Re: "I would not recommend using a silicone brake fluid regardless of what others may

[pmdolan]

Re: "I would not recommend using a silicone brake fluid regardless of what others may suggest."

Not to be contrary, but does anyone have a reason that they can back up with any credible information as to why they would not use silicone brake fluid? I hear guys give it a bad rap because another old timer (who I'm sure knows nothing about it) said, "no, only use dot 3". Harley Davidson has been using it out of the factory door for years. I don't hear about any bikers missing body members because of brake failure. I've been using silicone in my 1930 sedan for 5+ years in original copper brake lines with zero problems. It does not absorb water through condensation like DOT3 and 4. Since vintage cars do a lot of sitting, that can be the biggest problem. I've never had it destroy a pressure brake light switch (though, that is what some senior collectors tell me is going to happen if I use it). Maybe it's the $60-$70 a gallon that spooking some away from it. Maybe because you cannot get it off the shelf at most part supply stores. There is also a possibility that guys enjoy repainting firewalls and brake fluid reservoirs so much after splashing Dot3 on them, that they would not know what to do with the extra time if they made the switch.

I look forward to credible insight.

[Guest DeSoto Frank]

I used DOT-5 on the full-brake rebuild I performed on my '41 De Soto, about 12 years ago.

My motivation was the "fact" that DOT-5 Silicone fluids are not "hygroscopic" ( absorb moisture from the ambient air), and since the step-bore wheel cyls for my car were $50 each at the time, I wanted to prevent / delay future corrosion.

The only difficulties I had were in the initial fill & bleed-out of the system: I used a 1940's pressure-bleed tank which doesn not have a diaphragm to keep the air / fluid separate, and when I put air on the tank, I unwittingly created a "Dot-5 frappe`", which I then bled through the entire system. After three trips around the car with the hose & jar, I was still getting bubbly fluid and had a very spongy pedal.

I quit for the day, very discouraged. Next day, I called the fluid mfr's (Cartel) tech support, and discussed the situation with them; after walking through my fill / bleed proceedure, which should have been acceptable (for DOT 3 /4 ), the tech asked me about the type of bleeder tank, and "did it have a diaphragm"...

When I replied that "no, the tank does not have a diaphragm", he paused and said, "I think we've found the problem". He proceeded to explain to me that while DOT-5 fluid does not absorb moisture, it IS inclined to entrap air-bubbles, and that when I used my vintage bleeder tank, I had foamed my brake fluid, like some barista where $4 coffees are sold.

He recommended leaving the filler cap off the master cylinder for a few days (MC covererd with a clean rag), then slowly and carefully filling the MC from the bottle, taking care "not to glug the fluid", then slowly and carefully pedal-bleed the system with a helper.

I followed this suggestion, and successfully bled the system in two passes, and it has worked very well for the ensuing 12 years / 40,000 miles.

The other issue has been fairly rapid failure of the pressure-type stop-light switch; I've been through three new replacement switches (2 were KEM, the other one was Standard Ignition). They work for about two weeks, then would slowly deteriorate, requiring more and more pedal effort to actiatve the switch, finally requiring FAR more effort than was necessary to stop the car: essentially I was "driving without brake lights".

My solution to this was to abandon the pressure switch in place, and install a mechanical lever-type switch from a '47-'54 Chevy / GMC pick-up: this mounts to the underside of the toe-board, and the operating lever rides the brake-pedal arm. Never had a problem from this type switch.

Since doing the De Soto, I've done about three or four other full brake rebuilds and have used DOT-3 or 4 fluid.

I feel it worth mentioning that I was reading in the shop manual for my '61 Rambler last night, and American Motors recommends "draining the brake system, flushing with pure alcohol, and refilling with [DOT-3] brake fluid ONCE A YEAR."

That is the first time I can recall seeing a service interval specified for flushing / changing the brake fluid. If followed, I could see a DOT-3/4 system lasting much longer than we're used to .

( PS: we do have a 70+year history of how DOT-3 Glycol brake fluid behaves /ages, and what to expect from it - internal corrosion. RE: Harley guy - let's see, when did H-D start using hydraulic brakes... maybe the 1950's at the earliest? At any rate, I am sure Harley Guy is quite used to being able to pick-up any number of different catalogs and order whatever repro / aftermarket brake parts he needs for his Hog... not always that easy for us car guys...)

Edited September 17, 2009 by DeSoto Frank (see edit history)

[Larry Schramm]

I replaced the calipers on my Corvette and installed silicone brake fluid with no problems. in fact after replacing the calipers and bleeding the system, I had the best brake pedal that I ever had and have had no problems since.

As for changing the brake fluid, I know a number of oem's recommend that you flush the brake fluid at least every 2 years. Mostly it is the European manufacturers that note this recommendation.

[Steve Braverman]

Every motorcycle I have owned (there have been a lot, none American) has had regular brake fluid changes as part of the recommended maintenance. When the master cylinder failed on my BMW and leaked fluid all over the gas tank and my right knee, it was a painful $250 reminder as to why this is important.

I have never used DOT 5 fluid. A friend tried it in his 1930 Franklin and also experienced the DOT 5 frappe, but on the side of the road after climbing from sea level up into higher elevations.

[1929Chrysler]

After doing much research and speaking with reputable people who actually have vast experience in brake hydraulics, particularly Apple Hydraulics, I have drawn the conclusion that silicone brake fluid is perfectly OK to use as long as two issues are dealt with up front.

The 1st thing is that if you are converting from Dot 3 to silicone, there can be no trace elements of the old Dot 3 in the system. I believe even with a good flushing with alcohol you can't remove everything. Dot 3 and Dot 5 are not interchangeable and when mixed together turns into a big mess with certain brake failure to follow. In my opinion, if you are going to change over to silicone, your system should be brand new with every thing replaced so that there can be no possibility of mixing the two.

The 2nd thing that appears to be a common denominator with silicone problems is the use of cheaper silicone brake fluids. According to Apple Hydraulics, the majority of brake seal failures seem to come from the cheaper stuff. NAPA has been named a lot as a problem silicone fluid. Brake fluids have swelling agents that help the rubber to swell slightly enough to give a good seal. Seems as though the swelling agents in the cheaper fluid tend to attack certain seals and make them soft and "gummy" rendering their sealing properties non existent over time. A good quality silicone fluid would be "Cartel" as named by Desoto Frank. Their slogan is "Finally One That Works". I have been using it for a few years now with no problems.

Until some one with some type of engineering background can give scientific

reasoning as to why silicone should not be used, I am ready to put this silicone bashing to bed once and for all.

Dan

[Guest dgiorgi]

Well here's and idea...I always change the brake fluid every year. The dot type will absorb moisture as soon as the cap is opened. Thus changing the fluid every year is, in my opinion a must. But what to do with the old fluid? My Father told me long ago that brake fluid is a "natural rubber lubricant" I saw him use it on other rubber body parts under the car. Armed with this information, I use all the old dot fluid I remove and place it in a hand type spay bottle. Then every where there is a rubber motor mount or more specifically, body and suspension bushings, I spray them with the fluid. Of course you must take care with those autos with beautiful painted frames . In that case I use an oil can pump type. The rubber parts always soft and without crackes due to age and driving. Maybe it's me, but I feel the difference.

Hope this helps.

[Guest Tale Gunner]

Silicone Brake Fluid

The site has a article devoted to this question. Give it a look.

Vacuum Boosters Take a sample of silicone (I used gasket sealer years ago) and burn it with an acetylene torch. It oxidizes to a fine white powder. This is sand. If you have a vacuum-brake booster, some leakage into the engine is possible, so silicone brake fluid is not for you. Use glycol DOT 3 fluid to avoid an engine disaster. Any potential good from silicone is far outweighed by massive engine problems if it gets past the booster seals.

Use glycol DOT 3 fluid if you have a vacuum booster.

Quote from the article

[Amphicar BUYER]

Now for the untimate test I have used DOT5 in my Amphicars for 12 years now. No problems, nothing! The key is use it in a NEW system or a well flushed (w alcohol) system with all new rubber parts. DOT5 has been proven time and time again.

Changing the fluid every year is WAY overkill, but if it makes you feel better then at least you get that warm and fuzzy feeling.:cool:

[Curti]

I have used DOT5 brake fluid in all of my collector cars for the past 15 years. I was informed by a reliable source the rubber swelling problem that is incurred is an incompatiblity problem with silicone and type of rubber used old Wagner kits. Wagner is aware of this issue. DOT5 is mandated for many types of US government vehicles.

[Spitfire8]

I also heard that brake cylinders need to be smooth-finished, and not crosshatched in order to prevent DOT5 from leaking past the seals.

[Roger Zimmermann]

Brake fluids have swelling agents that help the rubber to swell slightly enough to give a good seal.

Dan

I never heard that, but, fortunately, I don't know all. In fact, the master cylinder is equiped with a residual check valve; this valve maintains a small pressure in the circuit to prevent that the brake fluid pass the seals when the brake pedal is not applied.

My 3 Cadillacs have DOT 5 brake fluid; I have no problem with that fluid and would not go back to the DOT 3 or 4.

[Ben Bruce aka First Born]

I started to not enter into this frsy, but it is just too tempting. I have never used DOT5. Did not even know it wxsited until this forum came onto my radar screen. Having said that, I guess ignorance is bliss. I have owned my 1978 Dodge PU since 1996 Had to redo the brakes shortly after buying it. A couple months ago I had to replace the master cyl. It was leaking by inside. Fourteen years!! In 1996, used DOT 3. Am I just lucky??

In 1997, I bought my 1977 Cadillac. Have done nothing to the brakes on it.

Should I have changed the fluid yearly as some propose? Well, shame on me, but I believe I am way ahead. And so is the enviroment as I had to dispose of nothing.

By the way, boyh are daily drivers.

Ben

[Ben Bruce aka First Born]

Well, my cars perform better than I. Should have edited!

Ben

[Guest Backyardmechanic]

Bruce,

That is the whole story being driven everyday.The problem begins when the car/truck has set in storage for a given time.

Vern

[Guest Adam4t]

I've never experienced DOT5 brake fluid. From what I read in the other posts, it sounds like a lot to go through just for a different type of brake fluid, in my opinion.

From all my experience, DOT3 has worked fine, but DOT4 doesn't seem to do the job as well.

[1936 D2]

OK. I will weigh in here. I did a full brake job back in 1986 on my 1936 Dodge with stepped brake wheel cylinders. I figured, since I was going to do the whole system, and that there would be a lot of "sitting" time on a vented system, I would use the fluid that is non-hygroscopic (wouldn't absorb water). I was appalled by the condition of the brake system as I was repairing it. The interior rust problem was bad. This, of course, was from the DOT-3 fluid originally in the system. I resurfaced all wheel cylinders (kind of a pain because of the stepped nature of the cylinders), the master cylinder, replaced all the long lines and rinsed with alcohol the short line through the frame under the radiator. The system was "pedal-bled".

All parts were replaced with "over-the-counter" Wagner wheel and master cylinder kits. The original hydraulic brake light switch was NOT replaced because I did not have a new one at the time. (It is still in there). I do not use it because it was not working quick enough but not leaking. I use an external lever switch mounted under the floorboard by the pedal linkage for the lights.

This system has been in place for 20 years now. Fluid was never fully replaced. The system was topped off twice in the 20 years. I am suspecting the loss was through the old brake switch top. Hard to tell. I am due for a shoe adjustment but otherwise I can lock up the brakes and skid the tires if I want.

I am "sold" on silicone DOT-5 brake fluid and will not go back!

PS: I have clearly marked the top of the master cylinder "DOT-5" so no mistake is made. I have also carried extra fluid with me in the trunk all this time. (Just in case!) This extra fluid is also in its original container and condition with no color or odor change and was used to do the "top offs" when necessary. (Let's see the DOT-3 fluid do that!)

Have a good one!

[Larry Schramm]

Here is a great article on brake fluid & corrosion.

http://www.brakestrips.net/docs/industry_adopts_brake_fluid_replacement_guidelines.pdf

[Steve Braverman]

I am about to go through everything on my '32 Plymouth. Will the vented cap on the master cause the DOT 5 to absorb air?

[1936 D2]

Air NEEDS to be there. That's why the cap is ventilated.

I think your question would be: "Will the vented cap on the master cylinder cause DOT-5 to absorb water?"

Answer: "No". DOT-5 does not absorb water. It is Non-hygroscopic. That is one of the attractions of DOT-5!

The cap vent IS one of the places that water gets into DOT-3 and DOT-4 fluid though. But the vent NEEDS to be there for the master cylinder to operate properly.

To be fair though, the research has shown that water is not the biggest problem with brake fluid contamination, copper is. I personally feel that silicone fluid (DOT-5) has less of a problem with free copper in it than DOT-3 fluid, but I have not seen research that specifically addresses that. There IS a good section of research that DOES show free copper (regularly found in the fluid mainly from the coating inside the brake lines) causes higher corrosion inside the system particularly in the master and wheel cylinders made of ferrous metal. (Those parts sleeved in stainless, of course, are not as susceptible).

See: http://www.brakestrips.net/docs/industry_adopts_brake_fluid_replacement_guidelines.pdf - for more info on the copper issue and how to test for it.

I did not sleeve my master and wheel cylinders. They are raw ferrous metal. I also replaced most of the brake lines (like 80%) with new material that I understood had a copper content inside. Even with both of these "possible" contributors to issues I have not observed any detrimental affect to my system in the many years I have been using DOT-5 fluid.

One thing TO watch though is foaming of the DOT-5 fluid. It accepts air fairly easily from cavitation. So, be gentle when pouring, don't shake the bottle and pump slowly when bleeding. If you do foam it up, just let the system sit open (with a rag over it) for a day or so. The air will eventually "stick together" and work it's way out. (There is more info about this in that paper from the link above.) Suffice to say, just don't be violent with your DOT-5, and it will be nice to you. It will not cavitate under normal use in the system.

Have at it!

Edited April 24, 2010 by 1936 D2 (see edit history)

[Restorer32]

A minor correction..."hygroscopic" actually means " readily absorbs water". The advantage of DOT 5 is that it is NOT hygroscopic.

[1936 D2]

Oops! Fat fingers! :eek:

Thanks!

Edited April 24, 2010 by 1936 D2 (see edit history)