Topic: radial master cylinder issues

[yodagruv]

I'm posting here since this is not a stock master cylinder, seems appropriate.

I've installed a radial master from a 2006 suzuki GSXR on my 75 CB550 with a dual front disc conversion (basically double-stock discs.) I know there's no air in the lines, I vacuumed fresh fluid through the entire system from the master bleeder out the calipers. I have no lever pressure and it seems that nothing is being pulled from the reservoir. I've pulled the MC apart and cleaned it all out (pretty clean to begin with) and there's no crud blocking anything.

theoretically this MC should push two cylinders easily since I think the oem calipers it pushes have 8. i had an MC from a 2000 ST1100 on it previously and it worked fine, just didnt work with my clipon setup.  any suggestions?

[MCRider]

Assuming that you know for a fact that the master cylinder is a functioning unit...

Its easy to think you have no air in the system, when in fact you do. Having just gone thru this with my project, i know how frustratiing it can be. i hooked a mitey vac up and everything. Was pulling fluid thru like it was full.

But there had to have been a bubble that was letting fluid pass it, but not coming out with the fluid.

In my case CB750 with an "over the fender" routing, i had to remove one caliper and hold it up while bleeding. After about 4 pumps, it burped several times and then got firm.

If the MC is OK, then there must be air in the system. Its not rocket surgery.

[fang]

I would agree that it sounds like air. +1 this can be frustrating!  That MC should work -- and even if it doesn't you should at least get a good hard lever before you know that it doesn't.  I am not sure this question belongs in the Performance Forum, but that's not my decision!

  I would start by bench flushing the MC one more time.  I sometimes am amazed at how persistent those bubbles can be in there.   

Once you are CERTAIN it is 100% air-free (and you have the banjo end capped and waiting for the hose hook up), then you might seriously consider reverse bleeding the system -- forcing the fluid from the bottom up and out through the top.  Bubbles like moving up more than they like moving down.  While you have the master cylinder removed to bench flush it, go ahead and rig up a brake fluid pump to the bleeder valve, and work the fluid up and out through the hose at the top.   Remember that after the master is bench prepped, regardless of how you flush the lines, it usually helps to start with the caliper piston(s) fully compressed while bleeding the rest of the system.

For your reverse flush you could use a giant syringe like Nurse GoodBody has whipped out on this poor lad:


 I also have a powered vacuum pump that I normally like to use.  It can suck a full reservoir down in a few moments.  It seems to help with stuff like this, but even then bubbles can get still stuck in an especially cantankerous system.  It seems better for replacing fluid than the original fill up/air flush.

Patience and persistence.

Good luck!
-fang

[yodagruv]

ok, I'll try bleeding again or force it up the other way...

I have been assuming this MC is good; let's say just for a moment that my only problem is that no fluid is being pulled from the reservoir. is it more likely that the piston needs a new o-ring? I can't get it to bleed from the MC bleeder using just the handle and no fluid is exiting the reservoir. there is no blockage in the MC/reservoir.

and sorry if this is not the place for this issue, I just figured the race/performance bunch would be more familiar with "Frankenstein" engineering like this.

[yodagruv]

btw, this is a 19mm MC

[MCRider]

Hmmm...If the MC is not drawing fluid and pushing it down the line, then I'd say it has an internal passageway that's plugged up. But I'm out of my comfort zone . Even if the system isn't firming up, dusto a hidden air bubble, you should still be drawing fluid from the reservoir and pushing it down the line. I think.

[fang]

I recently helped a buddy replace the clutch hydraulics on his late model Mini Cooper.  It should have been a quick job, but after spending too much time trying to bleed the system I still had no peddle pressure.  So I went back and bench bled the slave cylinder again, this time paying more attention to what I was doing, and PRESTO!  It magically all came back.

I felt dumb, but sometimes it really can be the simplest thing.

[turboguzzi]

the most efficient way i found to bleed is pulling vaccum from the caliper bleeders through a separator bottle, just remember to keep the reservoir always full.

if no fluid comes out from the bleeders then you have a block somewhere, simple.

another good tip is to have the pisotns pushed all the way in to minimize amount of air in the system.

have my doubts about a 19mm MC with the honda calipers,
common diameters in sohc dual discs setups are 14mm - 5/8" (16mm). unless the radial MC has a radically different mechanical leverage ratio, it might feel pretty wooden at the end of the day.

[jaguar]

http://www.vintagebrake.com/mastercylinder.htm

Yeah I would have to assume that the 19mm master will never work well with the brakes, even if the system is 100% right

[fang]

http://www.vintagebrake.com/mastercylinder.htm

Yeah I would have to assume that the 19mm master will never work well with the brakes, even if the system is 100% right

Jaguar,  That's a great link.  I often have wanted to see a chart showing brake caliper to master ratios similar to what you just provided.  Thank you!
-Fang