How often do you flush you brake fluid?

done as part of the annual service.

for the price, zero point to not do it given its a hydroscopic fluid.

 

Surprised by need in brakes made after the 1980’s. Upgraded fluids, etc. I guess moisture from sitting? I see in race cars racing, but not in street cars sitting??

I mean, millions of cars on road never had fluid changed - never. Then you have the .001 who swear it destroys the car if not done.

I am just asking. Or musing. I know people do it a lot for an annual service. A lot of nice cars with new fluid in them


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Abso-friggen-lutely -- and the day before any track event.

How many of those other cars can reach 180 MPH, and then attempt to stop in minimal distance ?

 

Confirming what others have said.

Recommended: You change brake fluid in all vehicles 1x per year due to water absorption or if you boil your fluid on track, whichever comes first.
Push it: Change the fluid every 2 years
Risk it: > 2yrs means you can't complain when your pedal goes squishy in an emergency braking event

You can buy yourself time switching to Castrol SRF which has nearly the same boiling point wet/dry. This is also what I use on my GT4 racecar.

 

Every 2 years in the 355s and 993s. Sometimes I push to 3 yrs in my other cars. I think the climate is a factor as well. If I lived in an area with higher humidity, I change it more often.

 

race fluid in 2 cars like every other track day
Street fluid in other car once a year
I believe the race fluids pull more moisture from the air then a dot4

404 diesel chevy, once a year also that thing for some reason the fluid turns black in a year from moisture and it dont rain here

 

For my F355 Challenge, just before each track event. This is specified in pre-event tech inspection checklists of the groups I track with.

 

If you don't change your fluid and it absorbs water, you won't have a problem with sudden braking in an emergency situation. What you would have a problem with is pedal fade when the brakes get very hot, e.g. on the track or aggressive driving on a downhill mountain road where there's lots of braking. Water boils at a lower temp than brake fluid. When the fluid absorbs water and your braking heats the calipers past 212F, the water in the fluid turns to steam. Brakes are a hydraulic system; water doesn't compress, but steam does. Turn your fluid into steam and you get a mushy pedal. But no, you're not going to crash because a deer ran into the road and you have to slam on the brakes.

I would bet that 80 percent of the cars you drive past every day haven't had their brake fluid flushed in many, many years and they brake fine.

 

Very true. However it is worth noting that the moisture can/will rust the brake lines from within. I think this is more of an issue in cars that don't get driven often, like a Ferrari.

 

Pedal is not going squishy from a single hard stop, even if the fluid is 3+ years old.

Now, driving a mountain pass or something, maybe. The reason to change it every 2 years (or more frequently) is to avoid internal corrosion and to keep the bleeder screws from corroding and "welding" themselves to the calipers.

 

Including or excluding a panic stop from 180 MPH ?

 

Including

 

This isn't hard. Water boils at 212F/100C. Does the handful of seconds it takes to stop from 180mph create sufficient heat to boil the moisture in the calipers? Of course not. I'm sure the pad/rotor friction area gets very hot stopping from 180mph. But that's not enough to cause pedal fade. The heat has to soak all the way into the caliper to the fluid. That doesn't happen in 5-10 seconds. It happens, in the fastest scenario, starting after several minutes of intense braking, such as on a track with a lot of turns and no straights.

 

1) your are all forgetting about the corrosive properties of water in your braking system.

2) you can split hairs all day long over the boiling point. its interesting academically, but the point is do you want to chance it? personally no. ( ive done it on carious bikes through hard driving on the toad) its like buying a cheap motorcycle helmet; you are automatically shortlisted for a darwin award!!

 

I have been testing with a fluid tester for many years as a routine and my experience is vastly different than yours.
Environment, type of fluid and type of use does however play a part. DOT tests show an average of 3% absorption per year nationwide based on testing their own fleet which is why they use that as a standard. In Central Texas I get from 1 - 4% percent per year testing same cars, same fluid on subsequent annual service visits on various client cars depending on individual use. In Coastal California it was slighty less of a spread.

 

Based on DOT testing we know 2 things for sure. Brake fluid will get water in it in a closed or sort of sealed system cars have. We also know water degrades the fluid. This may not matter to some but what will eventually matter is it will rust the interior of the system. Again if you flip cars every few years this may not matter but it will matter to well advised future owners. A Toyota or Ford caliper can be replaced cheaply and annual changes may not make economic sense. A 20 or 30 year old Ferrari caliper is a very different story. I can tell you from direct experience that on any of the newer cars with 6 piston calipers and CCM brakes you will care very much about brake fluid after the 1st brake caliper overhaul. Paul Hill is doing very well selling selling replacement stainless pistons for them. Many of those need new pistons before they need new pads.

 

Pulling water from the air is not the issue. It is known from DOT testing silicone brake fluid gets water in it at nearly the same rate. The difference is since silicone does not take the water in solution it stays separate. Water is heavier that silicone fluid so the water settles to the bottom in concentrate. What else is at the bottom? The calipers. Where does the heat come from? The calipers. So very near the calipers we have water which has a boiling point of 212 instead of possibly diluted brake fluid which has a boiling point at last 100 degrees higher. Also silicone was not authorized by TUV because it is compressible and gets more compressible as it gets hotter. In their opinion dangerously so.

 

Another major problem with silicone fluid is it is almost impossible to get all the air out when bleeding. That is why you get a soft pedal. I met a fellow many years ago at a Porsche meet that drove his car across country to the California location and he mentioned he had silicone and he lost his brakes coming down the mountain into Salt Lake City but regained them at lower altitude. He tried bleeding again but still couldn't get all the air out. I told him on his way back to bleed again as soon as he reached high altitude. He wrote me later he couldn't believe how much air he was able to get out due to the pressure making the air bubbles larger and easier to flush out. As for the damage to calipers, a large cottage industry developed back in the '70s to re-sleave with stainless for '65-82 Vette cast iron calipers which were notorious for corroding due to lack of brake bleeding. Doesn't take a lot of moisture to do bad things to calipers and pistons located inside.

 

Yeah when they came out with silicon thats when it hit the fam. crystalized lines in the Harleys locking up the brakes
Mixing fluids
Would be nice to have a "absolute" for these guys to see. Parts store guy, brake fluid over there, Amazon review . Yuuup best brake fluid I ever used for my engine

 

As someone who just did a full rebuild on all 4 corvette calipers on a '78 that sat for 20 years, the sleeves work great for keeping the seals from tearing...the rest still goes to crap.

sjd

 

The real question is how many reach 180MPH