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The final step is to bleed the brake system. We start by making sure our brake reservoir is completely full before we start the bleeding process. We used StopTech’s STR-600 High Performance Street Brake Fluid. StopTech also offers an STR-660 Ultra Performance Race fluid which has a higher dry boiling point, but we chose to go with the StopTech street fluid. Race fluids with higher boiling points tend to absorb moisture at a faster rate, so we chose to go with the performance street fluid to allow for longer intervals between fluid changes. In a race car where ultimate performance is desired and fluid change intervals are a non issue, the STR-660 race fluid would’ve been our choice. The technical white paper on brake fluid from StopTech is a good read if you’d like more info on the subject.
If you read the first part of our M5 project when we refreshed our stock brakes, you will remember reading about using a special BMW scan tool to activate the ABS system to properly bleed the system. We did not have one on hand at the MotoIQ Garage, but using our vacuum bleeder ensured we thoroughly bled our brake system without introducing any air bubbles. Once the calipers were full of fluid we finished the bleeding process the old fashioned way by pumping the brakes and opening the caliper bleed screws one corner at a time. We achieved good results with this method, but it is always best to have the BMW scan tool available to ensure zero air bubbles are in the system. Before we do our on road evaluation of our new braking system we will be making a pit stop to see the BMW Specialists at Pure Performance to give our brake fluid a proper final bleed.
Now it’s time to take a look at some real life comparison data. The chart above compares the sizes and weights of the stock brake components versus the new StopTech parts. The caliper comparison weights were taken with complete and loaded calipers. So the calipers had the brake pads installed and the weights also include the brake lines. We saved a significant amount of weight in the front corners of our M5 with 12 pounds of savings on each corner. In the rear we gained a total of 6 pounds on each corner between the heavier rotors and calipers, but keep in mind that we now have a much larger rotor and a 4-piston caliper in the rear of our M5 now.
Unfortunately our stock wheels will not fit over our huge front brakes, so we will need to upgrade our wheels before we can give our new brakes a thorough evaluation. Will we be able to negate the weight increase in the rear of our M5 with our new wheel/tire choice? You’ll have to stay tuned.
Our Project E39 M5 now has a set of world-class brakes that are more in line with its performance capabilities. We now have solid mounted multi-piston calipers on all four corners, along with better ventilated and light weight two-piece rotors. No doubt our performance sedan’s propensity to over heat the brakes has greatly diminished and we’re excited to feel the initial bite, modulation and feedback of our new StopTech Trophy Kit.
In the next installment of Project E39 M5 we will be installing a set of super lightweight forged Advan wheels wrapped in Nitto Invo tires. Then we will be able to get the car on the ground and bring you some proper impressions on how everything works. We are sure we will not be disappointed!
Sources
StopTech
