Brake Issue Using Dot 5

[Some Car Guy]

I don't think the NHTSA in its Federal Motor Vehicle Safety Standards is parroting when they advise:

"If your vehicle contained a brake fluid other than DOT 5 in its brake system, we recommend that the old fluid be flushed completely out of the brake system, before being replaced with DOT 5. This is necessary to ensure that the DOT 5 brake fluid does not mix with any other brake fluid type."

That doesn’t explain all the guys saying it’s the end of the world and you will have to”problems.” The ones saying you have to alcohol flush and pray. The ones saying 5 will destroy parts, like a shop I know of that thinks it killed two masters in cars they converted. It doesn’t explain that guy you linked saying 5 is the one that will kill paint. Or the ones saying it will cause a soft pedal, which is 100% false and a sign that person didn’t bleed it right. That simply says to flush the system.

 

[Mariposa Mike]

Thanks for all the good info and reinforcing my belief the Dot 5 is a good substitute. This is my first experience with it. Got the new wheel cylinder in today and bled the brake. Took it for a drive and all was good. BTW, I had a lot of Dot 5 on my brake shoes but laquer thinner and then sanding them brought them back. Going to a car show tomorrow and did not do the other side yet but will do so next week. Then check the fronts which I believe have been serviced since the rears were done. The parts in the front brakes are shiney unlike the rear. But who knows how long the front cylinders have been in there. If I get squeaks from the rears I will have to pop for new shoes. Those were not in stock when I got the cylinders.

I noted the shoe springs which are red and yellow were reverse what a previous post showed on this site. The yellow is a little longer and a little more tension that the red which is one shown on the shoe with the self adjuster cable. So I reversed them from what I took off. I have never known what the reason was for the different colors. 66 factory manual does not explain either. If anyone knows the answer to that one I sure would like to be enlightened.

 

[Photon440]

That doesn’t explain all the guys saying it’s the end of the world and you will have to”problems.” The ones saying you have to alcohol flush and pray. The ones saying 5 will destroy parts, like a shop I know of that thinks it killed two masters in cars they converted. It doesn’t explain that guy you linked saying 5 is the one that will kill paint. Or the ones saying it will cause a soft pedal, which is 100% false and a sign that person didn’t bleed it right. That simply says to flush the system.

I don't know why someone states that it will harm paint, we all know that silicone won't hurt it.

Soft pedal stories arise from the fact that DOT 5 is prone to dissolving or entrapping air bubbles in solution far more than the other types, which is why DOT 5 isn't recommended for ABS systems as the pulsating pressure will release the air and cause foam. Aeration will lead to soft pedals, as some people have noted. Not at all a problem for mild street use or car shows where people prefer the paint safe fluids.

Wilwood, who knows something about braking, does not recommend DOT 5 for racing applications due to foaming and aeration causing spongy brakes. And while they do sell calipers (GNX4) designed for DOT 5, they say they should not be used with other types of brake fluid, similarly their standard calipers (GNX5)for DOT 3,4 and 5.1 are not to be used with DOT 5. They do sell a DOT 5 fluid, which they recommend for Harleys and classic cars, but also point out that:

Wilwood FIVE DOT 5 brake fluid is not compatible
with glycol-based DOT 3, DOT 4, or DOT 5.1 fluids and
will turn to gel if mixed, resulting in brake failure.

Another company that doesn't agree with Ehrenberg.

 

[Some Car Guy]

I’ve read a lot of posts from guys having trouble bleeding all sorts of brakes. All types of fluid. If you can’t get a system bled, it doesn’t matter what you poured in. You’re gonna have issues.

I don’t know who is having trouble racing with 5. It has a higher boiling point than 4. Green brick is a good example of one of our cars being pushed as hard as any of us have.

 

[Photon440]

I’ve read a lot of posts from guys having trouble bleeding all sorts of brakes. All types of fluid. If you can’t get a system bled, it doesn’t matter what you poured in. You’re gonna have issues.

I don’t know who is having trouble racing with 5. It has a higher boiling point than 4. Green brick is a good example of one of our cars being pushed as hard as any of us have.

SAE J1705, Appendix A, A.2.2.8, states “Air Solubility – It has been reported that dimethyl polysiloxane fluid, which is a major part of silicone-based, low water-tolerant type brake fluids can typically contain dissolved air at a level of 16% ±3% by volume at standard temperature and pressure. This compares with a typical level of 5% ±2% by volume of dissolved air for glycol ether based type fluids.

An increase in brake pedal travel may be experienced under severe operating conditions, especially at higher altitudes and high temperature conditions. "The term “dissolved air” (air absorbed from the atmosphere) should not be confused with the term “entrapped” or “free air” since their effects on brake system performance can be entirely different. Air that has been absorbed from the atmosphere does not result in an increase in fluid or system volume, whereas entrapped air or free air does occupy system volume and can be easily compressed when force is applied to the system.“

The SAE standard continues, “A.2.2.8 – Compressibility – Silicone based brake fluids are more compressible than conventional brake fluids and the difference is magnified at higher temperatures.” Silicon-based brake fluids are described by DOT 5 (not to be confused with DOT 5.1), which should never be used in a racing vehicle due primarily to its compressibility.

 

[YY1]

This is my 10 year anniversary for converting the 73 to DOT 5.

No issues other than an ever so slightly more spongy pedal.

I used Brakleen to flush the chassis and rear axle hard lines and distribution block.

Front lines and all hoses, cylinders and calipers were replaced.

 

[zyzzyx]

I don't know about how all of you bleed your brakes, but I prefer to vacuum bleed them at the wheel cylinders.
There are some inexpensive ones on E-Bay. I take out the bleeder screws and give them a nice coat of heavy
grease to keep from sucking air from around the threads. Then I bleed each one starting at the R.R., then the
L.R., then the R.F., then the L.F. It's the easiest and most fool proof way to get all of the air out. Just my 2 cents.

 

[dvw]

Been using Dot 5 for over 45 years. 3 cars currently. The only corrosion issue I ever had was when the car sat untouched for 10 years. By that time it had used Dot 5 for over 30 years. My 2nd street car has had Dot 5 for 22 years. Brake system has never been touched in that time. Racecar has had Dot 5 13 years, same story. Brake fluid doesn't cause hydraulic parts failure, corosion and age do that. Not to mention off the shelf new parts that have internal rust. If you don't disasemble the new stuff? You'll never know. If y the car is regularly driven, the brakes will easily get hot enough to boil off any water. Ho do you know if you have water in the system with Dot 5? Easy, when water boils it becomes a gas. Gasses are compressible. Thus a soft pedal. It is a little harder to bleed, go slow. Plenty of false info out there. People blame failures on many things. Most often because they don't understand what they are working on.
Doug

 

[Some Car Guy]

SAE J1705, Appendix A, A.2.2.8, states “Air Solubility – It has been reported that dimethyl polysiloxane fluid, which is a major part of silicone-based, low water-tolerant type brake fluids can typically contain dissolved air at a level of 16% ±3% by volume at standard temperature and pressure. This compares with a typical level of 5% ±2% by volume of dissolved air for glycol ether based type fluids.

An increase in brake pedal travel may be experienced under severe operating conditions, especially at higher altitudes and high temperature conditions. "The term “dissolved air” (air absorbed from the atmosphere) should not be confused with the term “entrapped” or “free air” since their effects on brake system performance can be entirely different. Air that has been absorbed from the atmosphere does not result in an increase in fluid or system volume, whereas entrapped air or free air does occupy system volume and can be easily compressed when force is applied to the system.“

The SAE standard continues, “A.2.2.8 – Compressibility – Silicone based brake fluids are more compressible than conventional brake fluids and the difference is magnified at higher temperatures.” Silicon-based brake fluids are described by DOT 5 (not to be confused with DOT 5.1), which should never be used in a racing vehicle due primarily to its compressibility.

That’s really cool. Use what you want. No sweat off my balls. You seem to be caught up in this and are bothered by other people having success with dot 5.

 

[Some Car Guy]

I don't know about how all of you bleed your brakes, but I prefer to vacuum bleed them at the wheel cylinders.
There are some inexpensive ones on E-Bay. I take out the bleeder screws and give them a nice coat of heavy
grease to keep from sucking air from around the threads. Then I bleed each one starting at the R.R., then the
L.R., then the R.F., then the L.F. It's the easiest and most fool proof way to get all of the air out. Just my 2 cents.

I’ve been using a cheap one man bleeder kit for about thirty years now. Way easier with a helper, but it works every time. The 5 bled easy as 3 and 4. I just went slowly and zero issues.

 

[Photon440]

That’s really cool. Use what you want. No sweat off my balls. You seem to be caught up in this and are bothered by other people having success with dot 5.

I'm not caught up in it at all, just pointing out some things that interested people might want to know. If you read all the other replies, you'll note that a soft pedal has been mentioned in DOT 5 systems by some users on here. If it works for you, great.

 

[AR67GTX]

I have speed bleeders on my four cars for simplified bleeding. They work great. I have a Motion pressure pot bleeder, vacuum gun, and a reverse pressure bleeder also. They all sit in their drawer now as none of them compare to the simple use of speed bleeders. Just be sure to crack them open only about 1/4 turn so as to not wear out the thread sealer on them. But after several bleeding jobs I just pull them and add a little thread sealer to them and they continue to do their thing.

 

[dvw]

I'm not caught up in it at all, just pointing out some things that interested people might want to know. If you read all the other replies, you'll note that a soft pedal has been mentioned in DOT 5 systems by some users on here. If it works for you, great.

The only case I wouldn't use Dot 5 is road racing or circle track. As the air/moisture content could be an issue in repeated high speed brake performance. I can tell you from experience I've run on a few of the shortest dragstrips around, over 147 mph in the 1/4. No issues what so ever slowing down a 3400 lb car.
Doug

 

[Mariposa Mike]

This has been interesting and informative feedback. I would still like to know about the color/purpose of the springs but maybe that will be answered another time. A long time mechanic in town might be able to give us some input that I can post later. I drove 40 miles one way (and back) to a car show yesterday and had to apply the brakes hard a couple times for inconsiderate drivers. They are much better now with at least the one rear side working as designed. I had been blaming the lack of front disc brakes for the poor performance. Thanks again for all the info and related experience with Dot 5. I feel confident now to continue using it.

Mike

 

[Bird 426]

I have DOT 5 in all three of my cars, one is a summer daily driver, except if it rains. Never looking back at that moisture paint eating crap from here on.