Brake Issue on Cali build?

[Bpreynolds2]

Hey all, I added another disc and caliper to the front wheel on my Cali Stone project.  I got a used, larger master cylinder from Ed (Guzzi Power) that was previously attached to a V11 Sport.  I acquired two used but seemingly fine braided steel lines of a different Guzzi with a double banjo bolt and copper spacers at the MC.  I installed 4 brand new pads for both calipers.  The whole system was empty and I primed and bled as per usual, or at least I thought.  When bleeding I see no visible air in fluid coming out of the bleeder on either caliper and in the past this is “usually” when the lever starts to firm up; however, it’s still pulling without any resistance all the way back to the throttle handle and behaving as if there IS air in the system.  The pistons on the calipers seem to have moved inward at least to the point of pressing the pads to the discs. What could be going wrong?  Again, there is absolutely no visible air coming out of the bleeder screws and I can’t discern a leak anywhere.  I’ve zip tied the lever and will check it again in about 8 or 10 hours; yet, I’m wondering if I should have better investigated that master cylinder.  Could it be at fault or causing this symptom?  While I’ve bled many a caliper, I’ve never investigated much into how a MC works or how it might be defective.  From research I see you can bench test the MC before installation.  Wish I had tried that, but then again, maybe MC is not the issue?

[bmc5733946]

You might try tying the lever back overnight, sometimes it allows air to rise to the mastercylinder, I have used a banjo bolt with a bleeder at the mastercylinder. You could block the pads in the calipers from moving and make the caliper bleeders the high point in the system. You can force brake fluid through the bleeders with a cattle syringe, many methods. I'd tye the lever back overnight and see what happens. Smacking the calipers sharply with a hard object can help break bubbles loose that get stuck in the corners of the calipers.

Brian

[yogidozer]

Like bmc said, You can force brake fluid through the bleeders with a cattle syringe, many methods.

[RinkRat II]

    Sounds as though the master cylinder piston is not returning all the way. Loosen the banjo fitting slightly and run the lever through several cycles to determine full flow. My $.02

        Paul B

[krglorioso]

Blocked return hole in the master cylinder fluid reservoir?

[Huzo]

Fill the m/c and lightly loosen the banjo at the handlebar end.
Actuate the lever and see if there’s fluid producing at that end. If so, do the same at the calipers. As mentioned, make sure the piston in the m/c is retracting far enough to expose the feed hole.
You’ll see some evidence of correct function, if when you let the lever out, a small amount of fluid surges back up into the reservoir.

It can’t be much.

[guzzisteve]

Could be that the used master needs a rebuild! This is why I bought a power bleeder runs on air compressor. The holes in the calipers that have 2 pistons side by side have very small holes in them and need more suction. My experience from bleeding this stuff on a daily basis for years. I used a hand pump for years. You can get them cheap.

[Bpreynolds2]

This morning I cut the zip tie and after about 16 hours of having it remain pulled, it is now showing resistance and not going all the way back to the handle.  I guess I did have some air in the line; yet, the lever still somewhat feels like a line with air in it somewhere as it is traveling further than it was even with the smaller cylinder and worn brake pads.  I thought if you went to a larger MC there is less travel in the handle?  Or maybe there is still air somewhere in the line I haven't removed?  Thoughts? 

[RinkRat II]

       Progress! Sounds like the probability of air still exists. Reverse bleeding been tried?  Just an FYI here's a handy little chart for M/C sizing and the differences you get

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

        Paul B

[bmc5733946]

I think that it is very hard to estimate braking power based on lever pull with a stationary bike. What feels kind of weak may land us on our noses while riding. I would ride it gen tly and see, if there is adequate braking, maybe ride it awhile then rebleed.

Brian

[John Croucher]

What size master cylinder do you have?  The piston may be too small.  This will make the lever feel soft/mushy/squishy.  The brakes will work and stop the bike.  If the piston is to large, the lever will fill hard/wooden, firm. But you will not have very good stopping power.  You will need to calculate the proper caliper piston size and quantity to master cylinder ratio to reach the type of brake feel you desire.  Your problem most likely is not bubbles, it is ratio. 

Here is a great place to start.

 https://vintagebrake.com/index.html

ttps://vintagebrake.com/mastercylinder.htm