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#4563975 - 11/04/17 02:13 PM Testing Brake Fluid with a Voltmeter
jrvn Offline


Registered: 08/11/16
Posts: 160
Loc: new jersey
I am having some spongey/soft brake issues with my Truck Toyota Tacoma, last year I purchased the truck with 49k miles and no 30k maintainence or Brake service was done to it. I did the 30k maintainence and also replaced the front Brake pads with OEM Toyota and noticed a Softer/spongey brake feel, so I decided to bleed the brakes and flush out the old fluid at the same time hoping it would stiffen the peddle up, I used some BG DOT4 fluid that I had from a previous truck which I have found out yesterday was manufactured in 2011 by BG, I contacted BG asked about sealed/unopened shelf life for this particular fluid the answer was 5 years, so scanning some YOUTUBE vids ive found one that says you can test the condition of the brake fluid with a voltmeter and I also found a few threads about it online. They said put Neg. to Grd.(battery) put Pos. into brake resovoir and the voltage reading should not be over .30 Volts the fluid no good, I got .35 Volts on my truck, has anyone ever heard or done this? I thinking the BG fluid I used last year was past due its sealed shelf life and maybe became contaminated and the net result is water compressing in my brakes giving me a soft peddle. any thoughts appreciated

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#4563984 - 11/04/17 02:18 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
jrvn Offline


Registered: 08/11/16
Posts: 160
Loc: new jersey

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#4564002 - 11/04/17 02:41 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
rollinpete Offline


Registered: 03/20/17
Posts: 453
Loc: West Ma.
I've also heard of testing antifreeze this way shrug
_________________________
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97 Ford Expl.Sport 4.0 ohv 4wd 5spddrive183k miles
Last Change;
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(Oil) Where would we be with out it.


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#4564035 - 11/04/17 03:16 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
Crispysea Offline


Registered: 04/14/17
Posts: 403
Loc: TN USA
I never thought of that, but it makes sense. The more water in the fluid, the more conductive it is. I usually just change it if it starts getting dark and/or feels spongy.

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#4564093 - 11/04/17 04:29 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
barryh Offline


Registered: 01/09/16
Posts: 312
Loc: Cheshire, England
The curious thing is not that contaminated brake fluid is conductive, but that some reaction in the brake system is generating a voltage. To measure conductivity you would normally test that with an ohm meter which has it's own internal voltage source to pass a current trough the object being measured.
_________________________
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1979 BMW R45 (Triple QX 5W40)
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#4564094 - 11/04/17 04:30 PM Re: Testing Brake Fluid with a Voltmeter [Re: Crispysea]
jrvn Offline


Registered: 08/11/16
Posts: 160
Loc: new jersey
Originally Posted By: Crispysea
I never thought of that, but it makes sense. The more water in the fluid, the more conductive it is. I usually just change it if it starts getting dark and/or feels spongy.
sometimes brake fluid will look clean and still have water in them, in my case I may have used some fluid beyond its sealed shelf life of 5 years confirmed by the manufacturer, it looks clean as heck but using the volt meter test its beyond .30 volts which means it should be flushed for new stuff, I think this has been contributing to the soft pedal issue I have been dealing with for some time. at the time I used the BG fluid I had I never thought it was over its shelf life only that it was never cracked open nor the tin seal opened/perforated.


Edited by jrvn (11/04/17 04:31 PM)

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#4564275 - 11/04/17 08:04 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
danez_yoda Offline


Registered: 07/18/09
Posts: 464
Loc: texas
Spend the $3 and flush with prestone dot3.

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#4564683 - 11/05/17 09:34 AM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
At brake job time I jack up the car, take off all 4 wheels and then open the bleeders just enough to encourage the fluid to run out but not enough to allow air into the system (slow drips) and as I'm changing the brakes it drips into the pans below each wheel. I keep topping off the master cylinder. It's easier to do this way because most of the fluid is in the lines when the brakes are worn down any way.

Then once I'm confident enough has bled out I close the bleeders and top up the master cylinder and verify no air has ended up in the system and I'm good to go until the next brake job.

Been doing this for decades and never have had a seized caliper or leaking wheel cylinders and all my brake lines last. Even the really terrible galvanized ones Chrysler was using back in the 80's / 90's that always seemed to rot.



Edited by StevieC (11/05/17 09:36 AM)
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#4565126 - 11/05/17 05:17 PM Re: Testing Brake Fluid with a Voltmeter [Re: danez_yoda]
SilverFusion2010 Offline


Registered: 06/29/11
Posts: 1658
Loc: Crawfordville FL
Originally Posted By: danez_yoda
Spend the $3 and flush with prestone dot3.


This.

And do a gravity bleed after you've pumped the old stuff out.
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#4565483 - 11/06/17 01:50 AM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
Silk Offline


Registered: 07/26/03
Posts: 4560
Loc: New Zealand
I do that method often if I have no brake fluid tester on hand. You can also do it with coolant, and anything over 600mv is no good.
_________________________
1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - Gulf Western 10W-40
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.

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#4565503 - 11/06/17 04:44 AM Re: Testing Brake Fluid with a Voltmeter [Re: SilverFusion2010]
Lubener Offline


Registered: 01/22/11
Posts: 2576
Loc: N.Ohio
Originally Posted By: SilverFusion2010
Originally Posted By: danez_yoda
Spend the $3 and flush with prestone dot3.


This.

And do a gravity bleed after you've pumped the old stuff out.

Curious, why gravity bleed when you have already bled the system of air and old fluid? Seems redundant to me.


Edited by Lubener (11/06/17 04:45 AM)
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#4565949 - 11/06/17 02:08 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
Yah-Tah-Hey Offline


Registered: 05/26/14
Posts: 3408
Loc: Columbus,Nebraska
Iffy at best. Brake fluid doesn't cost that much so just replace it every two years and enjoy a trouble free brake system for many, many miles.

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#4566022 - 11/06/17 03:38 PM Re: Testing Brake Fluid with a Voltmeter [Re: Yah-Tah-Hey]
MolaKule Offline


Registered: 06/05/02
Posts: 19042
Loc: Iowegia - USA
Originally Posted By: HosteenJorje
Iffy at best. Brake fluid doesn't cost that much so just replace it every two years and enjoy a trouble free brake system for many, many miles.


thumbsup

What voltmeter or DMM is to be used, what is the baseline resistance for aged brake fluids, etc?


Edited by MolaKule (11/06/17 03:39 PM)

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#4566238 - 11/06/17 07:50 PM Re: Testing Brake Fluid with a Voltmeter [Re: jrvn]
Silk Offline


Registered: 07/26/03
Posts: 4560
Loc: New Zealand
I work on 300mv for brake fluid. Use any DMM you like - I use a Snap-on Vantage. If you know how old your brake fluid is that great, if it's not your vehicle you have no real idea, so testing is important, and visual means nothing, just like engine oil.
_________________________
1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - Gulf Western 10W-40
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.

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#4566394 - 11/07/17 12:45 AM Re: Testing Brake Fluid with a Voltmeter [Re: barryh]
MolaKule Offline


Registered: 06/05/02
Posts: 19042
Loc: Iowegia - USA
Originally Posted By: barryh
The curious thing is not that contaminated brake fluid is conductive, but that some reaction in the brake system is generating a voltage. To measure conductivity you would normally test that with an ohm meter which has it's own internal voltage source to pass a current trough the object being measured.


thumbsup

I was wondering the same thing.

Conductivity testing measures resistance and it involves passing a current through the liquid with the voltage source provided by the ohmmeter circuit in the voltmeter.

I think the author of the link is confusing conductivity and the measurement of a voltage by a high impedance DMM.

If the DMM is measuring a voltage, then there is some kind of galvanic voltage generation
going on, and he is not measuring conductivity, but a voltage.

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