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Testing Brake Fluid with a Voltmeter #4563975
11/04/17 02:13 PM
11/04/17 02:13 PM
Joined: Aug 2016
Posts: 195
new jersey
jrvn Offline OP
jrvn  Offline OP
Joined: Aug 2016
Posts: 195
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

Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4563984
11/04/17 02:18 PM
11/04/17 02:18 PM
Joined: Aug 2016
Posts: 195
new jersey
jrvn Offline OP
jrvn  Offline OP
Joined: Aug 2016
Posts: 195
new jersey

Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4564002
11/04/17 02:41 PM
11/04/17 02:41 PM
Joined: Mar 2017
Posts: 570
West Ma.
rollinpete Offline
rollinpete  Offline
Joined: Mar 2017
Posts: 570
West Ma.
I've also heard of testing antifreeze this way shrug


Pete.
97 Ford Expl.Sport 4.0 ohv 4wd 5spddrive184k miles
Last Change;
Penn. Plat. HM. 5w30
Fram xg8a, Fram CA8141

I like my oil (slippery).

Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4564035
11/04/17 03:16 PM
11/04/17 03:16 PM
Joined: Apr 2017
Posts: 435
TN USA
Crispysea Offline
Crispysea  Offline
Joined: Apr 2017
Posts: 435
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.

Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4564093
11/04/17 04:29 PM
11/04/17 04:29 PM
Joined: Jan 2016
Posts: 315
Cheshire, England
barryh Offline
barryh  Offline
Joined: Jan 2016
Posts: 315
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.


Barry

1979 BMW R45 (Triple QX 5W40)
2009 Mercedes C180K (Shell Helix Ultra 5W40)
Re: Testing Brake Fluid with a Voltmeter [Re: Crispysea] #4564094
11/04/17 04:30 PM
11/04/17 04:30 PM
Joined: Aug 2016
Posts: 195
new jersey
jrvn Offline OP
jrvn  Offline OP
Joined: Aug 2016
Posts: 195
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.

Last edited by jrvn; 11/04/17 04:31 PM.
Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4564275
11/04/17 08:04 PM
11/04/17 08:04 PM
Joined: Jul 2009
Posts: 601
texas
danez_yoda Offline
danez_yoda  Offline
Joined: Jul 2009
Posts: 601
texas
Spend the $3 and flush with prestone dot3.

Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4564683
11/05/17 10:34 AM
11/05/17 10:34 AM
Joined: Aug 2008
Posts: 18,619
Ontario, Canada
StevieC Offline
StevieC  Offline
Joined: Aug 2008
Posts: 18,619
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.


Last edited by StevieC; 11/05/17 10:36 AM.

'18 Highlander - AMSOIL SS 0w20 / ATF / Severe Gear
'06 Santa Fe - 535,000km AMSOIL SS 0w30 / ATF (R.I.P)
Re: Testing Brake Fluid with a Voltmeter [Re: danez_yoda] #4565126
11/05/17 06:17 PM
11/05/17 06:17 PM
Joined: Jun 2011
Posts: 1,755
Crawfordville FL
SilverFusion2010 Offline
SilverFusion2010  Offline
Joined: Jun 2011
Posts: 1,755
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.


2010 Ford Fusion SE 3.0L V6, 178k miles M1 HM 10w-30
Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4565483
11/06/17 02:50 AM
11/06/17 02:50 AM
Joined: Jul 2003
Posts: 4,754
New Zealand
Silk Offline
Silk  Offline
Joined: Jul 2003
Posts: 4,754
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.
Re: Testing Brake Fluid with a Voltmeter [Re: SilverFusion2010] #4565503
11/06/17 05:44 AM
11/06/17 05:44 AM
Joined: Jan 2011
Posts: 2,719
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,719
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.

Last edited by Lubener; 11/06/17 05:45 AM.

The "thinking" man's friend.
Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4565949
11/06/17 03:08 PM
11/06/17 03:08 PM
Joined: May 2014
Posts: 3,667
Columbus,Nebraska
Yah-Tah-Hey Offline
Yah-Tah-Hey  Offline
Joined: May 2014
Posts: 3,667
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.

Re: Testing Brake Fluid with a Voltmeter [Re: Yah-Tah-Hey] #4566022
11/06/17 04:38 PM
11/06/17 04:38 PM
Joined: Jun 2002
Posts: 19,236
Iowegia - USA
MolaKule Offline
MolaKule  Offline
Joined: Jun 2002
Posts: 19,236
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?

Last edited by MolaKule; 11/06/17 04:39 PM.

Reading is fundamental; understanding is not a given ability.
Re: Testing Brake Fluid with a Voltmeter [Re: jrvn] #4566238
11/06/17 08:50 PM
11/06/17 08:50 PM
Joined: Jul 2003
Posts: 4,754
New Zealand
Silk Offline
Silk  Offline
Joined: Jul 2003
Posts: 4,754
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.
Re: Testing Brake Fluid with a Voltmeter [Re: barryh] #4566394
11/07/17 01:45 AM
11/07/17 01:45 AM
Joined: Jun 2002
Posts: 19,236
Iowegia - USA
MolaKule Offline
MolaKule  Offline
Joined: Jun 2002
Posts: 19,236
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.


Reading is fundamental; understanding is not a given ability.
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