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Brake Fluid dot 3 4 or 5 How do I tell what's in there now?

14105 Views 12 Replies 7 Participants Last post by  grandpaws 57
First off I drive dirt track... this is NOT a daily driver.

I know I can't mix 3 & 4 with dot 5 silicone fluid...

My brakes are fading... I presume boiling the fluid cause I see no leaks...

I want to change the fluid and bleed but I have been told 3 & 4 is uncompatible with dot 5 silicone fluid.

I would like to just bleed the system to replace the fluid BUT have no idea what's in there nor do I know of anyway to tell this difference with out sending it to lab... hahaha

Does anyone know how to tell the difference?

Can I just dump everything that's in the system out and go with Dot 5? or vice versa.

Thanx in advance

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Thanx a very interesting read!

Still open to how I know what is already in use.


I check to see if it will eat paint or not. Dot 3,4 and 5.1 will eat paint, DOT 5 will not.

Do not drain out DOT 5 and replace with any of the glycol type, if you do, in about a week you will have a pedal that will feel like stepping on a spring. Every rubber part will swell and get soft. I've had 2 cars in here in the last month that had that swap done, I replaced every rubber part in the system to get it to work again.

I've been told you can flush the system with denatured alcohol and put glycol in after silicone, but that scares me, I'd rather take the system apart and wash everything in brakekleen, or denatured alcohol, let it dry, reassemble the parts , then the do the swap.

I have heard you can swap up to DOT 5 after an alcohol flush, I've never seen a problem with doing that.

DOT 5 is for showcars, and I wouldn't put it in anything that was driven hard.
DOT 5.1 is supposedly better stuff, and folks who use it say it makes the brakes feel better, but I couldn't tell.

spray some rustoleum or engine paint on a piece of tin, let it dry, put a dab of fluid on it and see what it does.

Later, mikey
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I just found this: wagner "wet check" strips no idea if it's available?


Since you can’t tell how badly contaminated brake fluid is by its appearance alone (unless the fluid is full of rust or is muddy brown), the fluid should be tested unless you’re changing it for preventive maintenance or as part of a brake job.

There are three ways to check the level of moisture contamination in brake fluid:

Leica makes an optical refractometer that clearly shows the amount of moisture in the fluid. A small drop of fluid is placed in the tester, then the tester is held up to a light to read the amount of contamination. This tester is extremely accurate and shows both the percent of moisture and the fluid’s boiling point.
Chemical test strips. Ones made by Wagner Brakes (314-977-0300 or reveal moisture contamination. "WET CHECK" test strips are chemically treated to react to the moisture content in the fluid and change color to indicate if the fluid is good or needs to be replaced. A second color patch tells you what kind of fluid (DOT 3 or DOT 4) is in the system. A different type of chemical test strip is made by Phoenix Systems (888-749-7977) called "Strip Dip." The Fascar chemicals react to the presence of corrosion inhibitors in the brake fluid. A color scale rating ranges from 0 to 100. A reading of 75 or higher indiates the corrosion inhibitors are depleted and the fluid needs to be changed.
Electronic brake fluid testers actually measure the fluid’s boiling point. The test takes only about a minute and is quite accurate so you can precisely determine the condition of the fluid in a vehicle. If the fluid’s boiling temperature is getting dangerously low, replacement should be recommended to minimize the risks of pedal fade caused by fluid boil. The F300450 Brake Fluid Moisture Tester is made by Wagner Brake Products, St. Louis. MO 1-314-977-0300. A Brake Fluid Safety Tester is also made by Alba Diagnostics of Fife, Scotland and distributed in the US by ABW USA.
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Silicone brake fluid is not soluble in water, and is slightly lighter. Just pull a little of the current fluid out, put it in a clear glass of water, and swirl it around a little. If it mixes, it's 3 or 4. If it floats, it's 5.
It's my opinion that Dot 4 is adequate for most systems, but is needs to be uncontaminated, fresh, dry fluid.

I doubt your old fluid was 5, but PRM has given you a really EZ way to check- one that I've made note of (thanks, Mikey!). And jimfulco, as well- though I've never seen the results of his proposed test, it sounds "sound".

Heat is the real culprit here. That, and rubber lines (if you're still using them) will cause a spongy pedal. Anything that you can do to rid the rotor/caliper of heat will be beneficial, IMO. One of the most effective things to do, is just duct extra air flow onto them.
Dot 5 is blue so you can't mix em up.Are your brakes fading or does the pedal get spongy ?2 different problems.Could well be a different pad compound is needed.Brakes on dirt normally don't get that hot unless you are trail braking a bunch.Also are your headers close to any lines or the masters?
dirtinla said:
First off I drive dirt track... this is NOT a daily driver.
Saw the line when I re read your post.

Be aware that silicone fluid will froth if agitated. A LOT.

Used in a dirt track race car, I would think this would not be the hot tip.

I believe a conventional-type fluid, kept fresh- will be the best bet. ATE "Super Blue" (DOT 4) has a dry boiling point of 536 degrees F and a wet boiling point of 396 F. Better than the requirements for Dot 5.1 (also glycol-based).

Silicone-based brake fluid is for paint considerations, not performance, IMO. Not always blue, unless this is a relatively new development- but a good idea, either way, IMO. Except seeing contamination might be more difficult, but silicone fluid needs changed more often anyway, according to some.

MINIMAL boiling points for these specifications are as follows:
……………Dry Boiling Point-Wet Boiling Point
DOT 3 205°C…(401°F)………140°C (284°F)
DOT 4 230°C…(446°F)……..155°C (311°F)
DOT 5 260°C…(500°F)………180°C (356°F)
DOT 5.1 270°C..(518°F)………191°C (375°F)

Check the label or specifications, as these minimums can be exceeded- like in the case of the ATE "Super Blue" (DOT 4) mentioned above.
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Description and history of problem...

I have had no problems with the brakes at all until last weekend so I know it's not heat related. They have always been hard and strong. BUT I am a rookie and haven't used them much!

The car has 3 disc brakes, the right front is absent. It has 2 master cylinders with a proportioning valve to increase or decrease front to back. This valve is mechanical and doesn't proportion the fluid. There is braided lines running to each caliper and the lines are NOT soft.

So I go out on the track and it brakes great... after a few hard laps the pedal feels what I would term soft or spongy. It works but sort of deflates under pressure but will still stop. I can "2 pump" it and they catch just fine.

I presume I am boiling the fluid in the lines from hard use hence poor performance after and during hard use.

I see no leaks, the masters are full, no routing in lines have changed and the pads look good.

Fluid is amber color and doesn't smell burnt!

I am going to change the fluid and bleed and see what happens.

As always thanx in advance

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It's certainly not unheard of to have an "internal" leak past one of the MC seals.

If you've tried everything else, and heat's not an issue (or you've ducted air to help matters, and still have a soft pedal), a different MC would be an option.

I'm familiar w/the concept of using just a left side front brake to "set" the car for the turns.

However, IMO, this isn't necessarily the best way to set the car up.

I do not presume to tell you how to drive your race car! But I would suggest that you give a try to more braking while in the straight/early transition into the turn, rather than braking while actually IN the turn. And running both front brakes- you can balance the left/right brake bias as you see fit, but w/o ANY RF brake, the left brake's going to get hot, and the better you get, the hotter it'll get.

If you were watching Tony Stewart the other day, at the end of the Cup race at Pocono he was seriously in fear of running out of gas. He started coasting at about the FLAG STAND! and used no brakes (or VERY little) through the corners. Long story short, his lap times did not drop nearly what you'd have expected. And he won the race.

Sometimes you gotta slow down to be fast- charging into the corner with the brakes mashed feels fast, but you might be surprised at what the stop watch says.
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Re bleed ,check all connections for even a minute leak, check masters for any evidence of leakage.Also what chassis, springs wedge etc?.When mine was righ you would go in deep burp the throttle she would **** ,take a set and right back on the floor . No brakes needed unfortunatley when not dead on brake adjustments would have to be used to turn the car.
My experience

Ive had five that used silcone fluid. !975 f250 4x4- not driven much ,mostly towing. Flushed m/c with alkey rebuilt wheel cyl. Still working good when sold. 10-11 yrs. Toyota LC flushed out with alkey . still working good when sold. !955 race car over 150 runs {105 mph],one w/c leaked !957 ford show car Rebuilt system !988 again in 2006. I like the stuff. thanks
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