Ohmess

I just bought an E350 4matic for my wife and the brake fluid has never been changed. Is there anything unusual about the process of changing the brake fluid on this vehicle? I have done this multiple times and know the basics; my specific concern relates to any possible need to interact with the computers in the car.

konigstiger

WIS instructions...

Mud

When I did this I used a Mityvac at each caliper, started with RR first then LR, RF, LF. Suctioned out fluid while keeping an eye on the reservoir. Refilled with the recommended Pentosin fluid as I went until everything was a nice clear fluid. One quart was more than enough.

mercy-me

I just did mine which had never been done either. No computer involvement whatsoever.( No SBC on our W212's)

I have a homemade Mityvac like setup that I use. Suction out as much fluid as possible from reservoir then re-fill with Dot 4 Plus fluid. Screw on adapter cap to reservoir then pressurize to 1 Bar (15psi). Start with RR and open bleeder screw. Pressure in reservoir will push fluid out through line. Use a hose over bleeder to direct fluid into a clear vessel and bleed until color is same as new stuff in reservoir. Stop and re-fill reservoir often to not allow it to run dry. Continue around car LR, RF ad LF and done.
I used about 3/4 Liter Pentosin Dot 4 Plus. Also, no need to remove the wheels. I had my car up on jack stands to do an oil change and differential fluid change so very easy access. It is amazing to me that more people don't do their brake fluid more often. It's in the maintenance book schedule.

Welcome to the forum and Good Luck,

Bob

Ohmess

Wow! Prompt replies and right on point. This is outstanding. Thank you all.

Sunnyslope48

X2 .

Alandf

Considering that the reservoir itself holds 85% of the fluid in the system why wouldn't it be sufficient to merely drain and fill the reservoir? Any slight contamination would be distributed in the new fluid.

All replies appreciated, even if I am totally wrong in my logic.

Sunnyslope48

If that 85% number were accurate, I would agree with you. However when you consider the 4 calipers plus lines plus ABS, I doubt it would be more that 40%-50%. But your point is well taken. If a person were to change just the fluid in their master cylinder at every oil change, that would go a long way in prolonging the efficiency of the brake fluid in the system. I also own a Chevy diesel truck and that's exactly what I do with that, change MC brake fluid at every oil change. Brake fluid is pretty cheap and doesn't take much, so, why not?







%

Mud

The fluid that sits inside each caliper sees a lot of heat cycles and the flex hoses and caliper seals contribute small bits of debris over time. That fluid doesn't really go anywhere - it just sits and degrades slowly over time. The MC is a reservoir - you don't have a return system going back to it. There's nothing that circulates brake fluid. So changing the reservoir fluid is not a bad thing but doesn't really do much for fluid in brake lines and at wheels.
That's also why you should open a bleeder at each caliper when you compress the piston for new pads. This lets old dirtier fluid out of the system rather than push it back into the ABS/brake lines. Better yet is to flush the system with any brake work.
I'll echo that brake fluid is cheap - a liter of Pentosin was $8 at Rockauto as I recall.
If you use a Mityvac or pressure bleeder the flush process is easy and quick, more effort to r and r the wheels than to do the actual bleeding. For me I flush the fluid every 1-2 years depending on miles driven and anytime I work on the brakes.