DIY Brake Fluid change?

[Volfy]

BTW, I forgot to mention another problem with not flushing/bleeding your brake fluid periodically. AIR is another contaminant that can - and does - get into the brake fluid. Yes, the whole system is supposed to be closed-loop, and there are seals everywhere to keep the fluids in and contaminants out, but... the seals are not perfect and their effectiveness wear out over time. Also, the reservoir is vented to atmosphere to some degree. It isn't basically open air like brake systems were long time ago, but it still needs to accommodate for volumetric expansion/contraction due to temp fluctuations.

On more than one occasion, I have bled all calipers perfectly clear of air bubbles, quite often overdoing it just to be absolutely sure. Then the next time I go bleed the same car again (maybe a couple 3 yrs later), I noticed air bubbles coming out of the nipple. Not much, but enough to know for sure I was not seeing things that weren't there. Air was definitely getting into the system one way or another. Now, air doesn't travel downward, so the air went in pretty much at the calipers. This happened with a variety of cars, so it isn't some defective system in a particular brand/model. Although, certain vehicles are more susceptible than others. Some Italian bikes have rear brakes are notorious for allowing air intrusion. I had an '08 Aprilia RSV1000R that was like that. The rear brake master cylinder sits right next to the exhaust pipe and, regardless of how carefully I bled it, the rear brake would go spongy and loose effectiveness in a short time. I can bleed it out again, and the same thing would happen in short order. That was, until I bought rearsets that cam with master cylinder relocation mounting points built-in. That helped a lot. Though, no system is 100% immune from it.

 

[ElChanclo]

BTW, I forgot to mention another problem with not flushing/bleeding your brake fluid periodically.

Is there a way of completely replacing OEM brake fluid with Racing brake fluid at home?

As I understand it, you can't just bleed the system dry because that would introduce air, but you also can't drain the old fluid below the MIN level of the reservoir, so you'll have about 1/5th OLD fluid when you fill up with NEW fluid. So when you bleed the lines you're introducing a mixture of 20% old and 80% new. Which is fine if you're worried about moisture or just broken down fluid, but not good if you're concerned about wet boiling point.

 

[Volfy]

Is there a way of completely replacing OEM brake fluid with Racing brake fluid at home?

As I understand it, you can't just bleed the system dry because that would introduce air, but you also can't drain the old fluid below the MIN level of the reservoir, so you'll have about 1/5th OLD fluid when you fill up with NEW fluid. So when you bleed the lines you're introducing a mixture of 20% old and 80% new. Which is fine if you're worried about moisture or just broken down fluid, but not good if you're concerned about wet boiling point.

Racing brake fluids like Motul RBF600 and 660 are DOT4, so they are 100% compatible with any other DOT4. Even if you flushed all 4 corners clear of old fluid, today's brake systems with ABS will leave some old fluid trapped behind the ABS pump and valves. It's not much and the next time you actuate the ABS, the trapped old fluid will mix with the new and be diluted out anyway. For some vehicles, especially motorcycles, there are aftermarket OBD2 service utilities that offer an ABS bleed mode that will open the valve(s) to let you bleed out the trapped fluid. Both my BMW and Triumph have such utilities. I've not come across ones for car/truck, but they probably also exist. Dealer service have them, I'm sure.

Realistically though, it isn't such a big deal. wet boiling point matters most right at the caliper, because that is where your brakes will get extremely hot. Up near the ABS pump, the temp will at most stabilize to the same underhood temp, which typically does not get anywhere close to WBP temp of DOT4.

Just flushing the old fluid out of the calipers and the main lines, you'll get 99% of the benefit of having dry fluid.

To me, it's far more important to watch the reservoir and not let its level drop any where close to the min mark, as you bleed the lines. Let it drop too low, and the suction force can draw air down into the reservoir drain (same effect as the "swirling cyclone" of a draining bathtub). So keep it topped off frequently with new fluid.

 

[ElChanclo]

Just flushing the old fluid out of the calipers and the main lines, you'll get 99% of the benefit of having dry fluid.

That's good news, I was way overthinking it. I ordered some bottles of the Motul 600, almost the same as the 660 and WAY cheaper than the Castrol SRF. I know it's not the most noticeable "upgrade" but sounds like a good idea for the track.

 

[Kazz]

Is there a way of completely replacing OEM brake fluid with Racing brake fluid at home?

You will find demonstrations all over the internet on this. I believe you start with the corner furthest from the master cylinder. Top off the master cylinder with fresh fluid and slowly start bleeding at each corner (slowly working the brake pedal) while not letting the master cylinder's reservoir get too low like Volfy said. Just keep topping it off to the line. Keep it up with each corner and fill the master cylinder when you're finished.

They make tools to help suck the fluid through, etc. But it can be done manually.

Again, find someone's confirmed process on Youtube or somewhere first to verify the stops. Very straightforward. A friend helps.

 

[ElChanclo]

You will find demonstrations all over the internet on this.

I've rebuilt brake calipers and had to bleed the brake lines before, I have a neat little suction gun that makes it a synch (I hear pressurizing the system is better though, less likely to pull in air bubbles at the nipple).

My concern was clearing out all the OEM fluid from the system so it's all replaced with NEW fluid, meanwhile keeping air out of the whole thing.

Sounds like draining the reservoir to MIN then topping up with racing fluid and bleeding the lines gets you 90% of the way there.

 

[StingertimeNC]

yes, at least 90% of the way, which is plenty for Track duty. Fluid and pads are all that you need.

 

[JSolo]

Owner's manual calls for a dot 4lv fluid. This is not the same as dot 4. Pricier too.

 

[Volfy]

You'd be fine. A lot depends on the track. If it's a very technical track and no long straights, brake use will be less. That's what I prefer anyway, so I tend to shy away from the faster tracks.

Regardless of whether you manage to replace 90% of the old fluid, or 95%, or even 100%. The brand new dry fluid will start sucking moisture from the air and start sliding down toward Wet boiling point from day 1. Realistically, 10 months of RBF660 might not be a whole lot better than brand new spec DOT4.

To me, brake fluid is just another consumable. No different than brake pads, tires, and engine/diff oils. Good to stay on top of everything, but no need to fuss over any particular one too much.

 

[Volfy]

Owner's manual calls for a dot 4lv fluid. This is not the same as dot 4. Pricier too.

I've never bothered with the low viscosity stuff. Then again, I don't live up in the north, where that might possibly be more of an issue. Down here, I'm much more worried about the heat and the humidity, neither of which does brake fluids any favors.

However, if you're interested, here's a good reference page with some good data and info:

Brake Fluid Explained - Everything You Need To Choose Which Is Best For You

The topic of brake fluid is often overlooked when it comes to street-driven cars; it's not sexy, doesn't make your car any faster, it just quietly goes about its business. This article covers some of the questions we're asked the most such as which brake fluid is best for your car, how often to...

blog.fcpeuro.com

Note that RBF600 actually has a higher WBP than RBF660, so even though RBF660 is better when brand new uncontaminated, RBF600 would perform a bit better when both have been in service a while and absorbed moisture. This is why typically, high performance racing fluids need to be changed out sooner. Like a lot of other things, there is no free lunch. Everything is a compromise. What I use right now is closer to ATE 200 on that list. If I ever upgrade, I'd likely go with RBF600.

 

[LordKOTL]

I've never bothered with the low viscosity stuff. Then again, I don't live up in the north, where that might possibly be more of an issue. Down here, I'm much more worried about the heat and the humidity, neither of which does brake fluids any favors.

However, if you're interested, here's a good reference page with some good data and info:

Brake Fluid Explained - Everything You Need To Choose Which Is Best For You

The topic of brake fluid is often overlooked when it comes to street-driven cars; it's not sexy, doesn't make your car any faster, it just quietly goes about its business. This article covers some of the questions we're asked the most such as which brake fluid is best for your car, how often to...

blog.fcpeuro.com

Note that RBF660 actually has a lower WBP than RBF600. What I use right now is closer to ATE 200 on that list. If I ever upgrade, I'd likely go with RBF600.

Love the knowledge you're bringing.

If it wasn't such a pain in the arse to do, I'd really consider swapping to DOT 5. Then water isn't an issue.

 

[Hawk853]

Love the knowledge you're bringing.

If it wasn't such a pain in the arse to do, I'd really consider swapping to DOT 5. Then water isn't an issue.

Water becomes more of an issue with DOT 5 since if it collects in the system and creates little water colonies that corrode from the inside and can boil more easily.

The hydroscopic effect is intentional for lower maintenance brake systems. That’s also why DOT3/4 isn’t good forever. Eventually it becomes saturated with water and the droplets start to demulsify. The boiling point of water soaked brake fluid is still much higher than water alone.

I had motorcycles with DOT 5 systems and never had issues, but flushing them is 10 times easier and all the plumbing was stainless and calipers aluminum.

 

[Volfy]

The hydroscopic effect is intentional for lower maintenance brake systems. That’s also why DOT3/4 isn’t good forever. Eventually it becomes saturated with water and the droplets start to demulsify. The boiling point of water soaked brake fluid is still much higher than water alone.

I wouldn't say the hydroscopic effect is intentional. Alcohols like Glycol ether and borate ether are used in DOT3/4 primarily because of their high boiling point. The secondary benefits are excellent lubricity and fairly constant viscosity (relative to temp), compared to mineral oils. The fact that they are hydroscopic isn't exactly sought after, but a property that needs to be managed.

Just like alcohol used in gasoline mix, it can be both a plus and a minus. For applications that spend a lot of time in storage, like boats and generators, the prolonged hydroscopic effect tend to saturate the ability of the entrained alcohol to hold the absorbed water, so they tend to phase separate and cause problems. Then again, I remember back before the federally mandated additional of ethanol, it was common practice to add alcohol to gasoline, especially in the frigid northern winters, precisely because of its ability to dissolve in both gasoline and water. One common brand was HEET, which was advertised as a "water remover", and it was basically just isopropyl alcohol.

As for DOT5... it isn't widely adopted for several reasons. One is they are tend to aerate in ABS pumps, which is a big no-no. Another is they are a bit more compressible than the alcohols, so in larger vehicles with longer brake lines, the brake feel can be rather spongy.

 

[ElChanclo]

I know some of those words!

 

[Ah GetFd]

Never had a problem with a 22yo that did 245,000kms, a 21yo that did 170,000, kms and a 14 yo that did 130,000kms but then you yanks drive cars to their death, A 250,00kms car here is an end of life old car. So we are talking 150,000 miles then we throw them away.

 

[Ohiocruiser]

Never had a problem with a 22yo that did 245,000kms, a 21yo that did 170,000, kms and a 14 yo that did 130,000kms but then you yanks drive cars to their death, A 250,00kms car here is an end of life old car. So we are talking 150,000 miles then we throw them away.

Than, where shoud I put one of my previous car with over 260k miles, that woud have around 360k miles if I didn't sell it, mainly because I expected run away inflation, and bought a stinger. You will be very surprised to learn how many people are keeping their cars way past 150k miles. Some, because they can't afford new one, some ,because they just like it. And you gotta keep it consistent. If you throwing the car at 150k miles, why not advocate for 25-30k miles oil changes. I am sure it will be enough for 150 life span.

 

[Volfy]

You know... wet boiling point of DOT4 is 311F. Even DOT3 is 284F. There are a lot of cars that are lightly driven in on the road and won't ever see their calipers - and for sure anywhere else in the brake system - get that hot. Heck, even for me, in every day commute most of the time I am a bonafide hypermiler. I avoid touching to brakes and coast as much as I can to maximize mpg. Usually, my brakes don't even get hot enough I couldn't put my hand on it.

For reference, for home hot water heater, the recommended set temp is 120F. That should give you an idea why most automotive brakes would work just fine with wet DOT3/4... in most traffic situations. I don't doubt a great many drivers never bother to flush their brake fluid because of this.

Does that mean you don't ever need to? Well... that's your judgement call. I know I do occasionally take family on vacations to places like Colorado and have to drive through mountain passes. On long descent, we avoid riding the brakes, of course, and use engine braking as much as possible, but... brake use in those situations are still unavoidable and they still will get much hotter than driving in city stop-and-go. I've seen cars at the bottom of Pikes Peak with smoke coming out of their wheels!

And I do also enjoy me some canyons and twisties carving when the opportunities present themselves. Heaven forbid some of us would have the galls to do AutoX or, OMG... even Track Days. Yeah... good luck with wet old DOT3/4.