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2001 Kawasaki Vulcan 750
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Discussion Starter #1
First the good news: My project bike is nearly 100%. Started up tonight for first time since I became the owner, and I went for a 25 mile test (joy) ride towards Santa Cruz, and she is sweeeeet!!!

But....I've done many brake jobs before, rebuilt master cylinders and the whole she-bang, but never ran up against such a stubborn one that is on my Vulcan.

Went through all the excellent forum posts and I'm out of tricks and patience.

First starting with Master Cylinder (MC). Was completely cleaned with isopropyl, compressed air, then BrakeCrafters rebuild kit and sparingly used RRG (red rubber grease). Bench tested it with single hose connected to the right caliper, which was also rebuilt. Felt weird, would not pump up. But using the thumb test, it felt fine. The local dealer mechanic charged me $60 to tell me it was fine too,

Replaced pitted piston in left caliper and replaced both the fluid and dust seals.

Used Mity-Vac to draw fluid thru both calipers, several times. Did the regular brake bleed method after that.

Never got any firm brake lever.

Tried a trick from another Vulcaner: Went to CVS and got a syringe, connected it to left brake bleeder with a hose, but when I opened the bleeder it pushed fluid out into the hose and could not force any more in.. so it seemed to have pressure there.

The only thing i noticed is that when I used the Mity-Vac on the left caliper with 15psi vacuum, and opened the bleeder, I got a solid stream of fluid into the bleeder hose.

On the right caliper, I got tons of bubbles. Always. So is the problem inside the right caliper? It was rebuilt the same as the left, and the seals and piston seemed just great on the bench. It is so simple, what could go wrong?

So I am losing sleep over this and can't bear the thought of bailing out and spending $120/hour at the local dealer.

Does anyone have any ideas how to locate and fix this problem before I throw in the towel (and checkbook)?
 

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Not sure what's going on.

Did you replace the hoses or use the same ones? Just thinking about collapsing hoses, but for some reason I was thinking you got braided brake hoses.

Did the right side ever stop producing bubbles? Continuous bubbles probably means a leak somewhere.

Did you try tying the brake lever back and letting it gravity bleed for some hours?

Any chance a rubber cup got installed backwards? Does the master make pressure?
 

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2001 Kawasaki Vulcan 750
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88 Posts
Discussion Starter #3
Not sure what's going on.

Did you replace the hoses or use the same ones? Just thinking about collapsing hoses, but for some reason I was thinking you got braided brake hoses.

Did the right side ever stop producing bubbles? Continuous bubbles probably means a leak somewhere.

Did you try tying the brake lever back and letting it gravity bleed for some hours?

Any chance a rubber cup got installed backwards? Does the master make pressure?
Let’s see...

I used the same hoses just soaked em in soapy water dried out with compressed air.

One post said those bubbles are just coming in thru the hose attached to bleeder valve. I’ll have to rest up and try again I’m no good at video but try to make one.

I’ll do that lever tie down thing today.

I compared that MC cup like four times. Will check my photos. It will push hard on my thumb. If I keep my thumb over the exit,the lever stays depressed. Is it supposed to snap back?

I’ll have to rest up and get over it being a messy job and get back to working on it.

Appreciate the help thinking this thru.
 

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Yes, the lever should have some spring action returning it to position. Not sure if it's possible, but the action you observed might mean the cups are reversed.
 

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2001 Kawasaki Vulcan 750
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88 Posts
Discussion Starter #6
Tie the brake lever all the way to handle bar. Fill the fluid reservoir and let set over night.
After one night I noticed a very slight improvement. Left it tied back more than 24 hours, and it felt even more better (good grammar, huh) and started to pump up. I'll leave it again overnight and then do normal bleed, and hope it keeps pressure but it looks promising at this stage. Mucho thanks.
 

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2001 Kawasaki Vulcan 750
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Discussion Starter #7
After one night I noticed a very slight improvement. Left it tied back more than 24 hours, and it felt even more better (good grammar, huh) and started to pump up. I'll leave it again overnight and then do normal bleed, and hope it keeps pressure but it looks promising at this stage. Mucho thanks.
UPDATE:
I can't understand it, but this worked like a miracle.

Tied back the lever two nights in a row. Got better both times, and now it not only pumps up, but holds pressure with lever only halfway to the bar, and I haven't even done any further bleeding!

I can't figure this out.. I had used Mity-Vac, bled the MC at the banjo bolt, bled each hose at the junction, even tried pumping fluid into the calipers with a syringe (didn't work, they had enough pressure that I couldnt pump anything into them).

This will make riding the Vulcan a lot safer than before. :):)
 

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I think the geometry of the brake master cylinder/reservoir has some oddities in it that make for small bubbles that don't flush out easily, and when you tie the lever back it leaves the intake from the reservoir into the cylinder open to the reservoir, allowing bubbles to rise to the top and out of the pressure side of the assembly.

Glad you got it working!
 

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2001 Kawasaki Vulcan 750
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Discussion Starter #9 (Edited)
I think the geometry of the brake master cylinder/reservoir has some oddities in it that make for small bubbles that don't flush out easily, and when you tie the lever back it leaves the intake from the reservoir into the cylinder open to the reservoir, allowing bubbles to rise to the top and out of the pressure side of the assembly.

Glad you got it working!
Never would have gotten this done without hearing about it here. Thank you to all you Vulcaners!

BTW ubertalldude your backrest looks rad thumbs up.
 

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Thanks! It's really simple. I got extended bolts with thumb-screw heads on them (great for tool-free removal of the seat) for the seat back (M6x1.0 thread, ~30mm long) and just used a spare piece of thin plywood to slip in between the seat and the backrest support. The bolts thread thru drilled holes in the board, and the backrest pad was a cheap one off ebay. Whole project cost about $25 if I were to buy all the parts new, but I had the plywood laying around.

I seldom have a passenger, but when I have they seemed to like the added support, and when I'm riding solo it's great for long trips since I can strap gear to it more securely than just strapping to the luggage rack.

I also mounted the helmet lock onto the board, that way I can rest my helmet on the backrest and lock it in place when I walk away from the bike.
 

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UPDATE:
I can't understand it, but this worked like a miracle.

Tied back the lever two nights in a row. Got better both times, and now it not only pumps up, but holds pressure with lever only halfway to the bar, and I haven't even done any further bleeding!

I can't figure this out.. I had used Mity-Vac, bled the MC at the banjo bolt, bled each hose at the junction, even tried pumping fluid into the calipers with a syringe (didn't work, they had enough pressure that I couldnt pump anything into them).

This will make riding the Vulcan a lot safer than before. :):)
Glad I was able to help. It slowly lets air to rise to the top and out of the system.
 

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2001 Kawasaki Vulcan 750
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Discussion Starter #12 (Edited)
Glad I was able to help. It slowly lets air to rise to the top and out of the system.
I've been busy doing other things so haven't done any further bleeding is that necessary? The brakes lever does not come back to the bar, but almost does, and is definitely mushy compared to what I am used to.

Stainless brake lines are such a ripoff over-priced, but I am wanting those. But even these rubber hoses should not be so freaking mushy. What a weird MC design that traps air and won't pump it thru the system.
 
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