Technical Getting Rid of Dot 5 Brakes Fluid

Here's the situation. 48 Lincoln had power brake setup with dual master cylinder under floor and remote fill, worked great, but had dot 5 synthetic fluid in the lines. Not being smart enough to leave well enough alone, I put a Speedway disk brake kit using Ford PU rotors and Impala calipers, adjustable proportioning valve with brake light switch, and 2 lb residual valve in front lines.

Problem: Now can't get bubbles out of system. Tried too much pressure and ended up with fluid on floor, tried pumping brakes, and finally vacuum sucking. System is now well flushed with about 2 quarts of Dot 3 and still endless bubbles and pedal that goes to floor. Is Dot 5 really that bad, or am I missing something? What to do?
Thanks
Abe

 

Think you need to flush and purge your system with denatured alcohol, or something similar, prior to introducing an entire new brake fluid into the lines.

 

Dot5 is the best there is and has nothing to do with your problem

 

You're sucking air into the system somewhere if you have bubbles. I changed a system from Dot5 to Dot3 and did as was suggested above- flushed the system with a lot of denatured alcohol- then ran the dot three - bled the system and fixed the soft pedal situation I was experiencing with Dot5
Have you tried reverse bleeding the system?
As in - pushing brake fluid from the bleeder screw back through the system to the MC with a syringe and small hose.

 

I had that fluid in my car but didn't like the feel so I flushed entire system out with methylated spirits to dissolve all the fluid and any remnants. I then replaced all the rubbers seals in master cylinder and calipers (x4), blowing out the hard lines with compressed air to ensure they was clean. I then replaced fluid and bled system, job done. Sounds like your system requires a pressure bleed on each wheel to remove residual / trapped air. My MC has built in residual valve. Start at furthermost wheel and work towards closest wheel.

 

if I may ask?
why would dot 5 give a soft pedal ?

 

I also never had a problem with soft pedal or air with Dot 5 in a few vehicles. It is a little more of an effort to bleed, not sure why, possibly the efect of air in the solution, does not purge as easy as with Dot 3.....

 

The endless air when bleeding is probably coming from the bleeder screw. The threads are not tight fitting so when you loosen the bleeder screw, it will suck air at that point. What I do, is take the bleeder screw out, wrap it in Teflon tape, screw it half way or more in, make sure your bleeder hose is going up hill from the bleeder screw. You also have to make sure that your bleeder hose connection is snug also. When that wheel is good, then move to the next wheel and do the same thing. A soft pedal is air in system, with dot 5, don't pump the brake pedal a lot, just once, bleed until there are no big bubbles, then you are on the right road. If you have a connection leaking in the line somewhere and its a small leak, then its impossible to get a hard pedal. Small leaks are only found with pressure so you have to bleed the system real good and then have someone keep pressure on pedal and you go looking for a drop of brake fluid somewhere, the smallest leak will keep you from removing air. Good luck

 

I've seen guys put the calipers on the wrong side, upside down, bleeder at the bottom. Yo can never get the air out. I too have used DOT 5 with great results, it don't hurt paint, don't suck moisture, best for cars that might set of an extended period of time. Make sure your calipers are on the correct sides.

 

Dot 5 is all we run and it acts just like Dot 3 in all respects. We primarily use it because it doesn't suck up our Florida humidity and it doesn't ruin paint if spilled on it. I redid my 27 after about 15 years and the original Dot 5 came out looking brand new.

Buy yourself some of those self bleeders, they make it so much easier to bleed the system.

Don

 

Sounds like the problem is not with the DOT 5 but a leak in the system. I would trace every line and look for leaks or drips to figure out where the air bubbles are coming from.

 

Problem is not DOT 5 ! DOT 5 will feel soft until heated up from use . Sounds to as if seal washers on the hoses or calibers reversed from side to side

 

Once you get air in DOT 5 it's very hard to get out. The bubbles stay in suspension in the fluid and don't seem to collect. Pump the pedal very slowly and usually only once each time you crack a bleeder. I agree that you have a leak somewhere. Been using DOT-5 in my 50 for some 10 plus years with original master cylinder and disc brake conversion on the front. Very satisfied with it.

 

I don't think that the fluid was the whole problem-my caliper/bracket arrangement did not put the bleeder screw at the very top-so it was difficult to bleed. As someone Flathead 4D mentioned above, I think I had a lot of air suspended in the fluid as a result of continuously bleeding the system in an attempt to gain a firmer pedal. I changed out to Dot 3 and was able to reverse bleed the system and get the air out and improve the pedal feel .

 

I've put DOT 5 in everything I've built, restored. Trailor queen I finished in '95, dot 5 in there, brake system still perfect. Rods, sandrails, its in there. Only thing I don't like about dot 5 is the price. but its a lot cheaper than ruined paint thx to dot 3 or 4. It does seem to have a thinner viscosity to me and newly plumbed brake systems seem to reveal the potential leaks quicker.

 

Thanks for the comments, even though this is not my thread.

 

Truth.

 

DOT 5 would give a soft pedal because it is more likely than DOT 3 to contain air bubbles within the fluid. Properly installed (pour slowly) and bled (slowly) it shouldn't be a problem. I am running it in my '32 Ford with a '46-'48 brake system.

Charlie Stephens

 

I read somewhere that DOT 3 absorbs water microscopically and DOT 5 absorbs same amount but the moisture is suspended in "pockets" in the system separated from the fluid

 

Not true. If it were, DOT 5 would be even worse than DOT 3 for water related problems.

Difficulty in getting all the air out is a real problem. You can pick up a quart of DOT 5 fluid and shake it a couple times, and it'll take 3 or 4 days for the air to come back out of suspension. Slow bleeding with a pressure bleeder works best. You can have a brake system that's working fine, and you're sure all the air is out. Take that car to an elevation that's 3000 to 4000 feet higher than where it commonly lives, and if there's any air in the system your brakes will go away. Like no pedal whatsoever. The bubbles expand due to reduced atmospheric pressure at higher altitudes. Been there and done that on an OT 69 Vette with DOT 5, and its scary as hell.

 

DOT 5 ( silicon ) brake fluid has a lot of pluses , but the main reasons it has never been used by OEMs is paint system contamination ( will not attack dry paint, but cause fish eyes if it is anywhere near where you are painting ), and it is very hard to get all of the air out of it. Some systems are worse than others- but keep on bleeding......

 

You are missing something. Worked fine in previous configuration. Changed a bunch of parts. Doesnt work now. What changed, the parts or the fluid, hmmm......?

 

I've been running DOT 5 in vehicles for years. Never had any issues, what hasn't been stated is the higher boiling point of DOT 5 over DOT 3 so under severe braking DOT 5 will not boil and fade as quick as DOT 3 may. Joe

 

Let me rephrase my answer. Any water that gets into the system, and it will over time, will not be absorbed by Dot 5 but will form pockets of water.

 

So how do you figure this water gets into the system over time? Water gets into DOT 3 because glycol based brake fluid is hygroscopic. That means it actively seeks and absorbs water from any available source. DOT 5 is not hygroscopic, so it doesn't attract water.

What's likely worse than water absorption is the fact that DOT 3 also absorbs road salt.

Contrary to popular belief that all moisture enters thru the m/c reservoir, most moisture is actually absorbed thru the brake hoses.

General Electric did a bunch of tests back in the early 70's, looking at water and salt absorption of DOT 3 versus DOT 5 brake fluids. Why GE? Because they're the original developer and patent holder of most silicone based compounds on the market today, including silicone brake fluid.

They found new-in-the-can DOT 3 contained 15 times as much water as new DOT 5. DOT 3 starts absorbing moisture from the air as soon as its container is opened.

They tested both fluids in identical new brake hoses, filled with fluid and capped. The hoses were submerged in water and in water with 5% salt, to simulate driving in wet conditions and driving in wet conditions with road salt present.

After a week, the DOT 3 fluid contained 140 times as much salt as when the test started. The DOT 5's salt content did not increase at all during that same test period.

And after a month in the straight water test, the DOT 3 contained 230 times as much water as the DOT 5.

Neither water nor salt just decide on their own to migrate thru brake hoses. If that was the case, the water and salt content in both fluids would be approximately the same in identical tests. Instead, the water and salt are actively drawn thru the hose walls by the glycol fluid due to its hygroscopic nature.

GE's tests were part of a study published as SAE papers, and not some marketing campaign to sell DOT 5 brake fluid.

Water doesn't just magically "get into" DOT 5 brake fluid, so the question of whether such water would be absorbed or remain in discrete pockets is immaterial. Now, if someone pours water into the system thru the m/c, then that water would stay separated from the DOT 5 fluid. But most discussions here are aimed at people who hopefully have better sense than to do something like that.

 

metlmunchr, post: 11262726
Contrary to popular belief that all moisture enters thru the m/c reservoir, most moisture is actually absorbed thru the brake hoses.

General Electric did a bunch of tests back in the early 70's, looking at water and salt absorption of DOT 3 versus DOT 5 brake fluids. Why GE? Because they're the original developer and patent holder of most silicone based compounds on the market today, including silicone brake fluid.

GE's tests were part of a study published as SAE papers, and not some marketing campaign to sell DOT 5 brake fluid.

Does anyone know how to track down the GE study ?

Thank you

 

Glycol type brake fluid was chosen way back when because it absorbs small amounts of moisture from the air, not in spite of it, probably because old school brake systems were basically open to the atmosphere. This is by design, if it didn't the inevitable moisture buildup would pool in low points and freeze solid in the winter and boil in the summer.

 

And... Make sure your component manufacturer allows DOT 5 usage. On my car, McLeod (TOB) and Wilwood (4 portion Calipers) both warned against DOT 5.
Before you throw breakfast food at me check their respective web sites.
I drained, flushed and re-filled.

 

Hey, 364;
You could try online, but iirc, you need to be a member of SAE. When I was in school, students (Industrial Tech Auto) got a free pass, so you could get a catalog & order papers from SAE. Probably that same way now. Know a college student/prof in auto engineering or maybe a decent library? Wish I would've gotten a few papers back then... Am sure there are a lot more papers I'd like to acquire by now... .
Marcus...

 

Speaking of Wilwood, I bought my first set of Wilwood discs in 2001. They had a sticker warning against dot 5 use. I did it anyway. It's still in there 17 years later with zero problems. Now Wilwood changed their tune. They will allow dot 5.