Testing Brake Fluid - Have I missed a Trick?

[jfheath]

I’ve parted company with my ST1300, about which I have learned a great deal. My new to me Spyder is 4 years old, has 8000 miles on the clock.

I took a look at the service record, and noted a comment after 2 years - “tested brake fluid” .
What ? After 2 years it should be changed, surely. So what is this testing all about? It uses DOT 4 like the ST1300.

So I looked it up. Apparently if you put the probe of a voltmeter into the fluid and the other probe onto the earth of the bike, it shows a small voltage, and from that voltage you can determine the amount of moisture.

The fluid in the reservoir is a dark tea coloured brown. It has never been changed in 4 years. It needs to be done.


But the question is - has anyone heard of this method of testing ?
Is it reliable? Is the formation of crystals in old fluid linked to moisture content or age ?
Is this just a workshop scam to charge for a service but not do any work ?

 

[Ron]

I heard something similar about coolant years ago but didn't do much more than hear it.

 

[RaYzerman]

Using a voltmeter to test coolant has always been a thing, but never heard of it for brake fluid......... After I start with a good first flush/bleed, I do a quick bleed annually..... will prevent problems in the long run.

 

[Obo]

Yes, testing brake fluid is a thing. You're testing for moisture content, as brake fluid is hygroscopic.
Set your meter to 12v DC. Put the red lead in the fluid and the black on the master cylinder metal.
If you get over 0.3v it's time to flush. It's basically turned into a small galvanic cell (multiple dissimilar metals in the braking system and moisture forms the electrolyte making it a battery) and oxidation is/can be occurring.
Read that as "a bad thing."

This doesn't replace the standard 2 year replacement and flush that the OEM recommends, but it's still a valid test if the fluids not visibly discoloured or you forget when you did it. It's also an easy test when buying a bike and the seller says, yup, it's been recently changed.
They 2 year, xxx mile change is to help prevent / minimize the moisture before this happens: aka "preventative."

Do you need to test it this way? Nope. Can you buy a ready made tester? Yup. It basically does the same as the above method, just in a purpose built tool.

Use the knowledge as you wish, or not. Don't let it stop you. That's your brake's job.

 

[jfheath]

Many thanks @Obo. I’d never heard of it. Neither have I had the tea-stain coloured fluid in the reservoir - I changed mine on the St1300 at roughly 12-18 months - usually when I had the wheels off while the new tyres were being fitted. Given the issues that many others have reported with the SMC this seems a sensible course of action.

While I was looking for a new-to-me bike from photos, I used the sight glass window in the master cylinder reservoir as a ‘litmus test’ colour scale for how well the bike had been serviced. I’m rather dismayed that with my very low mileage Spyder, although the dealer told me on the phone that it was ‘in the service area’ just after we had done the deal, I assumed that it would be having a full service. When I eventually got it, the fluid was really quite dark and from the records, had never been changed since new. The Spyder does not have a handlebar brake lever - which takes a bit of getting used to - the reservoir is under the body work.

New learning curve….

 

[ST1100Y]

Yes, testing brake fluid is a thing. You're testing for moisture content, as brake fluid is hygroscopic.
Set your meter to 12v DC. Put the red lead in the fluid and the black on the master cylinder metal.
If you get over 0.3v it's time to flush. It's basically turned into a small galvanic cell (multiple dissimilar metals in the braking system and moisture forms the electrolyte making it a battery) and oxidation is/can be occurring.

Got me one of those digital testers, same principle by checking conductivity of the brake fluid (decreasing with % of humidity)...

 

[Sadlsor]

Yeah, but who among us really wants to buy another tool...?

 

[RaYzerman]

You don't need any tools if you follow my recommendation. When you do a full flush on a new-to-you bike, know the system is clean, then do a quick bleed annually, takes very little fluid. You're well under the 2 year recommended interval, even with any residual in there, well under any moisture concerns, and those SMC's and M/C's and calipers stay clean. You have no worries about having maximum braking at all times. Costs you next to nothing for prevention. And you can buy the small bottles of DOT4. An ounce of prevention is worth a pound of cure.

 

[Al st1100]

Older Rolls Royces held about a gallon of brake fluid, a tester there would be useful on a motorcycle...no.

 

[ST1100Y]

You don't need any tools if you follow my recommendation. When you do a full flush on a new-to-you bike, know the system is clean, then do a quick bleed annually, takes very little fluid. You're well under the 2 year recommended interval, even with any residual in there, well under any moisture concerns, and those SMC's and M/C's and calipers stay clean. You have no worries about having maximum braking at all times. Costs you next to nothing for prevention. And you can buy the small bottles of DOT4. An ounce of prevention is worth a pound of cure.

Yeah, but at times I've to deal with other motorcycles then those under my regime...

 

[SMSW]

After a full brake job on my car (pads & rotors, as needed)I asked my trusted car mechanic why he did not flush the brake system with new brake fluid. He replied that his customers don't want to pay for it, and since none of the other service stations around do a flush with a complete brake job, he cannot either and remain competitive. I took my car home and did it myself.

Auto service is approaching what we have found with Honda dealers and old ST's. I took my GMC van in for illuminated ABS lights on the dash and the first thing the do is roll it forward, slap sensors on the front wheels and tell me I need an alignment. No bouncing, settling of the suspension, just roll 'er up and check. I told them to fix the warning light issue (was under warranty) and my friendly mechanic later checked the alignment on his rack and said all was w/in spec.

 

[Al Gully]

I’ve parted company with my ST1300, about which I have learned a great deal. My new to me Spyder is 4 years old, has 8000 miles on the clock.

The fluid in the reservoir is a dark tea coloured brown. It has never been changed in 4 years. It needs to be done.

I guess I should check my wife's F3 CanAm Spyder brake fluid. It's a 2016 with 8000 miles on it.
We bought it new in 2017.