Just to set the record straight before getting anymore posts from the proponents of dot 5 that bad info is being passed around on this posting. I asked some questions. I didn`t post the questions to start a debate or a argument. My brakes felt odd. I removed the master cyl cover and was struck by the purple color of the fluid. I did no research on dot 5 before posting other then how to ID dot 5 fluid and then I posted my question here. I never heard any rumors or read any bad info as I have never been interested about finding out about dot 5 until I bought this car. I never had a car with dot 5 before. The dot 5 was installed by the previous owner. I was curious if dot 5 had any characteristics different from dot 3 or 4 or if I had to look for another problem on my car. I got the answer. The dot 5 will stay in the car and will not be removed. I will have to ask questions here as I am not a trained or seasoned mechanic and there are some smart individuals here. I find it hard to believe my questions can be turned around into a dot 5 bashing. It wasn`t meant to hurt anyone's feelings or disrupt anyone's day.

My cars are a mix of DOT 3, 3-4 and 5.
Each one works just fine with the OEM fluid they came with.
Just use it consistently, keep it refreshed and don't mix.

- The '67 Satellite is driven in regular passenger street conditions on DOT 3, and is just fine.
- The '82 Alfa Romeo track racer is abusive on brakes and bearings, but never had an issue on factory spec DOT 3-4.
- The '65 Satellite was restored and converted to a two-circuit MC for regular street use. I put DOT 5 in it from the get-go, I'm thankful I made the choice, cuz I spilled some on the paint and it didn't eat into it. The only issue I had with the brake feel was traced it to the automatic brake shoe advancers not working properly on the front. It wasn't the DOT 5.

Cheers,
- Art

Still seems to be some misinformation. My understanding on this very well-worn topic was that DOT5 absolutely is mixable with DOT3 or 4, since that is a legal requirement for any brake fluid. But just because you can, why would you - it costs more, and you wouldn't get the benefits like it being kind to paint etc.
Also, it's common to find the brakes a bit more difficult to bleed (i.e. start with a slightly more spongy pedal), but once properly bled should be absolutely fine.

I originally re-did my 1967 Barracuda in 1980 and put DOT 5 in it. Still in it today. Just finishing up a '66 coronet disc brake conversion and DOT 5 went right into that as well (from the same jug that I bought in 1980).

No issues, no horror stories (and no gunked up an plugged lines)

in my experience with bleeding brakes, no matter what fluid is used, the most common problem with not being able to get all the air out of the system [not counting upside down calipers] comes from guys pumping the living wizz out of the pedal before cracking the bleeder. this will cause foaming of the fluid. if a guy just lightly pushes down, open the bleeder, close the bleeder, release the pedal, no foaming happens. rinse and repeat a couple of times, done. if by yourself, lightly crack bleeder, put a tight fitting hose on the bleeder, then submerge the hose into a jar or can with clean fluid. lightly stroke pedal, rince, repeat several times per wheel, done. this has worked for me for many, many, years.

DOT 5.1 is often confused with DOT 5, DOT 5 is NOT COMPATIBLE with anything, DOT 5.1 however is...

True dat but so what?

That's simply not true and that chart is somebody's wet dream. The definition of "compatible" is two things able to exist or occur together without conflict.

As stated earlier, in order to receive DOT approval, all brake fluids must be able to coexist in the same system with no ill effects.

I am reading directly from a bottle of DOT-5...
"This product is not compatible with DOT-3 or DOT-4 brake fluid."

Maybe it's a CYA on the part of the manufacturer, BUT, I have now changed my mind...

Joe

Sure... you could add salad dressing and mineral spirits along with DOT3/4 and DOT5 if you wanted to, but would you want that in your system?

Whom am I to believe?, you or the brake/brake fluid manufacturer(s)?

Make me a believer, some me some data on DOT5 and DOT3/4 mixed in the same system with no "ill effects"... mechanical effects, not chemical...

Have used in my 56 300 B since restoration in 1986. Zero issues outside of normal lousy standard 1956 drum brake performance. Good for one panic stop or less at 60 mph. What is worse than standard drum brakes is the fact of only one reservoir for both front and rear brakes.

Dot 5 is worth the price of admission if for no other reason is that it will not damage your concour paint job if you blow a hose or spill on paint.

Keep in mind that the disclaimers are written by lawyers, not engineers.

Update: It was the master cylinder that was bad. I put a new one on and the pedal feels like it should now. Thanks for the help.

Glad you got your problem fixed.


Now, do you see why I love this topic?

Glad to hear it but...
WOW people, WTH.

It is good stuff but it definitely is tougher to bleed than regular stuff. I personally prefer Castrol SRF. It's a little pricy but has all the upside of dot 5 and none of the down side. Dot 5 doesn't hold any water so you have to be careful if you don't have stainless lines. Water accumulates and can cause rusting in the system. Not likely in a well maintained vehicle in a more stable climate but can cause issues if you live and drive where the temperature swings a lot and you don't change out your fluid every few years.

I'm sorry.
I live in Wisc as well.
How does moisture get in your lines?
I have never had that problem.
My junk gets normal maintenance at best.
Likely not what they should.
I have a couple 70's trucks I drive year round with zero brake fluid issues.
I am lazy about maintenance with these trucks and use the cheapest crap on the shelf, in the system.
The original lines lasted several decades and I expect them to do it again.

I've not seen anything to make me change my mind on what I stated. It's a legal requirement for all DOT brake fluids to be able to mix. but you wouldn't want to because you lose the extra benefits you are paying for, so no surprise that the vendors say do not mix - they don't want you paying extra then still finding problems. (I'm sure they wouldn't mind selling larger quantities either!)

Surprised E-Berg has not chipped in:

Tech Question
Gary Boak, Chilliwack, BC, Canada, 1969 Dart Swinger 340

I notice in the April 04 issue you say that DOT 5 brake fluid can be used without flushing the system. Everything I have heard and read states that Dot 5 does not mix with anything except DOT 5. When switching to DOT 5 are you not supposed to use new rubber?

Gary-

Another old wive's (or Mopar Muscle) tale. First, realize that DOT specs don't specify the composition of the fluid, the rating relates only to the boiling point. So, therefore, it would be possible to have DOT 3 fluid that's silicone, and DOT 5 that's not (and this latter combination does exist.) These specs are covered in detail in Federal Motor Vehicle Safety Standard section number 571.116, which is part of the Code of Federal Regulations, #49, Chapter V, see for yourself at:

Code of Federal Regulations, #49, Chapter V
Here's an excerpt from the law on boiling points:

Equilibrium reflu point (ERBP). When brake fluid is tested according to S6.1, the ERBP shall not be less than the following value for the grade indicated:

(a) DOT 3: 205 ÌŠC. (401 ÌŠF.).

(b) DOT 4: 230 ÌŠC. (446 ÌŠF.).

(c) DOT 5: 260 ÌŠC. (500 ÌŠF.).

A recent change to the law specifies that non-silicone fluid meeting DOT 5 temperature specs. be labeled DOT 5.1. All DOT 5 fluid must be purple in color, all other grades must be clear to amber.

The baziilion pages of the specs relate mostly to boiling points, viscosity, and the fluid's effects on rubber (swelling), as well as testing procedures. But there's also much written about compatibility. What has probably caused the confusion is that DOT 5 fluids are tested differently than other types, but these tests apply equally to silicone and non-silicone fluids. Subchapter S6.5.4 addresses miscibilty, specifying that the fluid being tested must mix with a standard type fluid, and this miscibilty test DOES apply to DOT 5 fluids, and can't gel, swll cups, etc. when mixed. So there!

The Society of Automotive Engineers (SAE) also has detailed specs: J1703 and J1705.

It's true that much has be written saying that silicone based fluids cannot or should no be mixed with other types, this is that old myth-perpetuating deal. Nowhere can I find a scientific study or analysis to back this story up - do a Google search yourself if you don't trust me.. There's only been two studies on this that I'm aware of: Dow-Corning, the leader in silicone brake fluids (possibly the only true USA manufacturer), did a detailed study almost 30 years ago, wherein a system was haphazardly swapped from DOT 3 to silicone, with the intent of leaving a significant portion of the fluid UNchanged. The system passed all DOT tests easily. The second test is less scientific, but, to me, more significant: Yours truly has been using DOT 5 silicone in every car I've owned or serviced since approx. 1978. I have never flushed a system! I have, in some cases, bled out most of the old stuff, in other cases, I've just topped up a DOT 3-filled system with silicone. Cars serviced by me in this fashion have stopped will from speeds over 160 MPH. I've never had a stuck caliper (or wheel cylinder) pistion since making this change universal in my fleet - even in cars stored for long periods. I've also never damaged pain from a brake fluid spill. Come to my garage - you will find 4 or 5 bottles of DOT 5 silicone, and zero of DOT 3 or 4.

On your Dart, do what I do (and say): bleed out as much of the old garbage as you can, until you see purple at each bleeder screw. And don't worry about it!

End of story.

Rick Ehrenberg

Wow, there you go right there. States law, specs, everything. Definitive answer.

But wait, there's more! In 6 months to a year this will come up again.

See ya then!

FWIW (probably not relevant to this conversation), in the late 80's/early 90's the Air Force converted the brake fluid in our munitions trailers to "silicone" brake fluid (dot 5). The TCTO (time compliance technical order) required the systems be flushed with denatured alcohol prior to introducing the dot 5 to the system. Was it necessary? I don't know, but that was our instructions back then. I provided this input for folks that want to convert to dot 5 but are leary about mixing the fluids...