Author Topic: Brake fluid behind the caliper pistons  (Read 4402 times)

Online balvenie

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Brake fluid behind the caliper pistons
« on: March 23, 2015, 10:06:48 PM »
            This is supposed to be where the most contaminated fluid is, in calipers with chrome plated steel pistons, according to Guzziology. Does this apply to an '04 Cali? I am supposed to "open the nipple and bleed the system enough to fill the purge hose a few inches, then press each caliper piston.......back into the caliper as far as it will go. Close off the nipple......."
            Is the piston pressing necessary?
Oz
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oldbike54

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Re: Brake fluid behind the caliper pistons
« Reply #1 on: March 23, 2015, 10:14:02 PM »
 Yes, no, maybe  :D Sorry Bill  :-[ Yes , would really be my best advice .

  Dusty

Online balvenie

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Re: Brake fluid behind the caliper pistons
« Reply #2 on: March 24, 2015, 03:59:26 AM »
               I knew it 8) ;D
               I suspect that two pairs of hands will be necessary and was hoping to get away with omitting this step because my assistant is not available til Saturday week. In the meantime I might just do a standard fluid replacement so I can have a ride.
Oz
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Offline acogoff

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Re: Brake fluid behind the caliper pistons
« Reply #3 on: March 24, 2015, 04:02:46 AM »
     The best way I have found is to use a mightyvac with brake bleeder attachment and suck out a couple ounces of fluid at the caliper to get rid of any contamination. Of course all while making sure the reservoir doesn't go low on you. Not sure if moving the piston about is required. I have a ford pickup that likes to build up moisture in the rear calipers and stick on if I don't flush a bit out once in a while.
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Re: Brake fluid behind the caliper pistons
« Reply #3 on: March 24, 2015, 04:02:46 AM »

Online Perazzimx14

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Re: Brake fluid behind the caliper pistons
« Reply #4 on: March 24, 2015, 05:12:49 AM »
I assume you are changing the brake fluid? If so moving the pistons is not needed. Buy a $30 mity-vac at your local auto parts store and vacuum bleed the brakes. When bleeding/changing brake fluid in motorcycles I typically run two or 3 master cylinders full of fresh fluid through.

Another way I have been using lately (worked great on linked brakes) was reverse bleeding. You can see video's on youtube if you are interested.
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dilligaf

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Re: Brake fluid behind the caliper pistons
« Reply #5 on: March 24, 2015, 07:07:27 AM »
I've used Mity-Vac off and on since 1983 or so.  Makes changing the break fluid by one person easy. This is what I do when the Mity-Vac breaks.  Attach a piece of clear vinyl tubing, just like what comes with the Mity-Vac, that is long enough to reach from the bleed nipple to the handlebars.  If I'm changing fluid I remove all the old fluid from the reservoir and refill with fresh.  Open the nipple. When fluid appears in the tubing start pumping.  Have a container ready to catch the old fluid. Don't allow the reservoir to run out of fluid.  ::(  Nothing to it and you don't get all pissed off when your Mity-Vac fails.  ;D  :BEER:
Matt     

Offline Mike Tashjian

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Re: Brake fluid behind the caliper pistons
« Reply #6 on: March 24, 2015, 07:24:57 AM »
Fluid behind the Pistons tends to stay there as you bleed the caliper.  Using a couple of wooden wedges to force the Pistons in will make it easier to get the most out of a fluid change. If your reservoir is near full be sure to remove some of the fluid before pushing the Pistons in.  This is a good time to check how hard the Pistons are to move in their bore. They should move smoothly.  After bleeding be sure to clean any fluid with plenty of soapy water.  Mike

Offline drlapo

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Re: Brake fluid behind the caliper pistons
« Reply #7 on: March 24, 2015, 07:30:45 AM »
 a large C clamp works well to push the pistons
of course Harbor Freight has a cheap tool to do the job

Offline John A

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Re: Brake fluid behind the caliper pistons
« Reply #8 on: March 24, 2015, 07:37:03 AM »
When you push the pistons in, do it evenly or they get stuck in the bore. No big deal just pump it out again but if you find they don't go in check that you are not pushing unevenly.
John
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redrider

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Re: Brake fluid behind the caliper pistons
« Reply #9 on: March 24, 2015, 08:42:01 AM »
I use the bleeder from HF. It connects to the compressor and has a fluid bottle on the m/c. Works great and you can see the old coffee colored stuff change to a clear tan. With a bit of practice you can flush a whole bottle of fluid without stopping and I'm confident the swirling of the incoming fluid will displace any of the nasty. Especially good with the clutch as well.
Be careful when or if you push the pistons back. They may go too far and block the orifice although I've only seen this with Asian calipers when replacing pads.

Offline Tobit

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Re: Brake fluid behind the caliper pistons
« Reply #10 on: March 24, 2015, 08:49:20 AM »
If you've let the pads wear very thin the pistons will be far out of the bores.  Before pressing them back in, check their rubber boots for cuts, clean off any dirt or crud and proceed slowly.  Best to open the bleeder and let it flow out through a hose rather than loosen the reservoir cap and push it back there.  Don't want to overflow and spill.

Tobit

Edit:  If the piston dust boots are torn, there is likely rust or other undesirable swarf on the pistons.  Rebuild the caliper.
« Last Edit: March 24, 2015, 01:06:31 PM by Tobit »
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Online Stevex

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Re: Brake fluid behind the caliper pistons
« Reply #11 on: March 24, 2015, 02:41:03 PM »
Just replaced the brake fluid in my Honda CB1300 last night; my front caliper pistons sit below the bleed nipple and are last in line from the brake pipe and nipple. There's no way I can see that doing a regular bleed would replace the fluid behind the pistons, so I removed the calipers, cracked the bleed nipple (with bleed tube and a couple of inches of fluid in it) and bottomed the pistons out. Now I know I've got as much new fluid in there as I can get.
« Last Edit: March 24, 2015, 02:42:06 PM by Stevex »
Steve
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Online Perazzimx14

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Re: Brake fluid behind the caliper pistons
« Reply #12 on: March 24, 2015, 02:49:02 PM »
If you push the pistons into the caliper make sure you pump up your brakes after your finish bleeding them. Its a bad feeling rolling down the driveway and you go to hit the brakes for the 1st time realizinf they aren't there. Then the frantic pumping of the foot pedal and hand lever start to happen as panic sets in.
It's the ones who've cracked that the light shines through!

Online rodekyll

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Re: Brake fluid behind the caliper pistons
« Reply #13 on: March 24, 2015, 03:30:44 PM »
My solo bleed method is to get a jar with a lid.  Punch a hole in the lid big enough to pass a plastic hose.  Put an inch or so of brake fluid in the jar.

Get a plastic hose that fits the bleeder nipple tightly.  It needs to be long enough to reach the jar when the jar is securely set BELOW the level of the bleeder.  By secure I mean it won't tip over when you disturb the hose, which will happen when you open and close the bleeder.  Attach one end to the bleeder and the other through the hole in the lid and into the brake fluid.

Open the bleeder and slowly pump.  You will see bubbles.  The first bubbles are the air leaving the hose.  Any more will be air leaving the brake system.  Pump until the bubbles stop.  You will also see the old fluid come out and mix with the new.  If you are purging your system, watch for fresh fluid to begin pumping out.


I push the pistons back by hand with the pads still in place, with a screwdriver or other pry bar -- with the bleeder open.  This (mostly) empties the caliper.  Then I close the bleeder and pump it up/bleed normally.

I keep suggesting that folks get a bleeder banjo bolt (has the bleeder in the top) and replace your front m/c hose bolt with it.  Then you've got a bleeder on the high point of the line and life is easier.  Bleeding becomes an easy one-person operation.  I just wrap a cloth around the bleeder (and box-end wrench), pump it up, open the bleeder, let the handle bottom out, close the bleeder and repeat till the handle feels good.  It's easy enough that I can burp the line in the morning during my pre-flight check.

Rear line bleeding can be made easier with a bleeder bolt too.  I'll let you imagine how it would set up for your bike's rear brake setup on account of I can't see it from here.

All $0.02, but tested and approved.

Offline lucky phil

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Re: Brake fluid behind the caliper pistons
« Reply #14 on: March 24, 2015, 03:48:26 PM »
If you push the pistons into the caliper make sure you pump up your brakes after your finish bleeding them. Its a bad feeling rolling down the driveway and you go to hit the brakes for the 1st time realizinf they aren't there. Then the frantic pumping of the foot pedal and hand lever start to happen as panic sets in.
Heres a tip if this happens to you.......stop working on brakes. The whole idea of bleeding the brake system is to remove air and get a firm leaver or pedal with minimum travel.
How you could competently bleed the brake system and end up in the situation you describe astounds me.
Ciao
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Online Stevex

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Re: Brake fluid behind the caliper pistons
« Reply #15 on: March 24, 2015, 04:50:09 PM »
Heres a tip if this happens to you.......stop working on brakes. The whole idea of bleeding the brake system is to remove air and get a firm leaver or pedal with minimum travel.
How you could competently bleed the brake system and end up in the situation you describe astounds me.
Ciao

Yep, part of any maintenance on bike, car, in fact any machinery, should always include a functional test afterwards.
« Last Edit: March 24, 2015, 04:50:46 PM by Stevex »
Steve
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2005 Aprilia Tuono
Chief mechanic to wife's 696 Monster

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Online balvenie

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Re: Brake fluid behind the caliper pistons
« Reply #16 on: March 24, 2015, 06:27:01 PM »
            You blokes have an overwhelming wealth of experience :bow  which will take me a Very long time to absorb ;D

             Thankyou very much ;-T
Oz
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Harper's Moto Guzzi : Go Ride , Break Parts, Call me!
Harper's Moto Guzzi. Where we still answer the phone, use the highest quality parts, and also do Transmission, rear drive, and carb rebuilds fast. Call us at 816.697.3411 and get your problems resolved.
http://www.harpermoto.com
Advertise Here