Yes, I know that brake fluid should be replaced periodically. For some reason, I have trouble keeping to a schedule on that and have ley my cars go far beyond that ISTS. A viable option, and one that I will do on my MB when I go through the brakes and replace some other compionents is silicone brake fluid. Silicone brake fluid is non-hydroscopic, so it doesn't need to be replaced. It also has a higher boiling point and as you might expect is more expensive.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I, humbly, think you are right. After finishing the job and taking it for a drive, I could swear that there is still some air in the calipers. The pedal travels more than it should and it is softer than it was before the calipers were replaced.

I had attached the Easibleed and used it as well, but, the flow rate is still fairly slow and no air was apparent. Might have to up the pressure or, return to the "two man" method.

You can open all 4 corners and let it gravity drain the system...just filling the reservoir when it is low does not help fight moisture in the lines. Let it gravity drain and then refill the master cylinder and then you can either bleed the lines with 2 people or by yourself you can gravity bleed the system....Jim

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James A. Harris

Brake fluid is cheap, I do mine every spring.

Now while were on the topic how many people out their have changed their soft brake lines? I did mine last spring and they were starting to crack; now since my car is an 87 their are a lot of cars on this forum that are older then mine. So if you have never changed those lines and have no record of it being done change them!! Their about $10 each don't cheap out, I think they should be replaced every 10 years or 100k miles.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

bad a severe brake grabbing problem on my 80 chevy truck. A friend told me he had the same experience and someone convinced him to change the hoses and problem went away. I was like "yeah sure" -the hoses seemed OK, but I was out of ideas so i finally changed them. Now I believe, I BELIEVE< I BELIEVE

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Hoses collapse internally. When you apply the brake, you can push a couple thousand psi through the lines, but the return pressure is not enough to push it back through. What you get is sticking brakes.

When the hoses fail internally the pressure you apply works it's way between the hose lining and the rubber outer. Now when you apply the brakes the pressure effectively collapses the inner hose preventing the fluid from reaching the calipers. You won't be able to see any sign of failure from the outside in many cases.

Silicone fluid is bad, bad news for daily drivers - I would not use it. It is not compatible with ABS systems, must be handled very carefully to avoid air bubbles, and the moisture which makes its way into the system will bead as droplets and collect at the low points of the system which then corrode. It also doesn't mix with regular fluid. It's typically used in track applications where the systems are regularly serviced and the high boiling point is important.

There's no need for anything fancy or tricky where brakes are concerned, just use any DOT 3 or 4 fluid and replace it every 12 to 24 months.

Kevin

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'85 300SD

I have heard different figures for brake system hydraulic operating pressure. Did you get this figure from a reliable source or is it an estimation?

I don't remember exactly what I read about silicone brake fluid but the gist was to use it only where recommended. I don't know what MB says about it.

This is an excellent thread that whunter recently posted a link to, I think it worth repeating.
Both are excellent threads but it was the 126 brake thread that I was thinking of.

This is the way I always bled motorcycle brakes, it is the only way I have had reliable performance from the Mityvac bleeder.

Danger!!!
Never use silicone = DOT5 fluid in any ABS system that does not call for it…

Silicone brake fluid can be bad in any system not made for it.

A friend changed his MGA to silicone, went to Europe for five years, returned home, dropped fuel and a new battery in the car, and drove off to visit a friend.
The seventh time on the brakes there was a hard kick from the brake pedal, then no brakes at 70 MPH in expressway traffic, coming up on a construction zone.
He hit the ditch and wrecked the car in trees.
The insurance investigator proved that while the silicone did not absorb any moisture, the system still accumulates moisture, under the wrong conditions = long storage no driving.
The system gets hot; moisture flashes to steam and explodes the weakest point in the system.
In his case the flex hoses burst.

This is a safety system.
You do not want to explain to a judge why you changed the specification of fluid for a safety system.

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ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

VERY, VERY true. Only use the type of brake fluid recomended by your manufacturer. And NEVER, EVER mix types.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

OK, 1. I know silicone is not recommended in ABS systems, I assumed that was commonly known and shouldn't have 2. Switching to silicone makes sense IMHO only if the whole system is being adressed at once, because the old brake fluid needs to be thoroughly flushed out of everything. I've done it twice and that was when EVERYTHING was replaced:new metal lines, new hoses, new or rebuilt wheel cylinders - probably not practical for most MB owners with the cost of parts today 3. Simply draining the system and refilling with silicone is NG, that's probably what the guy did with the MBA. If he left moisture in the system when he drained it, it was still there. He wouldn't have been safe if it was filled with DOT3 either. So I retract my recommendation of silicone fluid to everyone except those few who would remove all of the old fluid

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Twitch, it's just a generalization. It really depends on the brake system. 2000psi in a brake system is quite common. On some systems, it can be less and on some it can be much more.

There is a good article (with a test) on the complete brake system at http://www.abbysenior.com/mechanics/brakes.htm for those that want to know the inner workings and the "why" of the brake system.

Silicon fluid is bad for this reason.....then moisture that does manage to condense in the M/C will eventually pool up at the lowest point usually the brake callipers and cause the expected problems of water in caliper. Thats what makes it a poor choice on the street. Race cars will not go a year or more without systems being dissassembled and flushed.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

from somebody who just replaced all the soft brake lines and rebuilt a sticking caliper, changing the fluid is just the easiest and best thing to do. im definetly on the 2 year change interval from now on! especially compared to the PITA of cleaning up a corroded caliper, or the cost of replacing when rebuilidng is no longer an option!