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Hello Forum,
On my 2017 C43, what is the proper way to fully flush/change the brake fluid. I have a pressure bleeder I can hook up to the fluid reservoir, and I also have a MityVac I could use to pull the fluid at each wheel. But, my concern is the ABS and whatever else controls braking on a "modern" car. At the dealership, does a mechanic hook up a computer that forces the ABS to actuate and move fluid through that system? Is it ABS that brakes one rear wheel to pull you back into your lane when you drift, or is that a different system? Thanks for the help!
I did my G550's brake fluid last year using a Motive pressurized reservoir method, which is the technique described in the MB WIS. The procedure said nothing about the ABS, and my understanding is that the amount of fluid that resides in the ABS components is negligible, and only needs attention if an ABS component has been replaced. Like an oil change, you can't extract every last ml, so you accept dilluting 5% of old stuff with 95% fresh stuff and call it good enough.
Hello Forum,
On my 2017 C43, what is the proper way to fully flush/change the brake fluid. I have a pressure bleeder I can hook up to the fluid reservoir, and I also have a MityVac I could use to pull the fluid at each wheel. But, my concern is the ABS and whatever else controls braking on a "modern" car. At the dealership, does a mechanic hook up a computer that forces the ABS to actuate and move fluid through that system? Is it ABS that brakes one rear wheel to pull you back into your lane when you drift, or is that a different system? Thanks for the help!
Originally Posted by streborx
I did my G550's brake fluid last year using a Motive pressurized reservoir method, which is the technique described in the MB WIS. The procedure said nothing about the ABS, and my understanding is that the amount of fluid that resides in the ABS components is negligible, and only needs attention if an ABS component has been replaced. Like an oil change, you can't extract every last ml, so you accept dilluting 5% of old stuff with 95% fresh stuff and call it good enough.
OK. I'm getting ready for another HPDE weekend at Mid-Ohio. Wanted to get the Motul 660 in there for the year. I'd have to look at the papers again, but I think the dealership replaced my brake fluid at the last service.
OK. I'm getting ready for another HPDE weekend at Mid-Ohio. Wanted to get the Motul 660 in there for the year. I'd have to look at the papers again, but I think the dealership replaced my brake fluid at the last service.
MB recommends every B service, do you go with that schedule? If so then you are good.
@streborx Does the WIS specify sequence of wheels? I assume:
1. Passenger rear
2. Driver rear
3. Passenger front
4. Driver front
The sequence depends on the location of your brake fluid reservoir, and starts with the caliper furthest away and works toward the closest. The sequence you list is correct for the reservoir mounted on the driver's side (which I think is where it is on most cars).
Question: when the new and old fluid look the same, how do you know when you have the whole line purged? How much fluid should be in the longest line?
Water content alone does nothing to discolor brake fluid. If your brake fluid is dark, it's a consequence of oxidation -- not good. My brake system capacty is about 1 liter. I bought 2 liters of new fluid and removed 1/2 liter from each rear calipers, and about 1/3 liter from each front caliper. There was no discernable color difference -- I just assumed bleeding out these quantities was sufficient.
To amuse myself, I tested the extracted fluid with a $25 brake fluid conductivity tester and with an oxidation test strip. Neither test revealed any evidence of water contamination in either the extracted fluid or the new fluid, but I don't have any confidence in the reliability of these test methods. But I'm also skeptical that 30ml of water could enter a sealed hydraulic system in 24 months.
I'll do that going forward, unless someone has a more definitive, documented answer.
Where does this 30ml of water comment come from?
That's the question I always ask, and the brake gurus always remind me that brake fluid is hygroscopic (absorbs water), and therefore water contamination happens. But how does water enter a sealed hydraulic system? Some systems are vented, but even so, a cubic meter of air can hold about 17 ml of water at 20C (100% humidity), so it would take about 2 cubic meters of water saturated air circulating through the small space at the top of a brake fluid reservoir with complete absorption of the water to contaminate 1 liter of brake fluid with 30ml of water and achieve 3%. Others insist water enters via osmosis through hoses and seals at atmospheric pressure when the system is designed to withstand 2000 psi fluid pressure. I might purchase a boiling point brake fluid tester and take some measurements. As I said, the inexpensive conductivity testers are unreliable.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by streborx
That's the question I always ask, and the brake gurus always remind me that brake fluid is hygroscopic (absorbs water), and therefore water contamination happens. But how does water enter a sealed hydraulic system? Some systems are vented, but even so, a cubic meter of air can hold about 17 ml of water at 20C (100% humidity), so it would take about 2 cubic meters of water saturated air circulating through the small space at the top of a brake fluid reservoir with complete absorption of the water to contaminate 1 liter of brake fluid with 30ml of water and achieve 3%. Others insist water enters via osmosis through hoses and seals at atmospheric pressure when the system is designed to withstand 2000 psi fluid pressure. I might purchase a boiling point brake fluid tester and take some measurements. As I said, the inexpensive conductivity testers are unreliable.
Not really sure about how air enters the brake system, but if a line goes out because of corrosion or rust (like it did on my 2000 Ford F150 with 225,000 miles), it ain't fun. Plus, I look for every opportunity to spend quality time with my car.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by GermanCarShow
@streborx Does the WIS specify sequence of wheels? I assume:
1. Passenger rear
2. Driver rear
3. Passenger front
4. Driver front
It's best to always check the service manual for the correct bleeding sequence and any other processes (for any vehicle). Probably 98% of the time, the sequence is what you listed. However, I know my 2004 SL500 with SBC had a completely different method requiring a bi-directional scan tool (such as XENTRY, Autel, etc.) to activate the SBC during the process. It would automatically flush the brake line of each wheel, but the sequence was different. (There was also a warning that SBC must be deactivated when doing any kind of brake work as a safety precaution.) Recently, I replaced the rear section of a brake line on my 2004 Audi TT and it too has a specific process that requires activation of the ABScontroller using VAG-COM/VCDS. So, it's always best to check in the WIS first.
Not really sure about how air enters the brake system, but if a line goes out because of corrosion or rust (like it did on my 2000 Ford F150 with 225,000 miles), it ain't fun. Plus, I look for every opportunity to spend quality time with my car.
Seems more likely your Ford was a victim of road salt than from corrosion due to a bit of water in the brake fluid (?).
25 years and 225K miles on a Ford -- can't complain! When I lived in PA, there were 5 year old cars dropping their exhaust systems on the highway due to total salt-induced rust out.
Hello Forum,
On my 2017 C43, what is the proper way to fully flush/change the brake fluid. I have a pressure bleeder I can hook up to the fluid reservoir, and I also have a MityVac I could use to pull the fluid at each wheel. But, my concern is the ABS and whatever else controls braking on a "modern" car. At the dealership, does a mechanic hook up a computer that forces the ABS to actuate and move fluid through that system? Is it ABS that brakes one rear wheel to pull you back into your lane when you drift, or is that a different system? Thanks for the help!
Power bleeder should be the way to go, FCP Euro has a good video on how to use them. If you're using the power bleeder there should be no need for the MityVac.
There's really no need to use a scan tool to run the "ABS module bleed" procedure unless you're had the lines off the car. That being said there IS a scan tool procedure for doing just that, but it's likely NOT needed as long as you keep the master cylinder full of fluid while you do the flush (hence the power bleeder).
Before deciding to use the Motive system that adds fluid to the reservoir under pressure, I did a bit of research on the reservoir method versus the pistol pump that pulls fluid from the caliper. The major concern with the pistol pump method is ensuring a tight seal around the bleed nipple so that air doesn't get sucked back in.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Be sure NOT to over-pressurize the power bleeder when using it. Different manufacturers have different tolerances, but if you set the pressure too high, there may be a valve that limits the bleeding function. Below are instructions for bleeding my 2004 Audi TT quattro. As you can see, the pressure of the bleeder must not exceed 1 bar. I will check WIS to see if there are similar warnings for Mercedes.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Here you are boys and girls. It appears Mercedes says to set the pressure of the power bleeder to 2 bar. The sequence is the traditional way starting with the brake furthest away from the master cylinder or brake reservoir. (At least on my 2014 C-Class.)
My Motive instructions state 15 psi (~ 1 bar) or whatever the manufacturer states. WIS for my G550 says 2 bars. I think I kept the Motive tank as close to 30 psi throughout.
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