very little corrosion everywhere else. I'm confident that I cleaned out all the ports very well, but I'm going to double check before I reinstall the brake system. Just waiting to get my wheels back.
 
Just remember during reassembly use nothing but clean brake fluid.....

.
 
Well, I just want to say "Thank you!" to those who replied about the tiny return hole in the master cylinder. I assumed I had everything good and clean, but when I checked the front master cylinder I could not find that hole. So I poked and prodded and scraped and it finally revealed itself. It was plugged with such a small piece of crud that I couldn't even see it. I poked with a sewing needle, then a piece of wire from a wire brush and it's now clear. I took the MC apart and double checked everything. I also did the same for the rear and it was clear and clean already.

So again, thanks! You saved me, at the very least, another teardown after everything was assembled. Or worse if the breaks locked up on me!

Cheers!
K
 
You should tear down the calipers if you haven't already done so. Get new brake lines also. Crud builds up in the system and the only way to avoid troubles is maintenance.
 
Calipers are already done and I have new stainless steel brake lines ready to install.
 
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