At my last autocross, I noticed that my braking seemed to be more black and white than shades of grey. Braking for a corner is difficult to judge and the soft pedal means I have to travel farther to stop as hard I want. I’ll admit that I haven’t paid much attention to my brakes in the last five years other than replacing the rear calipers with re-mans. Excessive brake dust and pad wear on the right rear prompted the swap, but I ignored the service manual and only bled the new rear calipers. Now I’m paying the price. Approaching a tight turn, I have to stab into the brakes in order to get any response. The rapid actuation removes any ability I have to modulate the input into a smooth action, and I end up running straight into the ABS. My hypothesis is that a firmer pedal will allow me to actuate the brakes more precisely and thus effectively. This will result in more on-throttle time, because I will be more confident in how hard I can brake approaching a corner.
In the spirit of this low-buck autocross campaign, I will start with the most simple and cheap solution: bleed the brakes. I have gone well past the recommended service life for the fluid in the system, and it’s not entirely unlikely that there is some gas trapped somewhere. In the next post, I will detail the process and results of bleeding the brakes per the service manual including cycling the ABS sequence control with the diagnosis connector. Furthermore, I will research the best available “parts store” brake fluid based on wet and dry temperature vs. cost, and will install temperature stickers to get some real numbers for caliper temperatures during an autocross. My next scheduled autocross is July 9th, so the Carolina summer heat will make for a great opportunity take brake temperatures in the worst conditions. Once I’ve got a clear picture of what I can do with my stock brakes, then I will dig into component upgrades.
Let’s start with some research. All of the most elite brake fluids are available to any consumer via the internet, but the exorbitant cost of some of the fluids on the market will make one consider, “How much should I really be spending?” For some perspective, NAPA-brand DOT 4 brake fluid can cost as little as $7.13/Liter, whereas Castrol React SRF Racing brake fluid can cost as much as $70/L before shipping! Higher quality and higher boiling temperature fluids will maintain their properties longer and in hotter conditions, but a balance must be struck between the fluid performance that your motorsport activity requires and the cost that your budget will allow. An important metric to remember when analyzing your brake fluid choices is the wet and dry boiling temperatures. The dry boiling temperature is for fresh, virgin brake fluid, which is most important if you’re replacing your fluid after each race. The wet boiling point is the boiling temperature when the fluid is saturated with ambient moisture (3.7% absorption per DOT specification). Brake fluid is hygroscopic and will absorb moisture over time. This absorption reduces the boiling point because the fluid is now part water and part brake fluid. The wet performance of the fluid is what makes the difference between the cheap stuff and the liquid gold. You can learn more about brake fluid in this great white paper from Stoptech. Because I’m going to flush the entire system simply to firm up the pedal and set a baseline, I will use a reasonable commercial product to start. Then I will attach temperature indicating stickers to the calipers in order to determine the peak temperature my calipers see during an autocross event. I will use this information to select a brake fluid that is appropriate for my current brake package and autocross level. Of course, the appropriate brake fluid will change as the braking system performance increases by component upgrade.
Here’s what I was able to find at your local auto parts store. This is not an exhaustive list, but it does provide some direction for choosing an off-the-shelf brake fluid with confidence. The Pentosin DOT4 has the highest boiling points for the lowest price above $10/L. Despite having an unpublished wet boiling point, the NAPA brake fluid is the best value by price and boiling point. Plus, since it is sold by the gallon there is plenty for flushing the system completely multiple times, if necessary or desired.
Neighborhood Store Brake Fluids:
Prices shown are found in the Charlotte, NC area
Pentosin DOT 4 (Highest Performance)
P/N: BF-DOT4-1L @ O’Reilly
Dry Boiling: 509°F
Wet Boiling: 329°F
NAPA Brake Fluid (Best Value)
P/N: NBF 40101 @ Napa Auto Parts
Price/QTY: $26.99/G. (or $7.13/L)
Dry Boiling: 480°F via MSDS
Wet Boiling: Not Available
Prestone DOT 4
P/N: AS800Y @ AutoZone
Price/QTY: $4.99/12oz. (or ~$14.06/L)
Dry Boiling: 500°F
Wet Boiling: 311°F
BrakeBest Select DOT 4
P/N: 80034 @ O’Reilly
Price/QTY: $4.89/12oz (or~$13.77/L)
Dry Boiling: 475°F
Wet Boiling: 320°F