Brake Fluid: DOT 3 v. DOT 4

[ARCHINSTL]

4wdchico just made the following post in another thread:
I don't consider my brakes fully bled/flushed until I put at least a full quart of fluid thru the system. Do that every year or two and the odds of having a failure in the hydro portion of your brake system goes down massively. Also, I prefer to use DOT 4 brake fluid, it has a slightly higher boiling point, but the real reason I like it is that it has higher anti-corrosion package specs. DOT 3 & 4 fluid are fully compatible.

I noticed very dirty fluid in a post I made about brake fluid:
http://www.tercel4wd.com/forums/viewtop ... ake#p42634
Without going to the preceding thread - after 4 years, the DOT 3 fluid in the rears was very dark and both front bleeder screws were clogged and had to be removed. And in 2006, I'd run over two quarts through when I did the complete (save lines and MC) brake job (what was in there was espresso).
Now, granted, STL is a very humid area.

Are Tercel/'80s Toy systems more susceptible to moisture absorption than others? My '88 Dodge/Mitsu p'up, while a POS real rustbucket in every other conceivable way did not have espresso fluid, even though admittedly neglected - of course, its brake lines rusted through and I had to replace all of them...

So - should we use DOT 4? The cost is not that much more than DOT 3.
Tom M.

[shogun]

i use ate dot4 synthetic something or other i had left from the autocross car, it has been more stable in hard braking, but its a b$%%tch to bleed the brakes dont have a clue as why, as far as moisture retention i use a viton oring inside the cap and that seems to help ( this one was free we make them at the shop, otherwise pretty expensive) i wont go back to dot3 or upgrade to dot 5 any time soon, so its a good and cheap upgrade

[splatterdog]

Unless you are racing, DOT4 is a little overkill. A good DOT3 can spec out pretty close to DOT4 also. On an old T4 it would be mostly a feel good upgrade and any improvement noticed would be from air that was already in the system or you just think it works better. While it is likely a rare occurence, a Dot 3 system may not be compatible with DOT4 and it's extra additives. When in doubt, use what the car maker says.

Only motorcycles and Euro cars require brake fluid higher than 3. Some take DOT4+ or even low viscosity DOT4 that allows faster performance on ABS/TCS. It should be noted also that most Euro manu's recommend/require new fluid every 2 years. Certainly not condoning it, but I have seen cars go to the grave with original fluid, and still stop OK. With ABS/TCS, that can be risky/expensive. Most fluid doesn't get flushed unless there is other work being performed that requires bleeding. Kinda goes in the same category as waiting to change trans fluid because it's not working correctly. Maintenance is always cheaper than repair. I'm pretty sure at least one of my T4's, or any other old turd I've ever had for that matter came with factory brake fluid. Par for the course on $100 beaters....

Tom, it's likely you had some goop on the bottom of the reservoir. Unless it's spotless inside, the coffee stain will return. Most modern reservoirs do not clean easily. Either remove the res and clean it or just give it a yearly flush. Air/moisture gets in no matter what you do. Master cyl caps are slightly vented. Air can even work it's way thru brake hoses! BTW, I really like the power bleeder I added to my collection of tools. I'm even more brake fluid maintenance minded after getting the right tool for the job. Sure beats vacuum bleeding. I'm not surprised your Toyota lines lasted longer than the Mitsu. I saved the brake lines from my parts T4 that the unibody had rusted away. Most fittings even spun by finger after cracking loose and no torch was needed. I've had 3 year old Mopars that needed heat on every single fitting to come loose(contaminated with PS fluid before it's first brake job). Maybe the D50's lines were a result of the Mitsu/Mopar marriage. haha

Shogun- I hope that fluid lying around wasn't very old. Shelf life is pretty much over after the cap comes off.

One quart should be sufficient to flush a T4, unless it's nasty. Some reservoirs nowadays hold almost that by themselves!

[Petros]

I would say Splatterdog is correct. Even in a pretty severe braking environment, hilly terrain as we have here in the PNW, it is doubtful you would ever over heat the brake fluid in street driving. It is not like we will be pulling 10,000 lb travel trailers in our Tercels. Even the occasional autocross or club racing (as if the Tercel is even remotely competitive) would not heat up the brakes for very long for you to notice the difference between Dot 3 or 4. Those flimsy 11mm thick solid front rotors will give up long before the DOT 3 fluid.

Flushing the fluid every 2-3 years or so would do more to prevent corrosion and espresso brake fluid than using DOT 4.

Use dot 4 it if you like, some on this list are "oil snobs", why not brake fluid snobs too?

[shogun]

well i have braided lines, and i drive the hell out of my car, usualy on the roads i drive in my 85mph speedo is in the regions there there are no numbers, but in brakes is the only place i refuse to cheap out on, but as you guys said normal city driving no difference at all, maybe that the pedal felt not as squishy as the other fluid, the last dot 3 i used was motul and it is pretty good, but this one is much better, but it helps to change the fluid regurlarly i do it every 4 or 5 months

[Petros]

I just ran across this bulletin about mixing brake fluid and remembered this thread. it says "DO NOT mix" and to flush the system if you did mix them. Use only what manufacturer's recommends.

http://cardone.com/english/club/Product ... 0-0006.pdf

"Choosing which type (DOT 3, 4, or 5) of brake fluid for your brake
system. Does it really matter?

YES! It’s very important– the fluid specified by the original vehicle
manufacturers must be used. DOT 3 & 4 brake fluid is a mineral
based fluid. DOT 5 is silicone based. Never mix the two types. DO
NOT use DOT 5 in a vehicle equipped with ABS (Anti-Lock Brake
System). Foaming of the fluid will occur due to the pulsed high
pressure action of the ABS system under braking. To determine which
fluid should be used for your vehicle, simply consult the shop manual
or look on the master cylinder lid or reservoir body.

If two different brake fluids have been mixed, the brake system should
be flushed, and fresh brake fluid recommended by the vehicle’s
manufacturer should be installed."

[4wdchico]

My brake fluid of choice for several years was Valvoline Synpower. Said for dot 3 and 4 right on the bottle. It was cheap and widely available and had better than standard wet and dry boiling points. Sadly, it is no more. The link below shows Valvoline's current offering in a brake fluid that is rated both dot 3/4. It's boiling points are not as good as the old Sypower was.

http://www.valvoline.com/products/consu ... ake-fluid/

So, after doing a bunch of research inspired by this thread, I'm going to order up a few liters of the below linked ATE performance brake fluid and do the annual flush on all my rigs that is due around the first of the year. BTW, I flush my brake fluid on a cold dry day in the winter as cold air can hold only a fraction of the moisture that warm air can.

http://www.tirerack.com/brakes/accessor ... .jsp?ID=22

Then, next year, my rigs will get a flush with the blue version of the same product (linked below) as the blue color will make it easy to tell when the new fluid is flushed thru the system.

http://www.tirerack.com/brakes/accessor ... .jsp?ID=21

Overkill? Yes, but that is my style when dealing with brake systems.

[shogun]

i use ate in all the race cars and my personal cars, plus they sponsor so i get it for free!