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Depressing caliper pistons #4757520
05/15/18 03:40 AM
05/15/18 03:40 AM
Joined: Nov 2007
Posts: 3,996
United States of America
mjoekingz28 Offline OP
mjoekingz28  Offline OP
Joined: Nov 2007
Posts: 3,996
United States of America
I was wondering if it is good practice to open the brake bleed screw before compressing the piston while installing new pads.

It seems it would expel the fluid you cannot remove with a flush (as I have read on here) and also make the piston retract easier as it doesn't have to push fluid into the reservoir.

Downside though is a slight bleed is required.

Re: Depressing caliper pistons [Re: mjoekingz28] #4757548
05/15/18 05:46 AM
05/15/18 05:46 AM
Joined: Oct 2012
Posts: 4,779
Taiwan
Ducked Online content
Ducked  Online Content
Joined: Oct 2012
Posts: 4,779
Taiwan
Why is that a downside?

Admittedly a full bleed would be better, but a slight bleed seems better than none.

Re: Depressing caliper pistons [Re: mjoekingz28] #4757549
05/15/18 05:47 AM
05/15/18 05:47 AM
Joined: May 2005
Posts: 10,388
ROCHESTER, NY
Char Baby Offline
Char Baby  Offline
Joined: May 2005
Posts: 10,388
ROCHESTER, NY
IMO, this is the best way to depress the pistons as it doesn't push back dirty fluid into the system. Many techs don't do this and may not have any issues either way. But, I like opening the bleeder.

However, first try pushing back the piston(just a little) without opening the bleeder. If the piston doesn't move or is difficult to push back, you may have a slightly blocked hydraulic line/brake hose. If the piston is easy to push bake w/o the open bleeder, then proceed to open the bleeder and finish pushing back the piston. This is only for testing and something I like to do.

Continue to bleed the whole system as good PM.

Last edited by Char Baby; 05/15/18 05:48 AM.

"Retired"
-----------------------------------

'80 Firebird FORMULA V8/4bbl-purchased "NEW"
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Re: Depressing caliper pistons [Re: mjoekingz28] #4757583
05/15/18 06:58 AM
05/15/18 06:58 AM
Joined: Oct 2010
Posts: 7,033
Michigan
A_Harman Offline
A_Harman  Offline
Joined: Oct 2010
Posts: 7,033
Michigan
I always bleed the caliper until clean fluid comes out prior to pushing the pistons back in. It just keeps junk from getting up the brake pipes.


1985 Z51 Corvette track car
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel
1972 GMC 1500 shortbed project truck
Re: Depressing caliper pistons [Re: mjoekingz28] #4757613
05/15/18 07:53 AM
05/15/18 07:53 AM
Joined: Jan 2012
Posts: 415
hawthorne, Ca.
46Harry Offline
46Harry  Offline
Joined: Jan 2012
Posts: 415
hawthorne, Ca.
I always open the bleeder screw when depressing the caliper piston as it keeps the trash that has built up from being pushed back into the hydraulic system.

Re: Depressing caliper pistons [Re: mjoekingz28] #4757649
05/15/18 08:34 AM
05/15/18 08:34 AM
Joined: Mar 2008
Posts: 5,995
Michigan
ZZman Online content
ZZman  Online Content
Joined: Mar 2008
Posts: 5,995
Michigan
I assume opening the bleeder makes it super easy to push the piston in?


2003 Mercury Grand Marquis. PP HM 5w-30 and Fram Ultra
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Re: Depressing caliper pistons [Re: mjoekingz28] #4757658
05/15/18 08:43 AM
05/15/18 08:43 AM
Joined: May 2009
Posts: 12,250
N.H, U.S.A.
ARCOgraphite Offline
ARCOgraphite  Offline
Joined: May 2009
Posts: 12,250
N.H, U.S.A.
Just use a big flat blade screwdriver and wedge it between the rotor and floating side of the caliper and lever compress. This is for the NOT RECOMMENDED quick pad slap. No fancy Clamps required.

Now, It Better and more Professional to do a complete flush all 4 corners.

If I was working on a nice car I liked; I would bleed when compressing through a rubber hose into a waste can of DOT 3. I HATE brake fluid - always have. The suff down at the business end is watery, corrosive and just plain bad.

Last edited by ARCOgraphite; 05/15/18 08:47 AM.

2014 Nissan Rogue S CVT, OC#9 41392mi-QSUD10W30 + M110A CHAMP Filter; 2017 Subaru Crosstrek CVT OC#2 ?? mi-SOA/Idemitsu 0w20 + SOA Filter
Re: Depressing caliper pistons [Re: mjoekingz28] #4757684
05/15/18 09:01 AM
05/15/18 09:01 AM
Joined: Jan 2017
Posts: 1,547
VW Fanboy Island
maxdustington Offline
maxdustington  Offline
Joined: Jan 2017
Posts: 1,547
VW Fanboy Island
If you are going to bleed anyway, what difference does it make if some dirty fluid gets pushed up the brake line? Like a foot or two?


03 Jetta AWP/09A 205k kms
Edge 0W40 + Mann 719/30
Re: Depressing caliper pistons [Re: mjoekingz28] #4757737
05/15/18 09:30 AM
05/15/18 09:30 AM
Joined: Dec 2006
Posts: 7,770
Toronto, Canada
KrisZ Offline
KrisZ  Offline
Joined: Dec 2006
Posts: 7,770
Toronto, Canada
I don't do this.
My rationale is that, if the junk is in the piston, contacting the seals, etc. and not having negative effects, what harm will it do if it gets pushed back into the steel brake lines? It's not going to go all the way back to the master cylinder.

Also, I have never seen the "junk" people mention. Maybe few "floaters" when looking directly at a strong source of light. Otherwise the brake fluid in my vehicles looks like aged whiskey.


2015 Dodge Grand Caravan-27k miles.
2006 Mazda 3-163k miles
Re: Depressing caliper pistons [Re: mjoekingz28] #4757744
05/15/18 09:38 AM
05/15/18 09:38 AM
Joined: Dec 2016
Posts: 195
Wisconsin
emmett442 Offline
emmett442  Offline
Joined: Dec 2016
Posts: 195
Wisconsin
I still think this is all a myth.

Where is the "dirt" and "junk" in the fluid coming from? The fluid in filling the caliper bore is the same fluid that's in the lines and master cyl. It's a sealed system. If air and fluid can't get passed the caliper piston, how's dirt and junk going to? There's no reason for the fluid in the caliper to be any more dirty than the rest of the system.

I prefer to compress with the bleeder closed so I can "feel" the condition of the calipers and the rest of the system. It's harder to notice a sticking caliper piston, collapsing brake hose, etc if the bleeder is open.

I do crack the bleeder loose afterwards, but that's to enure that the bleeder itself stays free and doesn't sieze in the caliper. Every time I check or replace the brakes, I remove the bleeder, anti sneeze, and reinstall.


2011 Ford Crown Victoria LX 4.6L V8 auto
2009 Chevrolet Malibu LT 2.4L I4 auto
1974 Dodge D200 360 V8 4 speed manual
Re: Depressing caliper pistons [Re: emmett442] #4757783
05/15/18 10:23 AM
05/15/18 10:23 AM
Joined: Aug 2003
Posts: 10,870
Buffalo, NY
JTK Offline
JTK  Offline
Joined: Aug 2003
Posts: 10,870
Buffalo, NY
I've never seen a used caliper bore without junk in it. I dunno if it's from the piston moving in/out, seal material, or the fact it's the closest area to the outside world.

Problem is, the heavy bits are going to lay and stay in the bottom no matter what you do. The bleed screw is up top. If you're confident the bleeder is going to move and re-seat, I'm all for cracking it prior to compressing the piston.

I'm hit/miss in doing this. Depends how much time I've got and how in-depth I wanna go.

Last edited by JTK; 05/15/18 10:23 AM.

2017 Ram 1500 4x4, 3.6L. 2016 Nissan Quest SV (Babe magnet IV)
Re: Depressing caliper pistons [Re: mjoekingz28] #4757918
05/15/18 01:07 PM
05/15/18 01:07 PM
Joined: Sep 2004
Posts: 7,604
Marshfield , MA
andyd Offline
andyd  Offline
Joined: Sep 2004
Posts: 7,604
Marshfield , MA
I've the hole so packed with crud, I had to use a needle to clear it. BF attracts water, water and air cause corrosion in the cylinder bores when the water boils off.


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2
Re: Depressing caliper pistons [Re: mjoekingz28] #4758355
05/16/18 12:39 AM
05/16/18 12:39 AM
Joined: Jun 2015
Posts: 527
New York
NoNameJoe Offline
NoNameJoe  Offline
Joined: Jun 2015
Posts: 527
New York
I too have no idea where the crud comes from but I've seen it. Sometimes after doing a brake fluid change at all four wheels I'll find the jar has some kind of sediment on the bottom. The jar is capped except for a hole at the top for the tube to go through so it must have come from the fluid.

There's also some kind of sediment inside the reservoir sometimes.

As for whether I open the bleeder when I depress the piston, I like to change the fluid at the same time I do anything that involves depressing the piston. I usually change the fluid first, then depress the piston without opening the bleeder since I know I have clean fluid. I have depressed the piston with the bleeder open sometimes too though.


2015 Civic LX Coupe
Re: Depressing caliper pistons [Re: ARCOgraphite] #4758418
05/16/18 05:54 AM
05/16/18 05:54 AM
Joined: Oct 2012
Posts: 4,779
Taiwan
Ducked Online content
Ducked  Online Content
Joined: Oct 2012
Posts: 4,779
Taiwan
Originally Posted By: ARCOgraphite
J I HATE brake fluid - always have. The suff down at the business end is watery, corrosive and just plain bad.


Then someone isn't changing it often enough. Maybe me.

Re: Depressing caliper pistons [Re: emmett442] #4758428
05/16/18 06:13 AM
05/16/18 06:13 AM
Joined: Oct 2012
Posts: 4,779
Taiwan
Ducked Online content
Ducked  Online Content
Joined: Oct 2012
Posts: 4,779
Taiwan
Originally Posted By: emmett442


I still think this is all a myth

Where is the "dirt" and "junk" in the fluid coming from?........It's a sealed system.......................................................... Every time I check or replace the brakes, I remove the bleeder, anti sneeze, and reinstall.


Maybe someone is putting anti-seize in it? Y'know, oil-based, rubber incompatible stuff?

That (fairly slim admittedly) possibility aside, if it was a completely sealed system, you'd never have to change your brake fluid.

You do.

So it isn't.

Given that it isn't, its a fair bet that it isn't uniformly permeable, so there may be local concentrations of water. I've seen it stated that water gets in via hose permeability. If that's true, it perhaps also gets in through the piston seal. This would tend to produce a higher concentration of water in and behind the pistons.

In addition, there is movement and friction in the pistons (and master cylinder) which will tend to put debris from seal and bore wear into the fluid.

I've never seen an analysis of the distribution of water and debris in the system, but anecdotally the first bit of bleed tends to be darker, which tends to confirm expectation.

So if its a myth, its at least an unusually reasonable one, as myths go.

Last edited by Ducked; 05/16/18 06:21 AM.
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