Attention: TDR Forum Junkies 
DonRam240
TDR MEMBER
In TDR issue 105, Moses Ludel in "The Long Haul" recommends a brake fluid moisture content tester that he uses to help decide when to flush and replace brake fluid. This type of tester measures fluid conductivity (or the inverse, electrical resistance), the conductivity increasing (resistance decreasing) as moisture content rises, and converts it into an estimate of the % water by volume, over a range of 0% to 4%.
The reprint in issue 105 of James Walker's issue 43 "Brake fluid expose" is a great technical resource, but doesn't discuss test methods for the fluid.
My interest is for my 2018 Ram 3500 Cummins truck in towing, and also my road racing car, for which boiling brake fluid yields alarming events on track! (Pedal goes to floor, pump pump pump, hoping the runoff area is long enough.....) Been there, don't want to return.
Researching the tester topic yesterday, I found a number of reviews or technical articles that note variations in tester results, sometimes showing wet fluid as dry, others dry fluid as wet. Technical articles indicate this is because of baseline conductivity variation between brands of fluid or batches of the same brand, making such testers not as reliable as advertised.
One other method, test strips, is for a different issue: contamination of the fluid by internal system corrosion, which raises the copper content of the fluid--which is what the test strips measure. Interesting to know, but not the cause of boiling brake fluid.
I'm hoping for one of our TDR experts to comment here about this issue, and recommend their approach to the issue, using a test method or not. Now, I replace the race car fluid annually and that's been OK so far in my 3200 lb, 440 hp Mustang. Pedal is no more than mildly softer after a half hour race, and hard again at the next start. Other vehicles, perhaps every 4 years, but can't swear to it.
My thought at the moment is this: Take a sample of the fluid I'm about to use for replacing today, and test it at baseline dry and then successively with 1%, 2%, 3%, 4% water added by volume and mixed, using a pricey electrician-quality meter to measure its resistance, which should be in the range of 220 Kohm dry, and then from 48 to 40 Kohm as it goes from 1% to 3% according to figures from a patent application for one of the test devices, found courtesy of Google: https://patents.google.com/patent/US5028144A/en
Now I have my own calibrated test results for the brand/batch of fluid actually installed, for reference when I test it periodically. As long as the distance between the test leads inserted in the fluid is held constant (resistance will be proportional to that distance), the results should be comparable to my calibration figures.
Comments solicited, please!
Don
The reprint in issue 105 of James Walker's issue 43 "Brake fluid expose" is a great technical resource, but doesn't discuss test methods for the fluid.
My interest is for my 2018 Ram 3500 Cummins truck in towing, and also my road racing car, for which boiling brake fluid yields alarming events on track! (Pedal goes to floor, pump pump pump, hoping the runoff area is long enough.....) Been there, don't want to return.
Researching the tester topic yesterday, I found a number of reviews or technical articles that note variations in tester results, sometimes showing wet fluid as dry, others dry fluid as wet. Technical articles indicate this is because of baseline conductivity variation between brands of fluid or batches of the same brand, making such testers not as reliable as advertised.
One other method, test strips, is for a different issue: contamination of the fluid by internal system corrosion, which raises the copper content of the fluid--which is what the test strips measure. Interesting to know, but not the cause of boiling brake fluid.
I'm hoping for one of our TDR experts to comment here about this issue, and recommend their approach to the issue, using a test method or not. Now, I replace the race car fluid annually and that's been OK so far in my 3200 lb, 440 hp Mustang. Pedal is no more than mildly softer after a half hour race, and hard again at the next start. Other vehicles, perhaps every 4 years, but can't swear to it.
My thought at the moment is this: Take a sample of the fluid I'm about to use for replacing today, and test it at baseline dry and then successively with 1%, 2%, 3%, 4% water added by volume and mixed, using a pricey electrician-quality meter to measure its resistance, which should be in the range of 220 Kohm dry, and then from 48 to 40 Kohm as it goes from 1% to 3% according to figures from a patent application for one of the test devices, found courtesy of Google: https://patents.google.com/patent/US5028144A/en
Now I have my own calibrated test results for the brand/batch of fluid actually installed, for reference when I test it periodically. As long as the distance between the test leads inserted in the fluid is held constant (resistance will be proportional to that distance), the results should be comparable to my calibration figures.
Comments solicited, please!
Don
