Hey guys,

I'm going to flush out the old DOT 3 from our '67 Satellite and 'upgrade' to DOT 5... when I've ejected all the DOT 3, should I flush with anything else to "rinse" it before pouring the DOT 5 in the MC and completing the bleeding process?

Maybe it's not a big deal?
I remember being told to use "de-natured alcohol" to clean out MC reservoirs.. which is rubbing alcohol.

What have you all done?
Thanks,
- Art

Having looked at a few threads online,

1. Some just flush out and refill/bleed with the new fresh fluid of whatever kind they're changing to... The theory being "only put brake fluids in your system", it's enough to flush old fluid and water droplets out.
2. A few flush with alcohol and blow it out with compressed air before filling and bleeding with fresh fluid.. The theory being "better not have ANY water or contaminants in there so clean it out first" in case you reach a boiling point.

I don't need an extreme level of performance and I monitor my fluids, I'll go with option 1.

Cheers,
- Art

Denatured alcohol is not rubbing alcohol.

Denatured alcohol is mostly ethyl alcohol cut with enough methyl alcohol to make it unsafe to drink.

Rubbing alcohol is isopropyl alcohol.

DOT 5 doesn't mix with DOT 3 which is why you want all of the DOT 3 out of there. Use DOT 5.1 instead.

https://www.valvolineglobal.com/en-eur/vehicle-maintenance-brake-fluid/

Agreed...unless your major concern is the potential paint impact, but performance wise the 5.1 stuff is right up there, and of course there are specific products that claim to go beyond this.

Thanks for the info on the alcohol..

I had a big can of DOT3 on the shelf. So I stayed with DOT3 and just bled the old fluid out until the MC was empty and then bled with fresh DOT3 until it came through all clean.. why mess with a good thing.

The old fluid wasn't dirty but brown.. I read online that DOT3 can turn brown with water absorption. So it's nice to have clean fresh DOT3 in there.

Cheers,
- Art

No matter what you use, flushing it regularly will get some nasty stuff out. I find doing a small spring flush keeps it from getting anywhere near like that pic. I’ve found doing the late model cars keeps calipers from going bad. Guys rush to drain clean 3000 mile oil out of everything and scoff at doing brake fluid. Worry and hand wring about carbonic acid in the engine and won’t do the brakes?

Yes 100% agreed

this subject has been discussed multiple times in the past.

in my OPINION. you should not flush unless you plan on completely disassembling the ENTIRE brake fluid system.
even if you "BLOW' air thru the system to get rid of the flushing fluid. some will still remain in the system. the wheel cylinders and calipers will be big holding spots.. the flush fluid will degrade the new fluid unless it's completely removed. it will compress at a different rate as brake fluid causing soft pedal problems.
just adding the new fluid forcing out the old. will still leave some old fluid in the system. at least this old fluid won't degrade the new. it won't "MIX" but they won't jell or cause compression problems. they are required to be COMPATABLE by LAW.


i have done this conversion at least 30+ times in the past. it's probably more, i lost count on the actual # it's been 15-20 years since i have done this.
i just add new fluid and pump out the old with the new.
i never has any real problems doing this.

just remember. DOT 5 retains AIR like the old stuff does water. NEVER SHAKE the bottle of DOT fluid this can create problems.
i also liked to leave the new bottle in the sun with the cap off for a few hours to help remove air from the fluid.



as others have posted. whatever you do remember to regurally flush this fluid at least every couple of yeaars.

I was always under the impression typical BF 3 was hydroscopic and the reason being it prevented any water entering the system, say from caliper immersion, mitigating that water because it would be dissipated throughout the system rather than being concentrated/stuck in one spot, leading eventually to rust/corrosion. Of course, that hydroscopic aspect would gradually lower the fluid boiling point, and eventually once enough water was absorbed rust would soon follow. The newer 5 Fluids resist water absorption, but that does not prevent the downsides if when it happens but maybe speed up the rust process.

Agreed on how the fluids absorb or not the water.

But the fact that water gets in anywhere other than the master cylinder lid indicates that fluid can get out.

In other words, the system is already compromised and fluid type becomes irrelevant.

Logically you are correct, but it's a system designed as you mentioned for internal pressure, but not against outside pressure getting in, and I am not sure how much water pressure occurs from hitting a water puddle at say 70 mph.

Small follow-up to the thread and my last post: I recently went through a bit of this "purge the old fluid from the system" undertaking. I wasn't sure what was in there to start off with, seemed to remember doing DOT5 (to avoid the potential paint damage), but upon testing the stuff would in fact mix and not stay separated...so I concluded DOT x.

Anyways...from there I wanted to go to the best I could find at the local parts store. Ended up picking up Bosch ESI632N, which is a 5.1 fluid and claims to be compatible with all the other ones (with the exception of pure DOT5).

Take a look at the attached spec sheet...I used that, so far no problems, brakes are awesome!!!

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 ̊C. (401 ̊F.).

(b) DOT 4: 230 ̊C. (446 ̊F.).

(c) DOT 5: 260 ̊C. (500 ̊F.).

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

So, did "A recent change" now require miscibility that did not exist previously?
Lack of "miscibility " may not in most cases effect actual braking I suspect (even if it did exist) which seems to be the antidotal answer here.
They require purple for a reason in 5 and not 5.1 for a reason, and I suspect it's not for protection of paint.

I started using Dot 5 in 2004 on all new system's no problems so far. Maybe i need 1 more year testing?
I also in 2004 started using it in some classic cars. But when switching pulled as much old stuff put with mity vac intill ckean purple and no bubbles. Also maybe 19 year's is not a good test?

I don't think the big issue isn't whether the fluids mix, hydraulically speaking it doesn't matter.

The problem might arise with fluid compatibility with the seals and soft parts. Probably a bigger issue when new fluids came out in the 70s, not very likely with today's rubber compounds.

If I was changing over, I'd make sure to clean out all the old fluid, to the point of disassembly or replacing parts. One doesn't have to, but why hamstring the system with old fluid?

Thanks guys, yeah, I stayed with DOT3 in this car.

I switched our '65 Satellite over to DOT5 when I converted to two-circuit MC and the entire brake system was refreshed with new lines, brake cylinders, hoses.



Yeah, this is where I have landed with almost all fluids.. A minor flush or refresh is a lot easier and cheaper than the deferred cost of excessive corrosion or repairing the damage.
Online information says that DOT3 will turn brown with age and increasing water content.
The seller of this car drove it regularly, but not far or long, over the past 4 years.
The brown brake fluid was probably older than that.

Cheers,
- Art

Thanks, that is good stuff..