Change to silicone brake and clutch fluid

[n/a]

I am getting ready to put my 1965 230 SL to bed for the winter.  I am going to change from conventional brake fluid to silicone.  If I don't get ALL of the old dot 4 out of the system, will the silicone gel or cause any problems with the older conventional brake fluid?

TY
Rupert

[113gray]

Please think carefully before switching to silicone brake fluid. I have it now in 2 MB's & am going to switch back to DOT 4 as soon as I can. I have heard the pros & cons of this argument for many years, but an experience last weekend made me decide to go back to Dot 4. I toured a famous antique auto restoration business that has been operating under 3 generations of one family for many years. They also have a significant portion of thier business in repairing/rebuilding brake cylinders, boosters & relining shoes. They see many examples of brake damage, especially to rubber diaphragms & seals, from silicone & have stopped recommending it for any brake application. In addition, no auto manufacturer recommends it, including Mercedes. I have just replaced a brake cylinder in one of my cars that was essentially destroyed by moisture. This car has had silicone fluid for 10 years so obviously the silicone did not protect against moisture in this case. I have come to believe the best fluid is Dot 3 or 4 changed every 2-3 years. Good luck.    -JP-

[rwmastel]

I just bought some brake fluid a couple weeks ago and was going to put it in this weekend.  I may return it and get regular DOT 3.  I bought Valvoline SynPower Brake Fluid.  It describes itself as:

"SynPower ABS synthetic DOT 3 & DOT 4 motor vehicle brake fluid recommended for anti-lock braking systems, hydraulic drum and disc braking systems and hydraulic clutches requiring DOT 3 & DOT 4 fluids.  It's premium, synthetic, low moisture formulation provides superior anti-vapor lock protection.  Has a high dry-boiling point up to 502F that reduces the risk of fluid vaporization and possible brake failure.  Meets and exceeds specifications SAE J1703, FMVSS No. 116 and DOT 4 Motor Vehicle Brake Fluid.  Surpasses Federal Motor Vehicle DOT 4 requirements.  Mixes with conventional brake fluids.  Minimum wet boiling point of 343F.”

What do you have to say about synthetic brake fluid? I would like to hear more opinions and experiences.  Here's what our Technical Articles say about brake fluid:
http://www.sl113.org/articles/brakes/brakes.asp

I am interested in silicon brake fluid since I am replacing all the lines, etc. during the restoration. Is silicon fluid an improvement over DOT 4 or 5? Or is the main advantage longevity of the fluid?

I struggled with this when I restored my brake system. My restoration shop advised against it, believing that my reconditioned brake booster and rubber components exposed to the synthetic fluid (silicon?) would not hold up and I would have problems. Any long-term users of synthetic fluid for brakes?

I use silicone fluid (DOT-5) because the brakes on my car faded when coming down an Alpine pass on its maiden voyage, then again a year later in an MBCA time trials. Therefore I consider it a handling enhancement.

I have had both good and bad luck with synthetic brake fluid. I used it in a 190 SL and my 280 SL. Both did just fine. I used it because it was the in-thing to do. Both cars had new brake systems. The only used part on the 280 SL was the proportioning valve by the gas tank. I have also tried the synthetic on a customer's 190 SL and had the fluid pour right out of new wheel cylinders. What a mess. Changed the wheel cylinders and it happened again. Perhaps it was the fluid. I was told only Dow and GE make the stuff. The only reason to use synthetic that I can see is it will not mess up your paint. Otherwise, the brake system still collects contaminants such as moisture, dirt, and old rubber. Which means you have to bleed the system every few years to get clean fluid in there. I think there is less possibility of rubber flex hoses swelling up internally. That would be a plus for synthetic. The higher boiling point is not a factor unless you race your car. I did get a slightly spongy pedal with the synthetic, but I got used to it.

I have been using silicone Brake Fluid (I.E.: DOT 5) for probably 20 years. I've only had a problem on one car, 70 Barracuda Convertible, that I just flushed the system and the Wheel seals leaked. This is because it does not swell the wheel seals. After installing new wheel cylinders it worked fine. You've overlooked one main advantage. Silicone Brake Fluid is hydrophobic, it does NOT absorb water (I see no need for annual flushing.) Standard DOT 3 brake fluid absorbs water from the atmosphere, breathing from the Master Cylinder lid. This is why the DOT 3 containers all state that it must be kept sealed. In my experience the main cause of failure of wheel cylinders on shoe brakes is the corrosion at the bottom of the cylinder from water droplets. I admit that disc brakes run at a higher temperature and are not as subject to this (my '67 230 SL still has shoe brakes on the back). But, although it will mix with DOT 3, there's no advantage unless you're rebuilding the system and everything is clean, without moisture. Silicone will not take the water out of an old system.


Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[George Davis]

My 3 pfennigs worth:

The synthetic brake fluid sounds like it's just a "better" DOT 3 or 4 fluid, although it also sounds like just a marketing ploy.  Brake fluid is pretty much ethylene glycol (like antifreeze), which is manufactured in a chemical process... therefore all brake is synthetic whether it's labeled synthetic or not.  But, it may be a better brake fluid, similar to racing brake fluid (see below).

Silicone brake fluid doesn't absorb moisture like regular brake fluid.  But, this doesn't mean that moisture can't get in the system.  It can and will, but it will remain in a separate phase and could puddle somewhere and cause localized corrosion.  I agree completely with 113gray that DOT 3 or 4 (I use DOT 4) flushed every couple of years is the best approach.

Last, if brake fade is a problem, try racing brake fluid.  One cause of brake fade is boiling the brake fluid, which creates bubbles so it acts just like there is air in the lines.  Racing brake fluid is available as DOT 4, but has a higher boiling point.  It makes no difference in normal driving, but if you're running your brakes very hot for some reason (racing or lots of long downhill stretches), this stuff really makes a difference.

George Davis
'69 280 SL Euro manual

[n/a]

Here's some food for thought...Mercedes-Benz recommends that you use DOT4 fluid and change it yearly. I think if there were a better fluid they would specify it. Ferrari et al also use standard brake fluid DOT 4, and recommend changing it yearly. I do this in all my cars, and particularly the ones that are laid up in the wintertime and not driven; I believe that disuse probably hurts a braking system worse than anything else does. Periodic heating helps displace moisture if nothing else..
  Leaving brake fluid in past its time causes corrosion and poor functioning in braking systems. This is the reason that to get a car out on a track day, all the car clubs insist on a tech inspection that verifies that you have had the brake fluid changed and the system inspected within a year- it cuts down on brake failures on the track. I think yearly brake fluid changes are cheap insurance, especially on cars like SLs that tend to spend the winter indoors and not get driven for long periods of time. The Ferrari club bulletin also suggests that when a car is stored, you cycle the brakes every few weeks and thus keep the seals from sticking.

[Malc]

Lot of pros and cons re silicon brake fluid but here are my experiences....

Used Silicon brake fluid in my 1962 MGA (fluid 4 years old)and my 1974 BMW2002Tii,(3 years old) however in both cases I had completely rebuild the braking system on both cars.
To date I have had no problems with it in either vehicle and the Beemer is notorious for sticky calipers, but so far nothing has happened.
No leaks or seal problems so far.

Pedal MAY seem slightly "softer" with this fluid.

You can mix it with regular brake fluid, but the benefits will be lost.

Reason all car companies use DOT 4 is because it's cheap. and "its always been done that way"

problems associated with it are mainly regarding painting as it causes "fish eyes" in the paint. this problem is common to all silicon products including car polish, WD-40 etc. It is difficult to remove, however a steam cleaner with TFR (Traffic Film Remover) chemicals will work and rip all the polish off the car too!

In my rally car I use Mintex Racing Blue fluid mainly due to it's very high boiling point as I left foot brake most of the time.

Finally it is a myth that warming the brakes up will displace any absorbed water as the pipes, master cylinder, servos etc remain pretty cold. If you stick to DOT 4 change it at least every 2 years and more often if you live in a damp or humid climate.

Don't use DOT 3, except in agricultural machinery it's rubbish for a fast road car,thats why DOT 4 is now the norm.

End of my rant
Malc
Scotland