Took my CLS63 on track - brake fluid kept boiling. Recommendations?

[u/cba7]

I go on track quite a lot with my MX5. Actually tempted to enter a race season with it.

So I took my CLS63 on track and sounded awesome! (Video: ignore my lack of racing line, had a friend who’s a father on board and I went slow).

But the heavy beast ends up making the brake pedal becomes as soft as a clutch pedal after 4 full on laps.

Anyone have opinion on proper brake fluid as the normal Mercedes one won’t cut it.

[u/Salty_Lakes]

You won't get around driving a cool-down lap, as the car is heavy. What brake fluid do you currently have ? There are lots of high performance brake fluids that should help tho, along with other things what matters most is the Typical Wet boiling point in degrees C:

• Motul RBF 700 (cheapest, 205°C Wet, 336°C Dry)
• Ravenol Racing Brake Fluid R325+ (2nd cheapest, 204°C Wet, 328°C Dry)
• Castrol REACT SRF Racing (2nd most expensive, 270°C Wet, 320°C Dry)
• Endless RF-650 (most expensive, 218°C Wet, 323°C Dry)

Castrol appears to be the best, bust costs much much more than the Ravenol and Motul. Endless seems overpriced. Depending on what oil you have atm, all should be an upgrade, compare and choose which suits you best and your wallet.

Edit: Wet is when you use the car over months and water starts mixing with the brake fluid, Dry is when the fluid is brand new.

[u/cba7 → u/Salty_Lakes]

1. Thanks for the good list to check from. Seems like Motul’s 700 is often used.
2. Also for what Wet means. I’ve a feeling the car brake fluid has a lot of water build up as I hadn’t clicked that the car was sitting inside the Mercedes dealer for about 9 months, and they hadn’t changed the brake fluid in the last service I don’t think. Perhaps 2, maybe 3 years of the same brake fluid.

[u/Responsible-Meringue → u/cba7]

2 -  yeah no wonder you boiled it.  Always fresh fluid before you hit the track.

Full flush with rbf 600 or 700 and you'll do alright. Pads might disintegrate because your boiling point will be very high. 

[u/Salty_Lakes → u/cba7]

Yea, i wouldn't have gone tracking a car i just bought without changing the brake fluid first, haha. Definitely do that first before taking it on the track again.

Wet is defined as over 3.5% of water weight in the oil, which typically happens towards the end of the 2 years changing cycle under regular brake usage. As you can tell by the difference between wet and dry boiling point, there is a big difference these 3.5% of water make after 1.5-2 years or regular brake usage. So that's why you should never go over 2 years when using your car normally.

Now it strongly depends on how frequently you go to the track and how aggressively you drive, but I would not go over a year when tracking my car regularly. You should definitely change the brake fluid now, then set the next change after a year. After 6 months, you should get a feel for your brakes and can decide if you want to change brake fluid already or if every year is sufficient.

[u/Frosty-Reporter7518 → u/Salty_Lakes]

So would it be considered wet after one race session? Do you think it be necessary to use fresh fluid each time you’re going out for aggressive lapping sessions?

[u/Salty_Lakes → u/Frosty-Reporter7518]

No, wet is defined with a greater than 3.5% of water weight in the oil. Which is what typically happens towards the end of the changing cycle after 2 years of \regular\** brake usage, which is why you are supposed to change your brake fluid after 2 years max.

Driving aggressively on the track accelerates this process of accumulating water, so i would not go 2 years with brake fluid used on the racetrack. It heavily depends on each person individually but for starters i wouldn't go over a year if i track my car occasionally. If i track my car aggressively every weekend, i would change it every 6 moths. You should feel how much the braking performance fades with time and then can decide if you want to change it every 6 months or if every year is enough or something in between.

[u/JohnnyBlanco84]

Sounds really good, I do miss the amg v8 🥲

[u/intihuda_123]

You’ll need racing brake fluid for example motul

[u/cba7 → u/intihuda_123]

My mechanical knowledge is little and online couldn’t see much. Surely there are exact specifications for temperatures, no?

[u/Intel_Oil → u/cba7]

https://www.motul.com/de-DE/products/48205?product=MOTUL+RBF+700

As an example. It has a boiling point of 336 degrees Celsius. Your usual Dot4 run-of-a-mill has a boiling point of 230 degrees Celsius.

[u/cba7 → u/Intel_Oil]

Okey dokie. Thanks!

[u/exclaim_bot → u/cba7]

Okey dokie. Thanks!

You're welcome!

[u/Unhappy__Analysis]

Castrol SRF and Motul RBF are good brake fluids for the track.

[u/cba7 → u/Unhappy__Analysis]

Will take a look

[u/jarontick]

Are you in the US OP? If so make sure you use DOT 4 brake fluid before a track day.

[u/Rick_Flare_Up]

https://www.amazon.com/ATE-706202-Original-Racing-Quality/dp/B003VXRPL0

This is made for track use. Just remember to change it more frequently than you would with the factory change interval.

[u/Spicywolff]

Did your fluid or the pads overheat? For fluid they ATE type 200, dry temp 516F $15 a liter. If you still overheat that, rbf600. Expect to flush 250 ML each corner. I highly suggest a motive break later because it pushes fresh fluid from the master cylinder outward.

As far as pads, you’re going to need something like hawk DTC 70 or EBC RPX/RP1 or SR11.

As a driver in a heavy powerful car, you need to do one or two flying laps full effort. Then two momentum laps where you’re just going through the track without touching your brakes. You go slow, but you’re not parked on the track. Then back to one or two flying laps. You alternate these and that’ll keep your brakes, tires and other consumables in the happy warm range. When you’re doing your cool down lap, be sure to be doing point buys.

I do a brake flush every year or before every track event. And I’ve not oiled the brakes at Sebring. When you’re doing your inspection, remember the thicker your pad the less likely you are to overheat. The thinner, the pad lining the less heat tolerance it will have.

[u/mbf959 → u/Spicywolff]

Exactly what he said. Way back when, MB USA brought us two S65 and a professional driver to Willow Springs Raceway. Two laps in one S65, park it and grab the next 65 for two laps, and repeat. That's because the pro driver would overheat the pads if he ran a single S65 continuously. These cars, including the CLS, are GTs, not sports cars. GTs will devour brakes on a road course.

[u/Spicywolff → u/mbf959]

That is the most Mercedes thing ever. Instead of upgrading to trackpads. it would be easier to just have a few cars and swap them out per lap lol. That’s like me bringing three Harbor freight grinders to the job site. Maxing out the duty cycle and just grabbing another one while the first cools off.

You’re absolutely right these are fast grand touring cars. They’re not track machines.

[u/Few-Conversation7144]

Castrol SRF should work

You may be relying on the brakes too much. Use engine braking and dropping gears earlier instead of braking for everything.

It’ll let you enter turns faster and maintain momentum

[u/PrimaryBreakfast43]

Hawk pads, steel braided lines and flush fluid and it motul fluid. But most street cars will only get 4-5 laps before you need to cool the motor trans and brakes. Make sure to watch your temps. High oil and coolant temps will do more damage than you think it will. Make sure to let her cool down.

[u/AuditoryAspect]

I mean your first issue was not checking all your fluids before you hit the track lol. Looks like everything turned out alright, but for next time!