Checking your brake fluid

[SteveD]

yeah, I know, change it annually and she'll be right (Haven't heard from She'llbe for a while ) Thought it's a handy thing to know though.

[barryh]

yeah, I know, change it annually and she'll be right (Haven't heard from She'llbe for a while ) Thought it's a handy thing to know though.

Just checked my car which is overdue a fluid change after 3 years and it measured 80 mV so that's well inside the 300 mV limit. I wonder if there is a sliding scale from 0 to 300 mV that gives an indication of the fluids condition.

[Rob Frankham]

I've heard of this test but I have to say that it is something I'm not totally convinced about. A better description of the test is from a website called CDX automotive states:

DVOM–galvanic reaction test: The majority of today’s braking systems use a combination of dissimilar metals. Manufacturers use aluminum in pistons and housings, and steel in brake lines and some wheel cylinders. When moisture mixes with brake fluid, a galvanic reaction (corrosion) can occur. The higher the moisture content in brake fluid, the higher the galvanic reaction and the greater the erosion/corrosion it causes. The DVOM–galvanic reaction test uses a DVOM to measure the voltage created by the galvanic reaction due to the level of moisture in the fluid

It sounds plausible... however... if the 'galvanic reaction' is dependant on different metals used in the braking system and the amount of water in the fluid... which is totally acceptable... then surely the value of the reaction will be dependant not just on the amount of water in the fluid but on the type of metals used in the brake system, the proportion of different metals and indeed their relative locations. If the system were to entirely use plastic components, I wouldn't expect any galvanic reaction at all. One that used components all of the same metal would not show much galvanic reaction. Or to look at it another way, a system that uses an aluminium master cylinder and caliper, lined pipes and mild steel pistons might be expected to give very different results to one that uses copper brake pipes and a cast iron caliper... even changing the pistons from mild steel to stainless might be expected to make a difference.

In essence, I'd expect any system that produces a reaction of 0.3 volts to be so badly contaminated as to be potentially dangerous but the point where the reaction is 'acceptable' is impossible to specify for any individual system. As you say, a much better approach is to make sure the system is flushed regularly...

Rob