Brake Fluid Maintenance - Important!

[Land-Pilot]

I'm posting this in response to another post I read regarding brake fluid.

Folks, please be aware that when you service your brakes you should also be checking the state of the fluid. Brake fluid should be changed completely periodically as it is hygroscopic (meaning it attracts moisture), which can cause internal corrosion issues and also cause the fluid to boil at high temps from braking thus leading to brake fade & failure. So since some of your rigs are of considerable size and weight and the brakes are under high loads during down hill driving I would recommend replacing it at least once a year to keep the system in good shape. Also if you cannot see through the fluid to the bottom of your master cylinder reservoir then it certainly needs a full replacement, which means having it sucked all the way through the lines until fresh clear fluid is seen at each wheel slave cylinder bleed screw. The recommended approach is to bleed the system starting at the furthest wheel from the master cylinder reservoir and making your way to the front.

 

[WanderingBiker]

good info..... thats the most overlooked part of the system

 

[user 2252]

One method that works for me is to get a what they call a one man brake bleeder. If you really want to attempt this, ask your local parts guy for this.

Then your local dollar store will have a turkey baster I'm sure, get that and while your at the parts guy get a couple of small cans of brake fluid.

Simply stir the brake fluid in the master cylinder with the turkey baster gently squeezing the bulb a couple of times, you want everything in that fluid to be suspended. Now, suck out that gunk with the turkey baster being careful not to suck it dry, we don't want to introduce air to the system. Fill the master cylinder with fresh brake fluid and repeat until you have a master cylinder full of clean brake fluid and if you use your finger during this process to wipe the inside of the master cylinder you will have cleaned it too!

Ok now with the one man bleeder attached to the passenger rear wheel bleeder screw, pump the brake pedal slowly, sucking that clean brake fluid from that clean master cylinder through the brake lines until you get clean brake fluid coming out that bleeder screw. Bam! Now go to the driver side rear wheel and........thats right, bleed  untill you get clean brake fluid. Don't let the master cylinder go dry, check it and keep it full of brake fluid. Empty your bleeder into a jug to help with disposing of the waste later. Please be mindful of the delcate ecosystem that makes the desert what it is. Finish up wth the front and Bam clean, fresh brake fluid througout your braking system. It's more fun if you bring along a friend to help you.

 

[Weight]

This good advice for the older wreaks we drive. And a good practice when replacing brake parts. Quality, modern brake fluid is not hygroscopic. Use the good stuff.

 

[Weight]

Harbor Freight hand vacuum pump for flushing brakes works well enough.

 

[highdesertranger]

DOT 3, 4, and 5.1 are hydroscopic meaning they readily absorb water. DOT 5 is not hydroscopic but DOT 5 is not compatible with 3, 4, 5.1.
do not mix DOT 5 with the others. wiki on brake fluid,

https://en.wikipedia.org/wiki/Brake_fluid

highdesertranger

 

[Land-Pilot]

This good advice for the older wreaks we drive. And a good practice when replacing brake parts. Quality, modern brake fluid is not hygroscopic. Use the good stuff.

As per Wikipedia:
DOT 2 (mineral oil) & DOT 5 (silicone) fluids are not hygroscopic and don't have to be replaced when the water content becomes too high. Ideally, silicone fluid should be used only to fill non-ABS systems that have not been previously filled with glycol based fluid. Any system that has used glycol-based fluid (DOT 3/4/5.1) will contain moisture; glycol fluid disperses the moisture throughout the system and contains corrosion inhibitors. Silicone fluid does not allow moisture to enter the system, but does not disperse any that is already there either. A system filled from dry with silicone fluid does not require the fluid to be changed at intervals, only when the system has been disturbed for a component repair or renewal.

As per ME
If your vehicle is new enough to be using silicone type fluids from the factory then sure you do not have to be as concerned as per the statement above. However, if your vehicle is older and you decide to replace your older type fluid with newer silicone based fluids then be aware because it will need to be completely drained and dried out as it will not disperse any moisture still trapped in the system, and getting all the moisture out of the system requires some work and possibly replacing parts. Silicone based fluid is also more compressible than glycol based fluid, leading to brakes with a spongy feeling. It can potentially suffer phase separation/water pooling and freezing/boiling in the system over time - the main reason single phase hygroscopic fluids are used.

Still today most vehicles, even newer one, use non silicone fluids. Exceptions might be military vehicles and aircraft but these are also maintained far more vigorously and more often than ours and using stringent procedures.

Anyone in doubt then I recommend reviewing the Wikipedia web site for more information and consulting with your vehicle manufacturer.

 

[johnny b]

This good advice for the older wreaks we drive. And a good practice when replacing brake parts. Quality, modern brake fluid is not hygroscopic. Use the good stuff.

OK, this is just wrong. The 'good stuff' I guess you're referring to would be the latest DOT 5.1 glycol based fluid. It is compatible with DOT 3 and DOT 4 and can be used. However it IS Hygroscopic (with a G), and absorbs moisture.

[HDR - I'll just assume you suffered a typo...I know you're a good mechanic.] 

One of the most confusing things is that the newer fluid was labeled "5.1" even though it is glycol based and IS NOT COMPATIBLE with DOT 5 silicone.
Silicone fluid has its uses, but normal everyday use on the road is not one of them. I use it in my race kart but even that is not as common as it once was since most of the new European karts use DOT 4. Another use of silicone fluid is show cars and museum cars that sit for long periods. Mainly due to not ruining paint if spilled and its stability over time without water absorption.
The Military uses silicone but is currently looking for a replacement as they adapt to ABS in newer vehicles. (they did a study/test in 2017 on ABS pumps and found silicone fluid affected the seals and also lacked the 'lubricity' of glycol based fluid causing piston wear)

If your vehicle has ABS (anti-lock brakes)...DO NOT USE DOT 5 SILICONE, EVER.

I'm not aware of any road vehicles that came with DOT 5 silicone fluid...and that is the only silicone brake fluid...I'm also not aware of "newer silicone based fluids" nor of "silicone type fluids".

 

[closeanuf]

Vonbrown as usual you make sense once again.  In the old days I used a pop bottle with a hose from the bleeder into fresh brake fluid in the pop bottle.  I haven't tried that with antilock brake systems though.  Changing brake fluid once a year sounds a little overboard to me, but what do I know?  I'm 70 and I've only been messing with cars since I was 15.

 

[highdesertranger]

oops you are right johnny b. it is a typo my bad. thanks for catching that. highdesertranger

 

[Minivanmotoman]

FWIW, There is no fixed standard for a brake fluid change. One year seems too frequent for most imho unless driving lots of miles, doing it yourself and you enjoy the work for top maintenance. A vehicle owners manual could give you a guideline or recommended change interval.

Many factors such as mileage driven, driving habits, environmental conditions. Not getting much moisture in the arid Southwest. General rule of thumb that I have heard is two years or when the fluid is Amber to dark colored. Definitely needs changing then as it should be clear. Many good tips from others on diy methods and YouTube of course is full of tips as well.

The same goes for all of the other fluids, change them on a regular basis too, transmission, power steering, anti freeze coolant, oil.

 

[Zil]

It is a good practice to overhaul wheel bearings, brakes, shoes, pads, cylinders, calipers, rotors, and drums. Rubber lines and even rusty steel lines. How about the master cylinder and vacuum boost. Then flush the system as well as you can. I used one gallon of brake fluid. Use at least DOT 4 even 5point1. They are not as troubled by water as DOT 3. I would not put a 10 year old vehicle on the road without overhauling the brakes as listed above. Don't forget the parking brake.