dot 5 silicone brake fluid

[patriot68]

can i use dot 5 brake fluid in my 68 camaro for brakes and clutch?. my brake and clutch systems are completely new..calipers/lines/master/slave....i would hate to ruin my paint if regular brake fluid spilled on it. thanks
scott

[orange88]

dont quote me on this but i think you need diffent seals in everything

[kennyd]

i run dot 5 in everything i build new . and never had any problem

[patriot68]

thanks..

[XcYZ]

How much heat can DOT5 take? I've heard all kinds of stuff, but it's all over the board.

[Blown353]

Originally Posted by XcYZ

How much heat can DOT5 take? I've heard all kinds of stuff, but it's all over the board.

DOT5 (silicone-based) fluid by itself is OK in terms of the boiling point... the bad part is it's hydrophobic (i.e. repels water) and because of the density difference all the water collects in the lowest parts of the system (the calipers) therefore you have all the water concentrated at the hottest point in the braking system. That's bad. Might as well consider your boiling point to be 212F or thereabouts depending on altitude because once the calipers heat up it will flash the water that is puddled in them.

It's not a matter of if water will get into your brake system but how much water is in your brake system and how much more is added every day.

DOT 5 likes to aereate and become "spongy", it's tough to bleed, not to mention the water issue is the nail in the coffin. It's great for show cars that only need their brakes getting on and off the trailer but that's where the goodness ends. The only redeeming quality to the stuff is that it does not eat paint and that does not at all outweigh all the other major issues with the stuff which are ALL safety related.

Don't confuse it with DOT 5.1 though, that is a totally different animal.

Use good DOT 3/4 or newer 5.1 fluid (I like ATE Typ 200 / SuperBlue) and change it occasionally and things will be OK.

Good reading here: http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

[XcYZ]

Excellent info, thanks Troy.

[kennyd]

i have used dot 5 for years and never had provlem . i dont deny what he is saying , but i drive some of my cars hard real hard , i have a 57 with a 502 6speed ,bags, brakes, and i drive the living **** out of this car . i have not experenced any fade . and my master cyl is still painted .
like he is saying for a driver i say yes , for a road racer car NO .

[Blown353]

Fade is not the issue with DOT5-- it's boiling off the moisture that gets trapped in the lowest point in the system. If there is an appreciable amount of moisture in the system (it will take time) and you get the brakes hot, it will boil and you won't have ANY brakes. With a standard Dot 3/4/5.1 brake fluid the moisture is evenly absorbed resulting in a gradual lowering of the boiling point as the overall percentage of moisture suspended in the fluid increases. With DOT 5 you get big pockets of water at the low spots which boil around 212F which is much lower than even the moisture saturated boiling point of a good 3/4/5.1 fluid.

I've boiled brake fluid several times in different cars and the worst cases involved DOT5 in friend's street rods (who put the fluid in because they didn't want to damage their super-nice painted engine compartments.) Also, with DOT5 my experience is the pedal will get "spongier" if you drive into higher altitude than where the system was filled because the difference in atmospheric pressure causes the bubbles in the fluid to grow. Driving from here (15' above sea level) up to Reno (about 4400') resulted in a very soggy low pedal in a friend's 32 Roadster... which was somewhat squishy to start with because of the nature of DOT5.

I've seen the inside of calipers of DOT5 systems after prolonged fills without flushing; they were rusty in the bottom from pooled moisture which caused the seals to leak and thus prompted the replacement.

One point of note: I don't believe any OEM out there uses DOT5 as a factory-fill in their brake systems. That's a very important piece of data IMO. In fact, the only non-DOT 3/4/5.1 factory fills I have ever seen in a car is some Bentleys which use mineral oil (which is also shared with the load levelling suspension) but that is a very oddball atypical setup.

If you're having good luck with DOT5, cool. I for one have had too many negative experiences with it and after some research and a decent understanding of the moisture interaction properties of DOT5 I will never use it in any of my vehicles from a safety standpoint. Keeping the paint pretty under the hood is much less of a concern to me than having my brakes work when I need them. I'm a big propnent of using a good 3/4/5.1 fluid and doing flushes at least yearly or prior to any track event where you'll be using the brakes very hard for sustained periods of time.

[Derek69SS]

What is DOT 5.1? I'm not familiar with that.

I just recently flushed out the DOT 5 from my car, and replaced it with 3 since I do intend to track the car.