A few excerpts from a tech article I wrote for the Valley Oak Porsche Club (CA.) in 1998.

I started using DOT 5 in 1981, when the only company to make it was general Electric. I first used it during a complete overhaul in my 1970 ElCamino. 7 years later and over 100,000 miles later, you could still see right to the bottom of the master cylinder and bleeding at each wheel yielded clean fluid. When we broke the system down for curiosities sake, everything looked new and the pistons showed no trace of wear.

From that time on, we used it in everything, tractors, tow vehicles, motorcycles & race cars and we enjoyed outstanding results.

We have all heard that DOT 5 fluids are compressible, but in reality, I have experienced a more solid pedal with 'properly installed' DOT 5 than I ever had with 3 or 4.

Why do we continue to use a fluid that has been around since the automotive dawn of time?

Let's look at a real-world, non-scientific case study.

We had a 1974 Toyota truck that was used by the shop to run errands. At least once, and sometimes twice per year, we would have to replace the clutch master and slave cylinders, Inspection would reveal badly worn bores and pistons.

We decided to convert the clutch system to GE DOT 5 and after that change, we drove the truck 10 years without replacing either the clutch master or slave cylinder.

So who uses it???

The Military and U.S Postal Service to name but two, but let's look deeper ito the widespread disadvantages of DOT 5 silicone fluids.

Compressibility

Detractors say one of the first disadvantages of silicone brake fluid is compressibility. You don't want any compressibility in your braking system. This will cause your brake pedal to feel soft when you press it. Silicon brake fluid is slightly compressible and will cause this softer pedal more than glycol based fluids.

Moisture

Fact is that all braking systems have moisture in them. Other types of fluid absorb water easily. Unfortunately, silicone brake fluid does not absorb water. Detractors say since the water does not mix with the fluid, it will descend to the lowest point and form a puddle. This can lead to corrosion in your hydraulic system and may impair the functioning of your brakes.

Compatibility

Detractors say another disadvantage of silicone brake fluid is that it is incompatible with glycol-based fluids. This means that you will not be able to mix the two types. If your car has used glycol-based fluids for a long time, you will have to flush and reseal the entire system to use silicone brake fluid.

Anti-lock Brakes

Detractors say silicone brake fluid also can't be used with many anti-lock braking systems. Most systems are designed to work with glycol-based fluid. If you use silicone brake fluid instead, it may interfere with the mechanical valving found in some anti-lock braking systems.

Most all of the claimed disadvantages can be addressed simply by reading FMVSS 116 and SAE J-1703.

Since silicone doesn't draw moisture from the air, it is highly unlikely that you will get water in your system in the first place.

Secondly, DOT 5 must be 100% compatible with DOT 3 & 4 and ALL seals used in DOT 3 & 4 systems. While mixing the fluids will reduce efficiency, it can be done.

Compressibility is the #1 scare tactic used. I have raced with this fluid at speeds up to and exceeding 152mph with enough heat on the brakes to turn turn the rotors red and the pedal was consistent.

Read this about silicon fluid composition from an SAE technical paper:

"Specially formulated, DOT-5 high-temperature fluids reduces corrosion in the braking system. Provides even braking performance in temperatures from -75 degrees Fahrenheit to +600 degrees Fahrenheit. Recommended for Domestic, European, and Japanese vehicles. Excellent for motorcycles, heavy duty vehicles, and trailer units."

Hmmmmm.....

It has been said that compressibility makes it unsuitable for use in ABS systems, according to Bendix, but other manufactures (like Lucas-Girling and ATE) claim it 'aerates' when cycled rapidly through small orifices in the ABS system.

Aeration cannot take place in an airless environment. It's just that simple. While the jury is still out on DOT 5 in an ABS systems (I am yet to test it in ABS since my 911R and 911S lack those systems) I won't comment further, but let's explore a couple of things.

DOT 5 is slow to disburse bubbles when compared to DOT 3 & 4. My theory, based on my experiences with DOT 5 is the soft pedal is a direct result of operator error in the installation.

Would the military or postal service accept a spongy pedal? I doubt it very seriously and the SAW and FMVSS both specify that pedal travel and feel may not change among the various fluid types.

One advantage of silicone fluids is their longevity, lubrication of braking components and corrosion resistance. Put DOT 3 or 4 on your fingers and snap them, then try it with DOT 5. Feel a difference?

That black 'mud' you see in a master cylinder is many things, such as water and particles of rubber shaved off the seals every time you press the brake.

So, why not use it???

Look at the major detractors trying to frighten people away from silicone fluids - manufacturers of brake parts!


Why would Bendix or Lucas Girling recommend a product that can and has doubled, even tripled the life of a brake system, times many hundred thousands of consumers worldwide?

But wait! Major race teams don't use it....

And why is that?

What sponsor would want to advocate a fluid or any other product that will make itself at least partially obsolete? Thiunk about how many master cylinders you have replaced and multiply that times 100,000's and look at the economic impact using silicone fluids would have.

It's more about marketing strategy than anything else, so your decision needs to be an informed one.

If you want DOT 3 or 4, follow directions and change it at least yearly. If you want DOT 5, install it according to directions and enjoy.

I am using it in both my street driven 911S and race/street 911R with many, many thousands of stops. As always, feel free to contact me if you have any questions, suggestions or concerns.

See you at the track.....Bert

Attached Thumbnails

 

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

I have used DOT 5 in all my non-ABS cars since 1992, including my 300D's. I just pulled the cast-iron MC from my 65 Newport that I installed new ~1993 (w/ DOT 5). It looked brand-new inside. I removed it to install a dual reservoir MC (safer). With glycol fluid, I dealt with rust gunk and pitted wheel cylinders (lived in Georgia).

You read amazing statements about silicone brake fluid. Some are quite humorous. Some after-market companies even state that mixing it with glycol will cause solid chunks. This was tested and found untrue (search web). If you leave any glycol, that is just places where you can get rust. I also wonder why manufacturers say not to use it with ABS. I wonder if they just never tested it, so their lawyers tell them to say that. I would rather have an ABS box that works even if at 95% performance, rather than one gunked up with rust from glycol fluid. Maybe I'll try DOT 5 in those cars.

A few other brake fluid misunderstandings:

DOT 5.1 is not silicone, it is bad, rusty glycol. It is the first glycol mixture that meets the higher DOT 5 standards. The government had them designate it 5.1 to not confuse it with silicone, though guess how well that works.

"Synthetic" brake fluid is not better. All brake fluids are synthetic (i.e. man-made, not naturally occurring minerals). Some marketing geniuses figured they would leverage public stupidity about science.

I wish more people would use DOT 5. As is, it is getting rare and expensive. I have a gallon of military surplus, but it is getting low. It is the only brake fluid the military uses, because it is a bad day when they get stranded. Also, a bad day for any driver when their brakes don't work.

Nice post, Bill...

It's hard to argue with results.

My 2001 Mustang ABS/TRAC will be getting DOT 5 as soon as I do a complete brake rebuild....

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Not true. Humvees get DOT 5. Other juice brake systems are still using DOT 3, except for the odd piece of heavy construction equipment with mineral based brake fluid, and of course all the stuff we have with air brakes. Remember, air is a fluid as well: Fluid - Wikipedia, the free encyclopedia

I'm not saying DOT 5 is bad or not worth it. I simply haven't used it in anything besides a Humvee. I wouldn't call the pedal feel in a Humvee spongy, but compared to my Mercedes I would call it vague. I spent two weeks earlier this month putting a couple hundred miles on an M1152 in between other duties. The pedal feel on the (otherwise mostly likeable) Kia Forte rental car I had was worse.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I have a 1999 s320 with abs.What should I use,or what is superior as I drag race.Already running ceramic pads?

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

I've always been leery of DOT5 on the water stories, but I'll take the Doktor's advice and try it out next time I service my brakes.

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

An aquaintance of mine has a 39 Chrysler partially restored and sitting for over twenty years. The brake system was restored and type 5 fluid used. The brakes still work the last time he checked them.

I am pretty sure with type 3 or 4 fluid they would have issues by now. I think many systems if any are not really tight enough and the older fluids being seriously hydroscopic in nature causes a of of grief with sitting vehicles.

I too visualize that brake component manufactures would lose a lot of business if type 5 was universally used. The added lubricosity was something I was unaware of and a real upside as well.

The water absorption of types three and four is a serious issue. They even attract moisture. I have some type 5 on a shelf.

I have not used it as keeping a system sealed was quoted as an issue years ago. But if everything is redone the systems seem to hold it well. It was even recommended back then that all seals in the system be renewed first if bores where good.

I have cars sitting around long periods between uses so I think I will convert some of them. Glad this subject was posted as it got me thinking again about those conversions.

Until I PERSONALLY test DOT 5 in an ABS system, I cannot recommend it to anyone.

For your S320 I would recommend ATE Dot 4 Class 6 which is rated for ABS and ESP systems...Robert

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

We used this stuff in everything and that is the only reason why I posted my opinions because it is from actual use in everything from tractors to race cars.

We used to maintain an old Fire Truck for a friend's ranch that had hydraulic (go figure) brakes and every couple of years, the pedal would go to the floor and we would have to redo the brakes, even with a fluid change seasonally.

One year (1990) I did the M/C and all the wheel cylinders brand new and used GE DOT 5 fluid.

They spoke to my Dad last week about how they are still driving it and have never had a brake problem since the fluid change.

That event, and my recent $400.00 brake job on my 300SD, jot me rethinking the DOT 5 controversy and inspired this post.

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

With DOT 5 the fluid makers do not recommend changing fluid until you open the system for repairs.

I have bled small samples from my cars and never got anything but purple fluid out of them.

Since DOT 5 does not ABSORB water from the air, you would literally have to pour water into the system to introduce it...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Follow the directions, as you need a complete removal of the old fluids to get the full benefit of a DOT 5.

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

there is one other important reason to use Dot 5 fluid...

it does not harm paint.

ALL show cars that have exotic paint on them use Dot5 for this reason alone.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Wiki - "Unlike polyethylene glycol based fluids, it is hydrophobic. An advantage over other forms of brake fluid is that silicone has a more stable viscosity index over a wider temperature range. Another property is that it does not damage paint[citation needed].

Using DOT 5 in a DOT 3 or DOT 4 system without proper flushing will cause damage to the seals and cause brake failure[citation needed]. DOT 5 brake fluid is not compatible with anti-lock brake systems. DOT 5 brake fluid absorbs a small amount of air requiring care when bleeding the system of air.[citation needed]"

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Read Federal Motor Vehicle Safety Standard 116 (lengthy) which requires DOT 3, 4 & 5 to be compatible with ALL seal materials used in glycol brake systems and that DOT 3, 4 & 5 be able to mix, even though boiling points would be reduced.

Also, DOT 5 does not absorb air, but rather it holds bubbles in suspension longer than glycol when shaken.

Again, operator error...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership