Brake fluid

[daved]

Looks like I need to top off my brake fluid. Went to the auto parts store yesterday. They have DOT 3, DOT 3-4 and DOT 5 (silicone) Know I don't want the DOT 5. Haynes manual says SAE J1703C or better. Using Goggle I can't find SAE J1703C, do find SAE J1703 and am thinking it is similar to DOT 3. Anyone know for sure if I can use DOT 3?

[bradartigue]

Use DOT 4. Sold everywhere. It may even say DOT 3/4. DOT 5 will cause you problems; synthetic will cause you problems.

[daved]

Thanks for the answer.

[Rambo]

Sorry to steal this topic but i am also having issues finding the right fluid. I need to find a brake fluid for my 79 but am having trouble finding a good quality fluid. I know i need a Dot 4 non-synthetic but after browsing the web and going to the local parts store all i can find is auto zone brand dot 3. Pretty much everything now is synthetic. Does any one have any recommendations?

[bradartigue]

http://www.amazon.com/ATE-706202-Origin ... RSCYB8A96S

ATE Typ 200

[mpollock]

Actually, unless you are using mineral oil in your brakes ALL brake fluid is synthetic. The difference is that DOT5 is made of silicon and the other DOTs (including DOT5.1) are made of Glycol formulations.

[Topless]

Use DOT 4. Sold everywhere. It may even say DOT 3/4. DOT 5 will cause you problems; synthetic will cause you problems.

My '79 owner's manual specifies Dot 3.
Would there be a reason to vary from this and use Dot 4 instead?
Will using Dot 4 cause any problems?

[18Fiatsandcounting]

Will using Dot 4 cause any problems?

No. DOT 4 is a higher performance version of DOT 3, and DOT 4 was not widely available for regular vehicles back in the 1970s or 1980s. For casual use of your Fiat, either will work. If you are hard on your brakes, race your car, or descend down steep mountain grades, I'd use DOT 4.

DOT 5 is silicone-based and is not compatible with the rubber seals in your braking system, which is why you shouldn't use it.

-Bryan

[DieselSpider]

Some of the old rubber formulations don't last very long when a modern DOT4 brake fluid is used. Had the master cylinder fail and all hoses fail on mine when I first bought it and found the worksheet from the previous owner who had a few month prior replaced those items using IAP for the parts and it showed that the tire store he went to flushed out the DOT3 he put in with DOT4 and a phone call to him revealed that was when all his brake problems started. A chat with a bake component rebuilder who was at the local parts store when I went in confirmed that some of the older formulations of brake parts especially if they were old stock that had been sitting around may not react well to DOT4 so his recommendation was to stick with DOT3 and not chance having a reaction until I was 100% certain that all the components had been upgraded to be fully compatible with DOT4. I thoroughly flushed out the system with DOT3 and after replacing the failed components and have not had a problem since.

[18Fiatsandcounting]

Some of the old rubber formulations don't last very long when a modern DOT4 brake fluid is used.

Interesting, and I have not heard this. I have heard about the DOT 5 issues as noted above, but I've always understood DOT 3 and DOT 4 to be fully compatible, but with DOT 4 having a higher boiling point for brake systems that operate at higher temperatures.

Maybe I've been wrong all these years? Wouldn't be the first time!

-Bryan

[SteinOnkel]

Use DOT 4. Sold everywhere. It may even say DOT 3/4. DOT 5 will cause you problems; synthetic will cause you problems.

My '79 owner's manual specifies Dot 3.
Would there be a reason to vary from this and use Dot 4 instead?
Will using Dot 4 cause any problems?

Your manual is superceded. Yes, the advantages of DOT4 over 3 are plentiful. Higher wet and dry boiling points for example. No, DOT4 is compatible with your system.

I run Motul RBF660 in all my cars. That may be overkill for your application, but you should not go cheap on brake fluid. A good middle ground for you might be RBF600.

Whichever fluid you pick, swap every two years.

[SteinOnkel]

Some of the old rubber formulations don't last very long when a modern DOT4 brake fluid is used.

but with DOT 4 having a higher boiling point for brake systems that operate at higher temperatures.

That's every brake system if you operate it properly

DOT 4 is backwards compatible.

[DieselSpider]

Some of the old rubber formulations don't last very long when a modern DOT4 brake fluid is used.

Interesting, and I have not heard this. I have heard about the DOT 5 issues as noted above, but I've always understood DOT 3 and DOT 4 to be fully compatible, but with DOT 4 having a higher boiling point for brake systems that operate at higher temperatures.

Maybe I've been wrong all these years? Wouldn't be the first time!

-Bryan

I also thought it was fully compatible however apparently not quite 100%.

It could be that the tire shop used a modified DOT4+ or even just said they used DOT4 regardless of what was still in their flush and fill machine from the last brake flush.

Parts store manager verified that they had also been seeing failures when some of the newer DOT4 fluids are used in the older cars with OEM rubber formulations still in the system and New Old Stock parts appeared to be common theme in those instances so they recommended using whatever is stamped on the fill cap for the brake system to play it safe.

[18Fiatsandcounting]

Hmmm.... So maybe all DOT 4 fluids are not created equal? Could it be brand-dependent, in that some brands meet the DOT 4 spec but aren't as "good"?

-Bryan