I do some occasional track work and my first autox this weekend. Is there really any benefit to using DOT 4 vs DOT 3?

 

Yes. The dry and wet boiling points are increased quite a bit.

I've boiled fluid before and it's NOT fun.

Get yourself a can of ATE Super Blue and ATE TYP 200 fluid. They are both the same fluid specification but one is blue and the other is amber in color which makes flushing the system easier.

And yes, flush the entire system. Any fluid that you don't use needs to be thrown out because it will absorb moisture while it's in the can after being opened.

Now, for auto-x you probably don't need to, but I flush my entire system with brand new fluid before every open track event.

It only takes 20-30 days for the fluid in the lines to absorb all the moisture and become "wet" with it's reduced boiling point.

 

autocross no, track yes. Dot 3 will not hold up to repeated laps. Personally, I think it's a waste of time to flush the entire system for every track event. Yes, the fluid will eventually absorb some moisture but this does not happen in a sealed system within a few weeks. I go for a whole season without any problems but it's up to you. If it makes you feel better to change it every 2 weeks, do it.

 

I can guarentee that if you ever suffer a major brake fade event (and survive) that you will never go to the track (subsequently) without fresh fluid (and higher temperature pads). Brake fluid is 200 times less expensive that body work--ask me how I know.

If you are flusing the system for the first time, then there will be residual water in the rubberized parts of the brake system that will accelerate the 'wettening' of this batch of brake fluid. If you change your brake fluid again within 3 months, or so, then this residual water is at minimal levels.

If only takes an hour from the water vapor that ingresses the fluid at the brake caliper (seals) to reach the master cyclinder. The black crap that comes out with a bleed is the fluid that you have (heat) stressed and is no longer operating as a Dot 4 or Dot 5.1 fluid. The black crap is not from the water vapor, but a breakdown of the glycols themselves.

 

When purchasing fluid, don't simply go by DOT4. The minimum requirements for being classified as DOT4 aren't very high, it something like 315 degree wet boiling point. The wet BP is the important one, not dry. The ATE that JLMounce suggested has a wet BP somewhere above 390deg. I use that and have been happy with it. Other good brands heave similar boiling points or higher. They cost about twice as much (or more) as the cheap ones that barely make the DOT4 spec, and are worth every penny.

 

Would this be good for clutch fluid as well????

 

GM specs DOT 3 for the brakes and DOT 4 for the clutch.

 

Yup. Same deal, they just have different minimum requirements as calemasters pointed out.

 

I did experience that feeling about 15 years ago but there was always plenty of warning that it was coming. I just slowed down and went back in the pits and fixed it. WHat I need is a warning for when my race pads are gone.

 

so spell it all out simple for me guys......

Your recommendation for brake fluid?
Your recommendation for brake pads?

Driving style/habit would be.....

mtn runs multiple times a year
5-7 autocross events a year
2-3 track days
spirited street driver


Thanks.

 

Calemasters,
Does the 06 z51 6spd come with Dot3 or Dot4 for brakes/ clutch and is the fluids Synthetic? If you only change the fluids in the reservoirs without uncovering the little hole at the bottom, drive the car and do this a few times, will it make a difference IYHO.
David

 

The 2005 - 2007 Corvettes come from the factory with:

DOT 3 Brake Fluid (non synthetic)
Dot 4 Clutch Fluid (manual transmission) (non synthetic)

 

It doesn't really matter what they came with. DOT 4 synthetic can be mixed with DOT 3 or DOT 4 non synthetic or synthetic and will not harm the brake or clutch system. I use Valvoline DOT 4 synthetic across the board. Lots of experience with clutch pedal to the floor syndrome on the old C5.

 

OK

"How Do Brakes Work?
An automotive hydraulic braking system consists of a master cylinder, four wheel cylinders, metal tubing and flexible rubber hoses. This hydraulic system attaches to frictional components that are comprised of brake shoes and drums or brake pads and discs. The brake fluid is contained within the system assembly. When pressure is applied to the service foot brake, the master cylinder exerts a force of fluid. This force actuates the wheel cylinders to push the brake shoes against the brake drums or the pads against the discs, resulting in the braking action. Application of the brakes turns the energy of the vehicle into friction heat at the brakes.(3) This brings the brake temperatures to high levels. If the brake fluid has been contaminated by excessive usage of high heat the boiling point can greatly be reduced in a short period of time. A vehicle that has been in service for 18 months with 25,000 miles of service, could have the working temperature of the brake fluid reduced by as much as 25%. If the fluid's working temperature were reduced by 25%, the moisture content would be equivalent to 3%.

Conventional DOT3 brake fluids will absorb and average of 2% or more of water in the first year of usage. In that period, the boiling point can drop from 401 degrees to 250 degrees, a reduction of over 150 Fahrenheit degrees.(6) Brake fluid designated a DOT4 possesses an important characteristic, having low moisture activity or improved ability to resist boiling point drop. This boiling point drop becomes essential in assuring safe brake operation.

The boiling point of new DOT 3 brake fluid is 401 degrees Fahrenheit. Contaminates such as moisture, dirt and corrosion greatly reduce the boiling point of brake fluid. High temperatures encountered in ABS disc brake applications require hydraulic fluid specifically formulated to withstand the higher temperatures than normally experienced in drum type brakes.( DOT 3 was desinged for DRUM brakes not Disk Brakes) Modern hydraulic brake fluids are designed for high boiling points because of the extended temperature ranges prevalent in disc brake service. Small amounts of contamination such as foreign material, vapor and water greatly decrease the boiling point. When the service temperature exceeds the reduced boiling point, contaminated brake fluid will vaporize and prevent positive braking on the subsequent application. Besides materially reducing the boiling point, moisture promotes rust in steel brake lines, sludge in cylinders and corrosion inside wheel cylinders and calipers"

As a result of the above, brake fluid should be choosen on the WET not DRY boiling points

BRAKE FLUID COMPARISON CHART

Brand Wet Boiling Point Dry Boiling Point
Castrol SRF 518°F 590°F
Motul RBF600 420°F 593°F
Wilwood EXP 600 417°F 626°F
AP-600 410°F 572°F
ATE-Super Blue 392°F 536°F

Valvoline 333°F 513°F
Castrol LMA 311°F 446°F
Ford HD 290°F 550°F
Wilwood 570 284°F 570°F
PFC-Z rated 284°F 550°F
AP-550 284°F 550°F


For any DEs or Auto-Xs or heavy spiritied track use or driving, DOT 4 with a WET boiling point as close to if not above 400* should be choosen.

Brake fluid must be flushed, not bleed, but flushed before each Track / Auto-X weekend. There may also be cause to bleed each caliper several times during the event as well.

Tom

 

Spells it out for me, thanks Tom.