Front calipers are dragging - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 10-20-2011, 09:55 PM Thread Starter
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Front calipers are dragging

When I ride the front wheel felt like the brake was on so I put the bike (1993 Vulcan 750) on the centerstand and put a jack under the front part of the frame to lift the front wheel off the ground.

Yep the front wheel was dragging.

- first I bled the front brakes -- no change. Front wheel still dragging like the front brake isn't fully releasing.


- next I pulled both calipers and fully disassembled and cleaned them. THE DANG CALIPERS WERE PERT NEAR SPOTLESS INSIDE. I removed the 2 O-rings in each caliper anyways and cleaned the grooves, cleaned all the caliper bits inside and out (the puck, the caliper body and so on). Re-assembled and re-mounted the calipers and verified with the shop manual the calipers were correctly assembled.

Then I bled the front brakes.

NO DANG CHANGE the front wheel still drags like the front brake isn't releasing.

I don't get it -- what would be causing the piston (puck) in each caliper to remain engaged? IT'S NOT A SCORED PISTON OR BORE nor is it orings. Them things is all clean like a starving terrorist's feed plate his only meal for the day at Guantanamo. CLEAN not even bacteria on the innards of the caliper.


I'm thinking there is a 'return hole blockage' something I've heard about before but never experienced -- what does that mean 'return hole is blocked' and could that be the reason the brakes won't fully release?
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post #2 of 12 (permalink) Old 10-20-2011, 11:07 PM
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could be a blockage in the master cylinder not allowing fluid to return freely to the reservoir,or more likely either a brake hose deteriorating inside them and blocking fluid return.Since you say you have rebuilt the calipers, take it you did flush and fill the entire brake system with clean fresh fluid,if not,do it there may be moisture in the fluid.

These systems are notoriously hard to bleed,try pushing fluid back from the bottom with a syringe and watch for bubbles to come back up into the MC.

That should be enough to help you pinpoint the problem,one more thing make sure the calipers themselves can move freely and are not binding,good luck




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Last edited by denny6006; 10-21-2011 at 12:23 AM.
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post #3 of 12 (permalink) Old 10-21-2011, 12:10 AM
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If you rotate the front wheel for 360 degrees or more, do the brakes grab ALL the time or just PART of the time? If ALL of the time then x2 as Denny6006 suggests. If just PART of the time, its time to drag out the dial indicator and check for warpage of the rotor disk.


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post #4 of 12 (permalink) Old 10-21-2011, 01:09 AM
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Uh, how much are the pads "dragging"? (calipers do not touch the rotor, the brake pads do)

Can you spin the wheel fairly easy with one hand , but can hear/feel the pads rubbing on the rotor? Or does the wheel stop quickly when you try spinning the wheel fast by hand?

If it's the first one... a light but audible rubbing on the rotor, this is in fact normal. And you did all that work for nothing.

If it's the latter one, yes...make sure the rotors are not warped per OldHips post. Remove each caliper in turn to see if it's just one or both sides rubbing.

You might need to rebuild ( or replace ) the master cylinder.

So.... How severe is the dragging?

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post #5 of 12 (permalink) Old 10-21-2011, 04:52 AM Thread Starter
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Quote:
Originally Posted by denny6006 View Post
could be a blockage in the master cylinder not allowing fluid to return freely to the reservoir,or more likely either a brake hose deteriorating inside them and blocking fluid return.Since you say you have rebuilt the calipers, take it you did flush and fill the entire brake system with clean fresh fluid,if not,do it there may be moisture in the fluid.

These systems are notoriously hard to bleed,try pushing fluid back from the bottom with a syringe and watch for bubbles to come back up into the MC.

That should be enough to help you pinpoint the problem,one more thing make sure the calipers themselves can move freely and are not binding,good luck
I replaced all fluid with new brake fluid, system-wide. Only thing I did not do is disassemble and clean the m/c.

I do see bubbles coming back up into the m/c during the bleeding process but it was taking a LONG time to bleed them -- too long from my past experience with other bikes. I got a suspicion right there when I did not see a huge volume of bubbles coming back up into the m/c -- on other bikes after having the system wide open to re-do the calipers, there's usually a flood of bubbles coming back up into the m/c. On this one, just a few tiny bubbles every once in a while during the bleed process.

It was taking so long to bleed, I used a vacuum-speed-bleed attached to the bleed nipple on each caliper to hasten the bleeding process, to suck the brake fluid out of the m/c downward to the calipers. My vacuum speed-bleeding will go up to 30psi of suction. I do not think that air is the problem.

I am thinking it is your supposition of the blockage -- "blockage in the master cylinder not allowing fluid to return freely to the reservoir" -- so tomorrow I will yank and disassemble/clean the m/c with the intent on unplugging that blockage.

As to 'tightness' -- the tightness is consistent 360 degrees around the rotor and the pads have plenty of material on them. When I had the calipers apart, the pucks move quite freely in-and-out of the caliper bores so there is no binding there.

And when I installed the rubber o-rings in the caliper bores, and lubed the bore and orings with fresh Dot-3 brake fluid and went to install the pucks back in there -- I was able to do it with my thumbs and it was so dang easy compared to other calipers on other bikes I've done -- that experience was one of the grin-inducing part of my day. The pistons just got right back inside there with just the right amount of snugness. They're not binding.

The calipers are not releasing such that I have to pull hard with both hands to rotate the front wheel.

Normally, when you squeeze the front brake lever and brake fluid is pushed out of the m/c down to the caliper to push the puck out to the rotor -- when you then release the front brake lever, the big O-ring inside the caliper exerts a slight pull to pull the puck back away from the rotor -- and in so doing some brake fluid is pushed back out of the caliper bore back upward to the master cylinder.

In these disc brake systems, the big o-ring inside the caliper's bore will *not* normally pull the puck 100% clear of the rotor but will normally get it off the rotor enough so you can freely turn the wheel. Normally that big O-ring pulls the puck back into the caliper enough so that the brake pad will barely touch the rotor.

Since the big O-ring is fine, and the caliper bore is fine, and the puck is fine -- something is stopping the fluid from getting out of the caliper bore and returning back up into the m/c.

I cannot submerge the m/c in a bucket of cleaner and that tiny tiny return hole in the m/c is not accessible very easily -- what cleaning method will do me right on this one?

Obviously I will use my 120psi air gun. And I will have the m/c's piston and stuff removed from the m/c's body.

But what cleaning agent will open this apparently blocked tiny hole that I cannot get at directly with, say, a bobby pin to unblock it?

Last edited by CalifVulcan; 10-21-2011 at 05:03 AM.
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post #6 of 12 (permalink) Old 10-21-2011, 08:27 AM
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Quote:
Originally Posted by CalifVulcan View Post
I replaced all fluid with new brake fluid, system-wide. Only thing I did not do is disassemble and clean the m/c.

I do see bubbles coming back up into the m/c during the bleeding process but it was taking a LONG time to bleed them -- too long from my past experience with other bikes. I got a suspicion right there when I did not see a huge volume of bubbles coming back up into the m/c -- on other bikes after having the system wide open to re-do the calipers, there's usually a flood of bubbles coming back up into the m/c. On this one, just a few tiny bubbles every once in a while during the bleed process.

It was taking so long to bleed, I used a vacuum-speed-bleed attached to the bleed nipple on each caliper to hasten the bleeding process, to suck the brake fluid out of the m/c downward to the calipers. My vacuum speed-bleeding will go up to 30psi of suction. I do not think that air is the problem.

I am thinking it is your supposition of the blockage -- "blockage in the master cylinder not allowing fluid to return freely to the reservoir" -- so tomorrow I will yank and disassemble/clean the m/c with the intent on unplugging that blockage.

As to 'tightness' -- the tightness is consistent 360 degrees around the rotor and the pads have plenty of material on them. When I had the calipers apart, the pucks move quite freely in-and-out of the caliper bores so there is no binding there.

And when I installed the rubber o-rings in the caliper bores, and lubed the bore and orings with fresh Dot-3 brake fluid and went to install the pucks back in there -- I was able to do it with my thumbs and it was so dang easy compared to other calipers on other bikes I've done -- that experience was one of the grin-inducing part of my day. The pistons just got right back inside there with just the right amount of snugness. They're not binding.

The calipers are not releasing such that I have to pull hard with both hands to rotate the front wheel.

Normally, when you squeeze the front brake lever and brake fluid is pushed out of the m/c down to the caliper to push the puck out to the rotor -- when you then release the front brake lever, the big O-ring inside the caliper exerts a slight pull to pull the puck back away from the rotor -- and in so doing some brake fluid is pushed back out of the caliper bore back upward to the master cylinder.

In these disc brake systems, the big o-ring inside the caliper's bore will *not* normally pull the puck 100% clear of the rotor but will normally get it off the rotor enough so you can freely turn the wheel. Normally that big O-ring pulls the puck back into the caliper enough so that the brake pad will barely touch the rotor.

Since the big O-ring is fine, and the caliper bore is fine, and the puck is fine -- something is stopping the fluid from getting out of the caliper bore and returning back up into the m/c.

I cannot submerge the m/c in a bucket of cleaner and that tiny tiny return hole in the m/c is not accessible very easily -- what cleaning method will do me right on this one?

Obviously I will use my 120psi air gun. And I will have the m/c's piston and stuff removed from the m/c's body.

But what cleaning agent will open this apparently blocked tiny hole that I cannot get at directly with, say, a bobby pin to unblock it?
I had this problem myself on my 750,I actually took all the brake hoses off and blew them out with air and then used fresh fluid to wash them out.Don't forget to take off the manifold where the single line tees into the dual lines ,that ,with cleaning the MC out and maybe installing a rebuild kit while you have it apart,on the hard parts Brakleen would work but I don't think I would spray it through the lines .It may attack the rubber on the inside of them.Even after all this mine was hard to bleed,and continued to tighten up while riding.I carried a wrench in my pocket fro about a month and would open up a bleeder screw to relieve the pressure,after about a month it mysteriously quit dong this and I can't say definitely what was wrong with it to this day .I never saw any air come out, just fluid.That's why I said good luck, you will need it, along with a bit of patience.

Oh yeah, be sure to check out the return spring in the MC to make sure the piston is fully returning and that it is not partially blocking the return hole,once again good luck.




If you see it on my bike I did it
VROC#30324
92 vn750(sold)
Current ride 05 1500 Classic FI
lovin' the new scoot



Quote:
"When all is said and done,usually more is said than done" UNK
Click on one x and drag to the other to read between them.

Psalm 40:1...
XI waited patiently for the Lord; and he turned unto me, and heard my cry. X

Last edited by denny6006; 10-21-2011 at 08:31 AM.
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post #7 of 12 (permalink) Old 10-21-2011, 11:53 AM Thread Starter
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Quote:
Originally Posted by denny6006 View Post
".....make sure the piston is fully returning and that it is not partially blocking the return hole,once again good luck."
Thanks Denny -- question for you -- where exactly inside the master cylinder is the 'return hole' you mention? Is it inside the shaft where the m/c piston slides?
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post #8 of 12 (permalink) Old 10-21-2011, 06:09 PM Thread Starter
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Eureka I would say here, when I loosened the brake hose bolt on the master cylinder -- brake fluid shot out under some pressure (like the pucks in the calipers were trying to settle back into the caliper and pushing brake fluid back up to the master cylinder).

Then -- the front wheel got a LOT less sticky! I could easily rotate it with a medium-light touch of one hand.

Before I loosened that upper brake hose bolt at the m/c -- it took both hands and pulling hard on the wheel to move it at all.

So that told me the master cylinder was not allowing the caliper pistons to fall back into the caliper and push brake fluid out and up and back into the m/c. "Must be a blocked return hole" I thought.


I discovered a nearly-invisible 'return brake fluid hole' in the shaft of the master cylinder after I removed the master cylinder's piston and spring -- but finding that tiny tiny 'return hole' in the master cylinder almost did not happen.

It reminds me of having a nasty-ass zit back when I was a teenager and the gott-dang thing was plugged. The plug in the zit is so dang hard and crusty you want to drill it out -- like concrete.

Now imagine an electric guitar string thickness, I mean the thinnest string at the lower end of the guitar when you're playing it -- that's the 'high E' string on the guitar fyi -- the 'brake fluid return hole' in the master cylinder was not much thicker.

The plug inside was SO HARD, you could not see the hole inside the shaft of the m/c, at least initially. The hardened plug had been worn flat by the movement of the master cylinder piston -- you could not see the tiny hole there.

I had almost convinced myself 'there aint no return hole there at all'


Then I realized 'hey I haven't fixed anything then with this m/c and it will still be messed up when I re-install it.'

So there was a dimple inside the m/c bowl and I tried a bobby pin to see if there was a pinhole at the middle bottom of that dimple -- nothing.

I scraped away residue of old brake fluid in the dimple and then -- I saw what looked liked a tiny, plugged hole in the middle bottom of the dimple.

I play guitar and got 2 new strings out of my supply of strings: a .009 for the high 'E' string and a .014 for the 2nd 'B' string.

I grabbed the tip of the .009 guitar string with my needlenose pliers and tried to see if there WAS a hole by sticking the guitar string into the hole -- nothing. The guitar string would not go in. I bent the tip of the string 2 times and had to cut off the bent tip and kept trying to see if there was a hole by threading the guitar string into the dimple's center.

I almost gave up. Then I recalled plugged zits when I was a teenager.

I went back at the hole with my .009 and 'choked up' on the guitar string tip, by grasping the string with my needlenose at the very end of the string so only about 1/8 of an inch of the guitar string stuck out of the jaws of my needlenose -- I mean I choked up on that .009 string -- and gave that sucker HELL man, I got after it, I thought 'if there no hole then I will MAKE one' -- and then VOILA I broke through that plug and the guitar string slid through that tiny hole in the bottom of the m/c into the m/c piston shaft.

Then I pushed the .014 guitar string through it also and it REALLY opened up that hole.


So that folks was the problem -- that return hole had been plugged a LONG time. I'm headed out to re-intall the m/c, bleed it and will report back if that has fixed the sticking front brake, wish me luck. 'The high 'E' string in lieu of Clearasil on the master cylinder' trick I reckon.

Last edited by CalifVulcan; 10-21-2011 at 06:16 PM.
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post #9 of 12 (permalink) Old 10-21-2011, 09:46 PM Thread Starter
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Yep that did the trick, that little tiny return hole was blocked and it prevented my caliper pucks from retreating back into the caliper/away from the rotor when releasing the front brake lever.


It amazes me that such a tiny little hole have such a profound influence on this situation. Never underestimate a tiny hole is my takeaway on this.


Now that I can squeeze the front brake lever then feel the front wheel stop then release the brake and the front wheel spins again -- I set down to bleed the front brake system.

MAN OH MAN this is not an easy system to bleed is it.

I got it to the point where there is medium-strong resistance when I pull the brake lever in but I'm still feeling it as 'spongy' and my brake's strength is weak.

Is the Vulcan 750 known for being more challenging to bleed, I am wondering if the system design is such that -- either they needed to put a bigger master cylinder on it to make it push enough volume of brake fluid through the system or something.

I suspect I still have lots of air in the line and will re-do the bleed tomorrow -- HEY THANKS folks for the guidance -- I learned something new here -- if you could see how tiny the 'return hole' in the floor of the master cylinder is and how much affect it despite that size has you WOULD be amazed.
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post #10 of 12 (permalink) Old 10-21-2011, 10:26 PM
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It All Comes Down To 3 Things:
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Any One Fails - Then It Dont Run

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