Topic: Dual disc troubles

[Coulisnosaj]

I have a CB750k3 with dual CB500 rotors and calipers, GL1000 master cylinder, and SB lines. I can’t seem to get the squishiness out to the lever, to save my life.  I bled the brakes several times; crack the joints to make sure there wasn’t trapped air, and then re-bled again and again, that didn’t seem to help.

I thought maybe the original CB750 splitter/divider AKA “T” wasn’t distributing the brake fluid evenly. I disconnection one of the lines and that seem to work much better, there was more firmness in the lever with only one brake. So I bought a GL1000 T, thinking that would be the fix (since it was designed with dual brakes in mind ) after installing and bleeding again and again, it was even worst than the original. 

So before I drop some more cash on a brand new GL1000 master cylinder, I’d like someone to tell me if I’m missing something or is the master cylinder the real culprit in this whole debacle.  All the best and thanks in advance!

[Hush]

You don't say how long the system had been rearranged, has it worked for you well in the past or did you add the 550 duals and now it goes squishy on you?
Without liquid flowing from the disc calipers at the wheel area you would have to think there is some sort of failure in the splitter valve where two become one, that would explain the reason when you disconnected one side it felt better.
My guess is that the seals inside the splitter are coozed, replace and should be all good.....just my thoughts...Hush.

[low-side]

The GL1000 master cylinder has a 5/8" piston, which will make the system work great.  I bought a used one on Ebay and a rebuild kit and reservoir kit from Parts N More.  Why did you use CB500 rotors and calipers?  The larger rotors from the 750 would give better stopping power and you can pick that stuff up cheap on Ebay and in junkyards.  Just a thought.  Good luck with it. 

[bwaller]

If the master cylinder isn't leaking while you're attempting to bleed I would leave it alone for now. You still have air in the system. Do you have speedbleeders? They are great and help make a one person job of this mess!

You mention you cracked the banjo bolts to release air? When you do this you need to release and tighten again the bolt the same as you would the bleeder valve at the caliper while you pump up the lever. You are bleeding the system at that point, otherwise it just allows air into the system.

First things first, try to orient the handlebars/front-end & brake lines so that any trapped air in the calipers will naturally find its way up to the master cylinder. No loops in the lines for example. Then just "tickle" the lever and watch inside the resevoir for air to appear. Experiment with how much little you need to pull the lever to produce air. Take a break now & then to allow air to work it's way to the top on its own.

This will help fill the lines and evacuate most of the air, and now if you have those speedbleeders you can finish the job and really produce a firm lever by giving it a quick bleeding at both calipers at once. A this point it will also become evident if the master cylinder is a culprit if it won't "finish bleed"

I wondered why the 500 rotors as well.

Good luck

[low-side]

Good advice on the bleeding techniques, I suggested the GL1000 master because it really finishes off the system.  When I had mine set up the first time, it took a fist full of lever to stop and felt worse than with 1 rotor.  When I added the freshly rebuilt GL1000 master it took one finger to stop.  A mityvac is also a good tool to have when bleeding brakes.

[XN]

What kind of bars do you have? If you have clubmans or a set that the master is installed at an angle with the banjo being higher you can get trapped air in the banjo that you will never get out.

Sounds like air in the system to me. Speed bleeders and a mighty vac will help. I would also go back and forth and bleed each side a few times brake fluid is cheap.