Brake fluid change?

HOW does moisture get to a Brake system?????? Just removing the reservoir to check fluid level is NOT going to introduce moisture(humidity) to contaminate the system. The OEM recommendations (IMO) are CYA for them. A Motorhome would be a 10 year flush and replacement. Automobile--Never. How many people out there have had an actual first hand knowledge of a Brake Failure problem/accident that was determined to be a failure to flush their Brake fluid? In 50 years of driving and 40 years in the RV service, I have never heard of such a problem on Motorhomes or Auto's. Doug

otrfun wrote:
We siphon (with a vacuum brake bleeder) all the brake fluid out of the reservoir every year or two on all our vehicles, then refill it with new synthetic brake fluid. Takes about 12-16 oz. to refill the cars and 32 oz. for our Ram 3500. Literally takes all of 2-3 minutes to do. Can't say there's some dramatic improvement in braking, but it's nice to see the fluid clear with so little effort and cost. Still do the occasional brake bleed. When we do, the brake fluid is significantly clearer vs. how it normally looks when we don't do the siphon and fill.

This does NOT make any sense. What about the fluid in your Lines and calipers that is OLD? If you do anything it would be to flush and bleed the complete system. Not the occasional bleed. Doug

My feeling is that changing the fluid helps prevent maintenance jobs down the road, like master cylinder failures, wheel/caliper cylinder failures, and rusted hard lines. I have a 25 year old car that has had none of these failures. Without brake fluid changes I believe I would have seen them happen. If you never keep a vehicle past its 10th birthday, I suspect you're just handing off the future failures to the next owner.

dougrainer wrote:
HOW does moisture get to a Brake system?????? Just removing the reservoir to check fluid level is NOT going to introduce moisture(humidity) to contaminate the system. The OEM recommendations (IMO) are CYA for them. A Motorhome would be a 10 year flush and replacement. Automobile--Never. How many people out there have had an actual first hand knowledge of a Brake Failure problem/accident that was determined to be a failure to flush their Brake fluid? In 50 years of driving and 40 years in the RV service, I have never heard of such a problem on Motorhomes or Auto's. Doug

newer vehicle reservoir is more moisture resistant than those of the 1960's, but by no means are imune to water introduction. Water molecules are very small, smaller than oxygen, Nitrogen and most other gases. As a result water can and does penetrate many plastics and through reservoir caps.

As for failures on vehicles I've worked on, (but not maintained by me) back when rear brakes were drums, water in the fluid was often the cause of rear wheel cylinder failures which was pretty common on higher mileage vehicles that hadn't had brakes flushed. On mine, never had a rear wheel cylinder failure, but I flushed lines every year.

Doug, you mean to say you've never heard of someone riding their bakes a little too much going down a mountain and heated them up so much it cause the water in the brake fluid to boil which made the brakes useless? I've heard those stories for years. Around where I live with heavy dew the normal every morning thing, my brake fluid turns dark as it absorbs moisture pretty rapidly. I should change it yearly but I'm not that good at keeping up with it and I don't have any trips over the mountains planned - plus I come down mountains as slow as I go up them. Yes, brake fluid has an affinity for moisture and fluid reservoirs are not air tight so there's no way to prevent it from becoming contaminated unless you move to a very low humidity area in the dessert.

You are correct, brake fluid is not petroleum like most everything in the world. DOT3 and 4 fluids are made from a glycol-ether … Dot 5 from something else.
Synthetic suggest it is synthesized, but like synthetic oil, it is not. Not sure what the synthetic denotation means, but it doesnt really matter.

Fluid will absorb some water. If the brake fluid exceeds 212F then that water can turn to steam, and when you release the brake pedal and try again that steam might have pushed a lot of fluid into the resivoir, displaced by steam, and when you go to push the brakes this steam easily compresses and then there is not enough pressure to push the actual brake pads to slow down…

More likely they will get spongy and feel soft, but still stop the vehicle.
Seems like changing would be prudent, but I defer to old mechanics that laugh at this even for RVs.
Use low gear. For diesels exhaust brakes are great (for any manual shift trans exhaust brakes will work fine).

In conclusion, someone needs to keep money flowing to the mechanics

Brake fluid must be exposed to atmospheric PRESSURE for the brakes to work properly. Most brake fluid reservoirs have a tiny hole in the cap for that purpose. Except GM vehicles. Every GM vehicle I ever owned had rubber membrane separating brake fluid from atmospheric MOISTURE thus GM does not insist on regular brake fluid changes. How ever there is nothing wrong with changing it every two years.

I don't know about that. Every master cylinder I've ever encountered has had a rubber membrane between the cap and the brake fluid.

I checked my 2018 Ram manual. Brake fluid changes are not listed on the maintenance schedule. Power steering fluid is also omitted. Coolant change is recommended at 150K miles or 10 years. Oil is at 15K miles and A/T fluid and most other lubricants are at about 60K miles.

DFord wrote:
Doug, you mean to say you've never heard of someone riding their bakes a little too much going down a mountain and heated them up so much it cause the water in the brake fluid to boil which made the brakes useless?

I have definitely heard about riding the brakes really heavy doing down a grade can cause brake failure. But I have never heard that it was attributed to water turning to steam in the fluid.

Riding the brakes heavy and boiling the water in the fluid will put a gas in the fluid which will cause a spongy brake pedal. The brakes will still work, but you have to press harder or maybe pump the pedal a few times.

Kind of off topic but still relevant is that the real problem with riding the brakes too hard is brake fade. The action of braking converts momentum into heat which transfers into the rotor, caliper, bearings etc. When the brakes get too hot there is no heat transfer possible, also the pads will start to outgass between the pads and the rotors further reducing any friction. At this point you will still have a good pedal feel, but the vehicle just does not slow down. This is one of the reasons you see slotted or drilled brake rotors on race cars. The slots or holes give the gasses a way to escape from between the two surfaces. Of course like most things in life there's no such thing as a free lunch. Yes drilled and slotted rotors allow the brakes to get hotter in extreme circumstances and still work. The flip side to this is there is less surface contact with the pads so the brakes are not as strong. So on a race car they can engineer in larger brakes. On your production vehicle you're pretty much stuck with the size the manufacturer engineered.