Topic: Modern Master Cylinder won't work

[ev0lve]

Basically I'm posting this in case there's some bit of info I don't know that I should know I don't know. Or something.

75 CB750k converted to dual discs. I've had multiple MCs off of eBay from machines with dual calipers (Suzuki, Kawasaki and now Honda) and none have worked. This is my 3rd so far that I've hooked up and it won't move any fluid. I'm starting to think the problem is with me and not the MCs.

Sooo, I had the stock MC (rebuilt) on there and it worked OK but I've wanted to replace it with a modern and more compact MC thus the purchase of a 2000 CBR600 MC. I took the stocker off, hooked up the CBR - won't move any fluid. This is the same problem I had with an early 90s Katana MC (which I subsequently rebuilt and displayed the same issue.)

This little hydraulic system is about as simple as it gets. What am I missing that my stock MC works but every (used) MC I put on there is dead? Is it really possible I've gotten 3 duds in a row or is there some super secret late model MC modification I'm unaware of?

[Bill/BentON Racing]

Not sure but that M/C has no idea what its hooked to ,properly bled,should work,my race bike CB500/590cc Yosh has VF500F 85? m/c works well,different piston diameter.Bill

[Alan F.]

That's a tuff one, since your stock m/c works I'll rule out the brake lines being clogged.  If you were to take one of your ebay m/c's fill the reservoir and plug the outlet with your thumb while slowly stroking the lever, bubbles should rise from the reservoir on the return stroke and pressure should be slipping past your thumb blocking the outlet...(maybe place a clear plastic bag over it all to keep brake fluid from spraying everywhere)

I can't help but wonder about the banjo bolts you're using, are they compatible with the brake line you're using? Is the sideways hole in the banjo bolt being blocked by anything when you bolt it all together?  Are you using a single line to the m/c? or two lines on a double-banjo-bolt at the master?

[ev0lve]

I can't help but wonder about the banjo bolts you're using, are they compatible with the brake line you're using? Is the sideways hole in the banjo bolt being blocked by anything when you bolt it all together?  Are you using a single line to the m/c? or two lines on a double-banjo-bolt at the master?

Hmmm, please brain dump any info you have on brake lines. My impression was the banjo ends are all the same.

In this case it's the stock bolt that came with the CBR MC.

I'm running single line SS from the master to the stock splitter/pressure switch then two lines to the calipers.

[MRieck]

I can't help but wonder about the banjo bolts you're using, are they compatible with the brake line you're using? Is the sideways hole in the banjo bolt being blocked by anything when you bolt it all together?  Are you using a single line to the m/c? or two lines on a double-banjo-bolt at the master?

Hmmm, please brain dump any info you have on brake lines. My impression was the banjo ends are all the same.

In this case it's the stock bolt that came with the CBR MC.

I'm running single line SS from the master to the stock splitter/pressure switch then two lines to the calipers.

They are not....the bolt groove may be in the wrong place for your new master. Actually...it isn't groove placement it is the line banjo width were the bolt sits.

[Alan F.]

Give the bolt and washers from your stocker a try, be careful the first couple of squeezes of that brake lever as you could lock the wheel before you get used to the stopping power.  In all honesty you could probably lock the wheel easily at a panic stop, it's why some members shy away from upgrading too many parts in the front brake.

[ev0lve]

That would explain multiple failures. Is there a measurement or code I should be looking for to identify these. 10mmx1.0 or 1.25 (for a double) seems to be all there is (that I've seen).

For instance, what is the stock banjo and bolt if not 10mmx1.0? I can't find any reference to banjo ends in any other spec other than size of the lines

Stuff like
ALL50070    3/8"-24 Banjo Bolt   2 pack   $7.99   
ALL50072    7/16"-20 Banjo Bolt   2 pack   $7.99   
ERL977522    7/16"-24 Banjo Bolt (Includes 2 Crush Washers)   EACH   $5.19   
ALL50076    10mm x 1.25 Banjo Bolt   2 pack   $7.99   
ALL50077    10mm x 1.5 Banjo Bolt

and
ERL997603    Steel Fitting - 3/8" Banjo to -3AN   each   $7.79   
ALL50061    Steel Fitting - 3/8" Banjo to -4AN   2 pack   $12.99   
ALL50062    Steel Fitting - 7/16" Banjo to -3AN   2 pack   $12.99   
ALL50063    Steel Fitting - 7/16" Banjo to -4AN   2 pack   $12.99   
ERL997631    Steel Fitting - 10mm Banjo to -3AN

[Trav-i]

I had a simillar problem with my master after I rebuilt it.  What I had was an air pocket that I couldn't break.  So to brake the pocket I hooked up my vacuum gun to the master and pulled a vac with the handle held back.  After a few seconds I saw a little fluid in the cup, then pumped the lever a few times and got awesome fulid flow.  Broke the vac on it and now it pumps perfectly, I have done this twice with great results.

Hope this helps, good luck

Travis

[gerhed]

Might need to do a bench bleed with the MC just to get things moving properly.
--Put it in a vice --fill it up --pump it & suck it out--etc.--repeat.

[KCRSXTypeS]

When I rebuilt my stock MC It took about 10 min. of pumping it to get it to move any fluid...