Ross’ 1975 CB750

[Galactica]

I think I got something installed incorrectly.  Gonna take it apart.

[Twisted_Twin]

If you can see the bottom of the reservoir, there is a little hole there that lets fluid into the mc. Check to be sure the holes are clear.

[kilowop]

With older machinery, when in doubt, use a larger hammer.  Might not work, but tends to vent the frustration.

[Galactica]

The holes were free from the get go.  Not frustrated enough yet to use a hammer.

The calliper was pooched so I replaced it with an aftermarket unit from Dave Silver Spares.  Replaced hoses I got from PartNMore/Vintage CB750.  I reasoned that the master cylinder was probably ok and decided to save money.  Then I realized the pressure switch needed replacing and it wouldn’t pump up firm with the new parts.  Ordered switch and master cylinder kit.  Got them yesterday but installed the master kit incorrectly.  Dismantled it and corrected it.  The new switch works better.  The system is filling now and I’m working on getting the air out.  It’s still soft.  I leave alone for a while and come back to it periodically.  Each time, I get a tiny bit more air out at the master.  I have the master tilted so that air cannot hide at the banjo.

[Galactica]

I don’t seem to be getting any more air but the lever still seems soft.  I’ll give it overnight and check for air tomorrow.

[Galactica]

So after all of that, the brake still seems soft.  I’m quite certain I have all of the air out of the system.  I’ll have to ride it to see if breaking is satisfactory.  At least the new break light switch works.

[Bucko]

I've always found air trapped in two places:

  * At the corners of the banjo bolts - bolt bleeding can help with that.

  * In the Master cylinder bore.  With the bike on the side stand, setting the handlebars so that the rear of the reservoir is angled up as high as possible, pulling the clutch lever and let it snap back, helps pull bubbles back and out of the two MC ports - repeat until no bubbles comes out.

[Galactica]

The banjos were tilted such that I doubt air would be trapped there.  I had the master well tilted so air couldn’t be trapped there either.  Dunno.  It must be in the calliper I guess.  My neighbour has a Mityvac that I can borrow.  I’m out of fluid though.  In any case, I can’t ride it until I get this sorted.  I rode up and down the lane a couple more times and it barely stops. 

[Galactica]

At least having run it in the lane, I’ve determined that the gauges work.  Accuracy is yet to be determined.

[Bucko]

The banjos were tilted such that I doubt air would be trapped there. 

I should have been clearer:  Bubbles are sticky little bastards and get trapped in the threaded holes at the 'shoulders'  of the banjo bolts.  At some point Honda, and others, started 'countersinking' the holes in the ends of the banjo bolts to reduce the cross-sectional area where bubbles can get trapped.  Loosening the bolts slightly while compressing the brakes allows the trapped air to be expelled, along with some fluid, past the threads.     The countersinking is evident in the attached picture of an aftermarket banjo bolt.

Those bubbles also stick in all the various corners inside a freshly filled master cylinder, and that's where the lever snapping can shake them loose.

[Galactica]

Where’s a place locally where I can get some banjo bolts?

[Galactica]

A quick google search shows mostly regular non countersunk bolts.

[fffCycles]

I dropped in to a Volkswagen dealership for my last purchase but they were very insistent I had to have a part number and they did not even know what a Banjo bolt was. First ones were wrong thread (1.25 vs 1.5 tip) then I figured it out and got and got another set. They were around $6-7 each.
Frank

[Galactica]

Honestly, I have a hard time believing it’s banjo bolts.  They’re exactly the same as my Kawasakis.  Basically the exact same system.  I never had trouble like this with them.  I’ve bled this thing six ways from Sunday.  Pumped the calliper piston out a bit and pushed it back to bleed it.  I need a brake guru to give me some help.  

This morning I discovered a puddle of fuel under the bike.  Petcock is leaking.  Maybe just at the tank/rubber washer interface…I hope.  Took the opportunity though, to drain the tank and do some quantity measurements.  Once the fuel gets to the top of the petcock tube there’s 4.4 litres of reserve.  Then there’s still 1.5 litres remaining on the right hand side of the frame hump.  

[Bucko]

Where’s a place locally where I can get some banjo bolts?

I wouldn't replace them, I'd just 'bleed' at the banjo bole.  It can be a little messy, so you want to ensure paint is well protected.