Anyone try DOT 4 Synthetic Brake Fluid? (Page 1/4)
Dennis LaGrua OCT 13, 09:55 PM
Many recent brake systems use DOT 4 Brake Fluid. Its synthetic and its advantage is that it supposedly doesn't hold moisture like std DOT 3 brake fluid. If a conversion was made to this fluid, it would entail draining and bleeding out the old fluid and introducing new DOT 4 fluid into a clean system. I believe that DOT brake fluid is a silicone based fluid.
Has anyone tried using it and did it work correctly? Do the caliper seals and the Master Cylinder hold up using it ? There must be some advantage to using it but in a Fiero or older automobile it may not work well or will it?
Thoughts on using it??

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pmbrunelle OCT 13, 10:09 PM
Ogre explained this in his Cave:
http://web.archive.org/web/...fierocave/brakef.htm
Dennis LaGrua OCT 13, 10:32 PM

quote
Originally posted by pmbrunelle:

Ogre explained this in his Cave:
http://web.archive.org/web/...fierocave/brakef.htm



I read that but it doesn't touch on my main point of whether all the seals MC/Wheel and the switch will be compatible with the DOT 4 fluid. I know guys have tried the silicone fluid in classic cars and it destroyed the brake switch and wheel cylinder seals. The Fiero has the brake switch on the pedal but also has a switch on the proportioning valve. My question is will the sensing elements in that switch be hurt by silicone fluid?
pmbrunelle OCT 13, 10:47 PM
DOT 4 is glycol, just like DOT 3 and DOT 5.1.

DOT 5 is the silicone fluid.

Many (most?) soft brake parts are made from EPDM. EPDM should be OK with silicone.

The prudent course of action when dealing with unknown soft materials is to soak the mystery parts in your fluid of choice, and then see if swelling or any adverse reaction occurs.

A one month soak should* be more than enough time to uncover any potential problems.

*I can't offer any sort of guarantee on that.
Blacktree OCT 14, 02:22 AM

quote
Originally posted by Dennis LaGrua: If a conversion was made to this fluid, it would entail draining and bleeding out the old fluid and introducing new DOT 4 fluid into a clean system. I believe that DOT brake fluid is a silicone based fluid.


This is incorrect. DOT4 brake fluid is chemically compatible with DOT3 fluid.
theogre OCT 14, 03:02 AM

quote
Originally posted by pmbrunelle:
DOT 4 is glycol, just like DOT 3 and DOT 5.1.

DOT 5 is the silicone fluid.

Correct.
DOT 4 fluid is "better" then any 3 fluid for normal street use and off road like mud crawlers.
You find 3 w/ "higher" boil point then 4, even 5 and 5.1, but is only for Dry Boil. Many of these are "racing fluids" that expect to get change often.

You can run DOT 4 in cars call for 3 but Not other way around.
If you read "expert level" doc's all say the same... Can run 4 or 5.1 in MC lid calling for DOT 3. Many recent vehicle calls for DOT 4... Can add 5.1 but not 3. Rarely car may call for 5.1 when true can't use 3 or 4.
Some brands like Valvoline combine DOT 3 & DOT 4 in one product. Use them if you don't trust DOT4 label products.

I've been doing this for 20+ years and never had any problem. BUT If a vehicle has True ABS, I won't switch DOT #. Is very likely Technically Safe but ABS "Black Boxes" are so expensive is not worth to change DOT # and have ABS problems and people and dealers saying you did something wrong to Void a Warranty etc. ("Fake" ABS are used in some trucks etc w/ only an "load sense" prop valve tied to the rear axle. They are way too dumb to notice DOT # and related specs.)

Topping up the MC tank w/ 4 is no point... Only time you hope it makes a dif is when you "flush" old dirty fluid out until bleeders see clear fluid. Best after you replace hoses and/or calipers when you can empty calipers or have new dry calipers and can purge old fluid out of lines before connecting new parts.

I have a boil tester showing actual boil point of fluid in a car and many cars have very wet brake fluid and boils at very low temps. (This tool cost several hundreds of $.)
The Only time I see Dry boil is when just test a new bottle or very new cars not driven much.
Many times the Second New fluid is mix w/ old fluid the new D3 is so wet can't reach the wet spec on bottle or NHTSA's FMVSS specs. That's ever after you drain most old fluid for major repair/rebuild of the system. D4 handle old fluid better new D3.

Using DOT5 Silicone in any DOT 3 4 or 5.1 is bad on many levels. Won't make seals to swell like oil will but will cause problems, some are covered in cave page.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

pmbrunelle OCT 14, 08:55 AM

quote
Originally posted by theogre:
Topping up the MC tank w/ 4 is no point... Only time you hope it makes a dif is when you "flush" old dirty fluid out until bleeders see clear fluid. Best after you replace hoses and/or calipers when you can empty calipers or have new dry calipers and can purge old fluid out of lines before connecting new parts.



From an inventory-control standpoint, I find it good to only stock the highest-spec fluid I need (such as DOT 4). This way I don't need to stock different bottles.

Also, once a bottle has been opened, it's best to use it quickly, before it picks up humidity. So keeping just one kind of brake fluid reduces the number of opened bottles I have.
Blacktree OCT 14, 10:58 AM
My thoughts exactly. The DOT4 can also be used in clutch hydraulics. I see no reason to stock DOT3 fluid anymore.
theogre OCT 14, 02:12 PM

quote
Originally posted by pmbrunelle:
From an inventory-control standpoint, I find it good to only stock the highest-spec fluid I need (such as DOT 4). This way I don't need to stock different bottles.

Also, once a bottle has been opened, it's best to use it quickly, before it picks up humidity. So keeping just one kind of brake fluid reduces the number of opened bottles I have.

True but quoted why?


quote
Originally posted by theogre:
Topping up the MC tank w/ 4 is no point... Only time you hope it makes a dif is when you "flush" old dirty fluid out until bleeders see clear fluid. Best after you replace hoses and/or calipers when you can empty calipers or have new dry calipers and can purge old fluid out of lines before connecting new parts.

Again, Topping up the MC tank w/ 4 or any other is no point to think will change boil point because not enough new fluid.

Open bottles have "wet air" in them and pulls water from air after because of the cap mostly. Cap and its "Gasket" are not made to seal long term.
Vs. Many MC caps have rubber to seal and allow fluid drop so never get fresh wet air on top of fluid. MC Caps have vent(s) to allow air equalization for the rubber but vent air doesn't make connect w/ fluid unless rubber is bad.

For "inventory..."
For MC top off and other small jobs only use small bottles for this reason.
Only use 1 quart bottles for major work that you use it all at once.
Even then don't keep unopened plastic bottles of brake fluid in private inventory for months to years.

⚠️ Warning: Brake fluid is a HAZMAT and illegal to dump in most places. For "home use" can go to local HAZMAT drop-off many places often have only a couple times a years. Contact city etc solid wast management group even if normal trash is pick up thru 3rd parties.
Spadesluck OCT 14, 04:13 PM
Honestly if you have not drained/flushed your brake fluid in your Fiero now maybe now is a good time to do it, then switch it over to DOT4.