Brake caliper rebuild dos and don'ts?

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NobleHops
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Brake caliper rebuild dos and don'ts?

Post by NobleHops »

I'm having a little trouble getting one front caliper to seal. After powdercoating the caliper, the (bare) inside of the bores felt a little toothy to me, so I wet-sanded them lightly with a little brake fluid, then cleaned them, then rebuilt with new K&L kits. Two of the three sealed fine, one will not, and like George Garrison with his Duc, it's spongy no matter how much I bleed it. It's no big volume, but a day after pumping them up, and scrupulously cleaning the caliper, I find a single brownish dot of brake fluid, that I think it has transited the seal in the borebased on where it's falling from.

I'm taking it apart tonight and have a new kit on standby. Any tips? My brother was suggesting I might have made the bore too smooth. Any opinions on that theory?

N.
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George R. Garrison #0857
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Post by George R. Garrison #0857 »

Nils, if you find a solution, let me know.

I tried bleeding the system in both directions and the pedals still soft.

I bleed two pints of fluid thru a system that holds maybe a 1/4 of a pint total. What am I missing?

The brake works, there's no leaks, the linings are almost new, the fluid is new, the disc is clean and smooth. The system consists of a fluid pump as Ducati calls it, and resevoir with connecting hose, the brake hose to the rear caliper and the caliper itself.

Good luck with yours.

Later, George in Delaware
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Post by Rick Pope »

A place where an air bubble might hide is the banjo bolt at the master cylinder. I had that happen once, and cured it by loosening the bolt just a bit, then squeezing the brake lever enough to force fluid out around the washers.

Just a thought..............

Something else to try is to remove the master from the handlebar, and tilt it so the head of the banjo bolt is down. (You might accomplish this by just turning the bars to the left.) Wiggle the lever and perhaps a bubble will find it's way to the resevoir.
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Post by TerryL »

Anyone ever use a hand massager/vibrator (anything that vibrates) on the lines down low during the bleeding process? I've heard it gets any bubbles from the wheel cylinders and lines 'agitated' enough to head for higher ground and out the top of the master cylinder.
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Brake air bubbles

Post by George R. Garrison #0857 »

I'm going to try cracking the bango fitting bolts and bleed some fluid.

Plus, I have tried shaking the lines and will try to find an earthquake to park over.

I just may try using a heat gun to warm things up a little to see if it helps. And maybe a hand held vibrator to see if she responds.

Thanks for all the idea's and I'll try them all.

Is anyone aware of a pressure pot rig for bleeding brakes, clutch's or other hydraulic components that are subject to air?

Thanks, Later, George in Delaware
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Post by EMS »

Nils: The walls of the bore don't actually seal against the piston. The seal does. I doubt (doubt!!! = don't know!!) that your sanding procedure did cause a problem. This may be elsewhere. These front dual brakes are a pain in the neck to bleed properly.

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Post by Jeff Bennetts »

One thing I like to do is use a slice of dirt bike inner tube( like a big rubber band) on the front brake lever, once the lever is pumped up with the band holding pressure on the lever I tap all the lines and let it sit over night with the band on, then bleed the system again.

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Post by daves79x »

Duct tape works as well to hold the lever back. Nils - I doubt that the caliper is your problem. Everyone has problems bleeding these front brakes. Here's what I have found works most of the time:

Remove the calipers and splitter as one unit, then fish the single hose from behing the headlight (you have to remove the right headlight mounting bolt). Work the calipers up between the forks and fashion a table about handlebar-high to lay everything on. Your master cylinder is still connected to the bars.

Now you have everything sort of level. Bleed out the calipers with a vacuum bleeder while rotating them in your hand and wiggling the lines. You will be amazed at the air still trapped in the calipers and lines. With everything level - the air goes where it is sucked to and you are not fighting 3 feet of gravity. This is why the rear system is so easy to bleed - everything is about level.

This has worked most times for me better than anything else - and I've had lots of these systems apart. It is not as much of a pain as it sounds. Also, grab an old rotor or something about that thickness to stick between your brake pads to test your lever pressure while the whole thing is still on your table.

Dave

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Post by daves79x »

Also forgot to mention that you have to use teflon tape on the bleeder threads if you are going to use the vacuum bleeder. It'll suck all sorts of air through the threads if you don't. Some guys smear grease around the threads and that works but it's messy.

Dave

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Post by SteveG »

What has been said above are all excellent tips.

I have had good luck with a Mity-Vac brake bleeder, and the quart size jug of brake fluid. Keep sucking the fluid through, making sure you don't drop the level in the the reservoir so far as to suck air. Check pressure every now and then, and eventually you end up with a hard handle.

If frustration sets in, tape/band the handle back for a while and maybe attach a vibrating mechanism to the lines / splitter and get some more beer while you wait.

Or keep the reservoir - lines - calipers all on the same level like Dave said, or even raise the calipers (bleeder nipple to the top) above the whole mess.

Any single or combination method will eventually free up that last air bubble stuck in the corner that gives the spongy lever.

As far as the brake fluid drip hanging, that could be just the remaining moisture from assembly consolidating where gravity takes it. If you get good pressure, and the drip doesn't reappear, don't worry about it. (But keep an eye on that area like you will all other potential leak points). :D

Steve

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Wow

Post by NobleHops »

Great stuff guys, thanks.

I rebuilt that caliper again, as it WAS leaking through the piston/seal area. There is one good pit near where the piston would transit the seal repeatedly. If it leaks again I will replace the piston, though for now it is holding fluid.

I will try the bleeding techniques described - it occurred to me to use a palm sander as my vibrator (sans sandpaper natch). It's out there on it's sidestand at the moment with a velcro strap holding the lever 2/3 to the bars. I'll report back after I have a chance to try this all.

Thanks again,

N.
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Re: Wow

Post by NobleHops »

NilsMenten wrote:Great stuff guys, thanks.

I rebuilt that caliper again, as it WAS leaking through the piston/seal area. There is one good pit near where the piston would transit the seal repeatedly. If it leaks again I will replace the piston, though for now it is holding fluid.

I will try the bleeding techniques described - it occurred to me to use a palm sander as my vibrator (sans sandpaper natch). It's out there on it's sidestand at the moment with a velcro strap holding the lever 2/3 to the bars. I'll report back after I have a chance to try this all.

Thanks again,

N.
OK, the whole system is off the bike and laid out horizontally, the MC is clamped in the vice on my lift and the calipers were repeatedly bled. I'm going to hang then before I leave for work and then bleed them one more time off the bike, then reinstall. Being able to rotate the calipers and the splitter fitting, plus tapping on the brake lines yielded a LOT of bubbles. I can't imagine how I'd ever get these bled on the bike as I was trying to do it. Thanks for the suggestions.

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

(sorry no quoting for context, we're working on it)

Update on my brakes is that my MC was leaking, so I took it back apart and dremel-wire-wheeled some stray powdercoat and powdery corrosion from the area near the circlip groove, and cleaned it all scrupulously, dried it and then re-rebuilt it. I hung the calipers higher than the m/c, re-bled the system, waited a few hours, bled it again till I got no more air, and it's pretty much there: I can't get it to the grip and it seems about as hard as my other bikes' levers. If that MC springs another leak I will ditch it and investigate those alternatives.

Dave McMunn, what would you say is performance comparison between the stock CBX and 2-piston 900F brakes? IOW, if the stockers rated a 6 on the scale of brakes, what would you rate the 900F rotors and calipers? I'm sorely tempted...

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by daves79x »

Nils:

First let me say that I'm glad you are getting there finally. I'd still tape the lever back (just enough to expose the bleed hole - not the whole way) and let any remaining air migrate to the m/c.

Now, I assume you have good quality pads and steel or teflon lines. If you manage to get a very firm lever, then you have the air out. Then I can tell you it takes quite a few miles to bed in the pads, usually. I'd give it 500 miles or so (I know that seems like forever), but you'll not know how good the brakes really are until then. The '80 I'm restoring now had steel lines and Ferodo pads on the otherwise stock '80 brakes and it had absolutely the best brakes of any early model I've ridden, hands down. If your brakes approach that level, you will be very pleased.

I'd rate the potential for 2-pot calipers equipped the same (premimum pads and steel/teflon lines and no air in the system) to be about 2 points higher on your scale, but if your set-up now approaches the level of the one I have here, the real world difference is small. However, on average, most 2-pot conversions are noticably better, again allowing for considerable bedding-in time.

I'd say the feel of the brakes with the 2-pot calipers is better - more linear and less 'wooden', but all-in-all I'd eventually go with the twin-piston set-up.

Dave

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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

OK, I'm sad to say this is still breaking my balls.

First-off, I realized that I had 'standard' brake lines, particularly the length between the splitter and the MC, which is way too long for use with my Interceptor bars. A two-line setup seemed like the better alternative to buying a single replacement upper line, so that's what I did. This kit uses a double banjo and runs a dedicated line to each caliper, and should be worlds easier to bleed, especially off the bike.

So tonight I went in there to install it all plus my new right-side control pod and lo and behold the troublesome right caliper is leaking again, through the piston seal.

@!#$

So I took it all off and disassembled that caliper again, and yes indeed, the sealing groove in the caliper body still felt rough. So out with the dremel wire-wheel and after a few minutes of that plus a good wash in the sink and compressed air dry, it feels smooth when i run my dental pick around it.

Inspecting the piston closely I am reminded that this is the one with the pit:

4011

The ball-point pen tip is there for scale. I have sanded this thing till it feels burr-less, but what is the collective opinion about this? This is right smack where the seal interface is. Is this the source of my grief? or was it the not-so-smooth seal groove in the caliper body?

N.

P.S. Who wants to sell me a 43 mm piston?
Nils Menten
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