Topic: What do y'all know about synthetic brake fluid? Is it safe for our older cars?

[michaeld]

I'm just about to shut her down and go to bed, but...

In the morning I plan to install a new master cynlinder (although I'm a little confused about the process of bench bleeding my M.C. w/ the vacuum method), and of course need to replace my brake fluid.

I got my fluid at Autozone.  Everything was cheap junk that I didn't want in my baby except Valvoline SynPower synthetic (DOT 4, of course).  It exceeded all of the specs (SAE J 1703B and FMVSS #116) that the MBz Technical Manual indicated.  I've never used synthetic brake fluid before - and always worry about the word "synthetic" with an older car.  Has anyone had any horror stories with this stuff, such as new leaks they're sure they wouldn't have had if they'd just used "regular" stuff?

And also, isn't ordinary brake fluid synthetic?  I'm pretty sure it's not hydrocarbon-based.  Are we fighting over polyethylene glycol wells somewhere in the Middle East, and I just don't know about it?  Is synthetic brake fluid just a marketing gimmic, or is it somehow more "synthetic" than ordinary brake fluid? 

[Denis]

Hi Michaeld

I did put synthetic fluid in my W109 three years ago and the seals went bad BUT they were going in any case. I just hastened their demise. New seals in the calipers, complete flush and synthetic brake fluid all sung a nice tune from there on. The master cylinder was a recent one also.

Simply put : you might get leaks but if you are going to R&R, definitely do it as the synthetic fluid is NOT hygroscopic (absorbs water) and the system remains corosionless 

I wonder if the material in recent seals is not designed for synthetic ?

Denis

Paris, France

[michaeld]

Gosh, Denis,

Your post had the opposite effect of providing me with the reasurrance I was looking for, as I have no intention of rebuilding calipers!  In fact, your post kind of reminded me of that "the operation was a complete success, but the patient died" line.  If your situation is typical of running synthetic in an older car, then I would prefer going to the time and trouble of ordering ATE Blue from some distant realm.

Has anyone switched to synthetic brake fluid and NOT had to install new seals in their brake system?

 

[Denis]

Hi michaeld

I have a note of optimism for you.

There are two kinds of synthetic brake fluids : on IS COMPATIBLE with regular brake fluid and one is NOT.

I used the NOT, it has better performance but you might want the use the  "IS COMPATIBLE".

The problem is finding it. Most chain stores do not have staff that can tell the difference. Most real mechanics know the difference so I suggest that you ask someone that rebuilds brakes.

Feeling better ?

Denis

Paris, France

[116.025]

Valvoline SynPower doesn't seem to be a problem.  My dad and I put it in both of his 126s and his 111 when we did brake fluid flushes on them after installing new pads and rotors.  Maybe I'm not remembering correctly, but the synthetic stuff that isn't compatible is usually labeled DOT 5, and says something about being silicon based and not for use with other fluids, (and is the one that's not hygroscopic) right?

[michaeld]

Denis and 116.025,

Ah, now we venture into the sunlighted climes of Happy happy land!
Yes, there are apparently THREE categories of brake fluid now: the standard polyethylene stuff, synthetic, and silicone.  Silicone is DOT 5, and is a very serious no no according to the MBz Technical Companion because it causes corrosion in our systems (something about a complete inability to absorb moisture, thus trapping moisture as a single entity in your system).

I looked at the Valvoline SynPower (DOT 4); it is compatible with all the standards that it's supposed to be compatible with.  I was just fearful that it might result in leaks in older systems (like the synthetic engine oil can contribute to).

Is the final verdict, DOT 5 synthetic (silicone) bad; DOT 4 synthetic good?