Brake Fluid Flush

[SierraHotel]

Beyond which DOT number brake fluid you use, how often do you flush the brake system and renew it? I’ve looked to see if any of the TM’s have fluid replacement schedules for the brake fluid (DOT 3 or DOT 5) and have yet to find any. Nor is it discussed (that I can find with my admittedly lacking skills) on the pinnacle of ancient military vehicle information, SteelSoldiers.

With DOT 3, I would assume (scary, right?) that the fluid should be flushed every…um, let’s call it several…years because the moisture content of the DOT 3 should be getting a tad oppressive at that point.

However, with DOT 5, it appears (to me at least) that everyone seems to think that it’s a one-time thing and does not need to be flushed at any point. I’ve read many a post (on more than just SteelSoldiers) of people touting 10, 20 and more years of DOT 5 with nary a problem and it looked as good today as it did when they put it in.

From my own perspective, I just gutted my brake system. The master cylinder and air pack were filled with…um…chunky mud. I sincerely doubt that it had been changed since it went through overhaul in 1992. Unfortunately, I must hang my head low as I hadn’t done anything since getting it 10 years ago. Ignorance is certainly bliss…stupid, but blissful. I believe the muck was 25 year old DOT 3 (no, it wasn’t DOT 5), rust and junk from having to fill it through the hellhole in the floor (I’m sure Einstein designed that one), with all the slipstream fluids, dust, dirt, mud, disassembled body parts of insects and GEICO squirrels, et. al. Oh yeah, a remote master cylinder is definitely in part of my reassembly. Basically put, 10 years is too long for DOT 3 (and probably DOT 5), 25 years is _________ (fill in the blank with the word of your choice). I have yet to decide what type of fluid to fill my virginal brake system with…but if the changing schedules are the same, it will be DOT 3 (for my wallet’s sake if nothing else).

So…how often do you change your brake fluid…be it DOT 3 or DOT 5, or if you are getting fancy, DOT 4 or DOT 5.1?

 

[gimpyrobb]

Dot 3 is cheap. If you go that route flush it every couple years and you will be good to go.

 

[clinto]

Regardless of fluid, I'd flush it every 4 or 5 years. If you go underwater, more frequently.

BFS won't absorb moisture but that doesn't mean it won't get in the system. The moisture will end up in the low spots (I think) versus just being throughout the system. One way or another you need to flush the system regularly.

The other thing to consider is that moisture isn't the only thing that can contaminate the system. As the system ages, the rubber and neoprene seals start to break down and they clog the system. I assume you can get some metal shavings as well. Regular flushings will clear the system of these contaminants.

Also, I have DOT5 BFS competitively priced, new 2017 manufacture. PM me.

 

[rustystud]

Dot 5 doesn't need replacing, but it needs a little "cleaning" every few years to remove any moisture or "crud" that has gotten into the system. What I mean with a little cleaning is to either have someone pump-up the brakes or have the power bleeder connected and go to each bleeder and allow a little fluid to come out. 30cc is fine. If you do this on a regular basis you will never have a build-up of moisture in your system. Dot 3 must be totally replaced and have the system flushed out every 5 years max. Most vehicle manufactures recommend every 2 to 3 years. Also with DOT 5 you don't have as much "rubber" failure as you would with DOT 3 as the silicone actually helps lubricate and protect the rubber parts. Unlike DOT 3 which has alcohol and "attacks" rubber parts.

 

[SierraHotel]

Thank you to all three of you for your considered responses. While I am by no means an expert in brake fluids, I have done way too much research on the subject of DOT3 (and its affiliates) and DOT 5. Basically put, you can find whatever answer you want if you read enough. Everyone tends to agree that DOT3 et al, needs to be completely replaced within 2 to 4 years, partially because of moisture absorption, but I believe mostly because of corrosion inhibitor exhaustion. That’s kind of a scary proposition because I never considered fully flushing the brake fluid in any of my vehicles (nor really heard of it) prior to my research into which fluid to use. I tend to agree with Gimpy and Clint that regular flushing is the best way to go (regardless of fluid type)…and being that DOT 3 is more economical, that is the route I will likely be taking.
DOT 5 on the other hand, does not have much information regarding the full flushing of the system. Most of it centers on people who own collector vehicles that do not get regular mileage using it (that is the one thing that has me wavering toward DOT5). I only found one DOT 5 manufacturer that recommended flushing in their printed literature. However, communication with others recommended the flushing interval be between 3 and 5 years. Generally, this interval was recommended because of moisture presence, more than anything else. However, I do absolutely agree with Clint that there are a number of other things that should be flushed out, other than water.
The fact that DOT 5 will absolutely not mix with water does disturb me. Having as much as 5% water mixed in solution with DOT 3 does not disturb me near as much as a pocket, or pockets, or 100% water against a metallic object (brake line, wheel cylinder, etc.). I know that 100% water will cause corrosion, 5% in solution…maybe not. However, I’ve not read any posts or articles that I would consider credible in large enough numbers to consider this a major issue with DOT 5. Additionally, generally most consider water to be heavier than silicone (I’m not a chemist, so I don’t know for certain), and if this is the case, I would not think bleeding would pull all of the water(not moisture) from the wheel cylinders, because it would be below the bleeder valve. Again, I’ve not read any voluminous reports of corroded wheel cylinders with DOT 5.
I do know that moisture will enter the brake system, regardless if you have DOT 3 or DOT 5. It will contaminate the fluid faster with DOT 3 because of its hydrophilic properties. However, the EPDM used in many of the hoses and seals (from the master cylinder, to the air pack, to the wheel cylinders to the hose connections) will allow moisture (not water) to pass through them, which will eventually condense and accumulate once the temperature reaches dew point. EPDM, I do know, as well as the transfer of moisture laden air. Oil, grease and diesel fuel will cause EPDM to swell, sometimes alarmingly.
I don’t think that DOT 3 will eat the EPDM seals significantly faster than DOT 5, as the fluid and seals need to be engineered to be compatible with one another. I believe either one will perform fine so long as they are the only fluid that are ever used in the system. Switching from one version to the other…well, I believe that is where the issues will arise…especially if you flush the system with alcohol as I’ve seen suggested many times. I believe that the DOT 3 causes more of a swell with the seals than the silicone, which can be a good thing…depending on your feeling of the matter.
The original reason for the question was to see if anyone was flushing their DOT 5 brake fluid. Personally, I’d recommend it (and probably buy from Clinto at his ‘competitive prices’). The things I’ve learned in my research, combined with my previous lack of knowledge of DOT 3 scare me (I’ve got 3vehicles to flush in the very near future), but I’m not entirely sure that DOT5 adequately removes the need for full flushing. In the end, it is your vehicle and your choice (and I didn’t want to start another DOT 3 vs DOT 5 war). I just hope that I’ve written this rambling narrative well enough that someone can decipher it, and it helps someone in the correct direction for them (whatever that may be).

 

[rustystud]

There is plenty of information out there concerning DOT 5 if you look. It is not the "be all, end all" of brake fluids by any means, but it is the best in an older "non" anti-lock brake vehicle. DOT 5 will foam if cycled quickly like in a anti-lock brake system. Also most brake seals are not made from "EPDM" material. They are usually Nitrile. EPDM is a recent material (relatively speaking) and was not used until around the 1980's . If you look up any older vehicles brake information from the manufacturer you will see that most recommend that all rubber parts are changed out at around every 5yrs max. In the vehicle repair industry they used that information to get the customers to agree to a complete brake job. I know as I was part of that when I worked at the dealerships.
Now about flushing DOT 5 completely, I disagree. The cost of DOT 5 is pretty high for one. Second DOT 5 does not break down like DOT3 will. It will last easily for decades as it is a "complete compound" . You chemist types will know what that means better then I do. So your only needing to "clean" out the crud that forms at the end of the brake line. Also your comment about not getting out all the water is incorrect. The pressure in the brake lines is more then enough to completely clean out the wheel cylinder. Fluid comes in at one point and exits out the other, usually totally opposite from the other so the fluid is swirling out the wheel cylinder. Unless the wheel cylinder is so full of crud that no amount of fluid will clean it you don't need to tear it down every 5 years when using DOT 5. I'll give you a personal experience. In my CUCV I totally replaced all the brake lines with stainless steel. I then reinstalled new DOT 5 fluid and have been running it with no problems for 25 years now. Last year I rebuilt my front calipers and had no wear or rust in them. In fact they could have lasted another 25 years with no problems. I just wanted to make sure they where OK for our trip. What I do is every year I bleed a small amount of fluid out at each bleeder. That way there is no crud or water left in the system.
Now DOT 3 with it's "alcohol" base will actually attack the seals, causing them to "dry out" . I've seen this so many times in the past. The seals will actually "break" and crumble in your hands. You will never see that with a DOT 5 system.
There is a very valid reason the military went with DOT 5 brake fluid, and contrary to popular belief it is not all about vehicles sitting for long periods of time. DOT 5 is just superior to DOT 3 in almost everyway, except price.
So my recommendation is to study some more. The information is out there. Stay away from "Forums" where you most likely will find misleading information and peoples "opinions" . That includes what I've written here (not that I'm trying to mislead you) . Just get the facts for yourself.