Brake fluid type

[67SS]

I am installing a SSBC aluminum master cylinder on my '67 S/S. I've got 12" Wilwoods up front and stock '69 drums in the back. What brake fluid should I use DOT3 or DOT4? What is the difference?
Thanks
Mark

[Apogee]

Any DOT3/4/5.1 fluid should be good for your system and unless you track the car, you'd be hard pressed to tell the difference between them under normal street driving conditions. The higher the DOT number, the higher the dry/wet boiling point range. Avoid silicone DOT5 fluids and you should be fine.

Dry/Wet temp ranges are as follows:
DOT3 401/284 F
DOT4 446/311 F
DOT5 500/356 F
The temperatures given above are the minimum required temperatures that the fluid must meet in order to satisfy the DOT requirement along with a bunch of other parameters.

Tobin
KORE3

[67SS]

Thanks for the help. Any reason you wouldn't want to run DOT4 if the boiling point is higher then DOT 3?

[Apogee]

Nope, no reason really. DOT4 is typically a bit more expensive than DOT3, but well worth it IMHO. Plus, it's still cheap when compared to most of the 5.1 and race fluids that are available. The "wet" boiling point tends to be the more important of the two boiling points since your brake fluid starts absorbing moisture from the moment you open the container...and even before in most cases. A decent fluid that gets flushed/bleed regularly yields very good results with respect to performance and overall system longevity/maintenance.

Tobin
KORE3

[noobwrench]

Thanks for the help. Any reason you wouldn't want to run DOT4 if the boiling point is higher then DOT 3?

Most dot4's and dot5's are much more hygroscopic than a similar quality dot3.

The better quality fluids will be less likely to fail as quickly, im a HUGE fan of the Castrol SRF fluid, but id still change it every 6 months in a performace application.

[Apogee]

Most dot4's and dot5's are much more hygroscopic than a similar quality dot3.

The better quality fluids will be less likely to fail as quickly, im a HUGE fan of the Castrol SRF fluid, but id still change it every 6 months in a performace application.

You're right that most DOT4/5.1 fluids are more hygroscopic, that's why it's the "wet" boiling point that is the more important number when selecting a fluid for a street application. Castrol SRF is bit overkill for the street, and at $74.95/liter is doesn't easily fit into most people's budgets.

Tobin
KORE3

[noobwrench]

at $74.95/liter is doesn't easily fit into most people's budgets.

Tobin
KORE3

0.o I never knew what retail was on that, I get it alot cheaper than that.

[silver69camaro]

0.o I never knew what retail was on that, I get it alot cheaper than that.

Where? I've never seen it less than around $75.

[T-CHRGD]

For what it's worth, I run Valvoline DOT4 Synthetic