• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Silicone Brake Fluid

j-c-c-62 said:
But my real point was, that long known observation seems to be mostly ignored and avoided by silicone advocates.

"Why is the topic of why EXACTLY silicone BF's are not allowed with ABS would I suspect be rather telling.
Click to expand...
I am not catching what you're getting at? It's not used because the frequency of the solenoids in an ABS hydraulic unit coupled with the pump agitation, causes the fluid to foam. DOT 5.1 is also synthetic and does work with abs. Neither one works in a power steering box either, but that doesn't mean a thing. It's not a debate topic, no right or wrong, it's preference, plain and simple. I went with it because my cars sit a lot and I don't want moisture from our humid climate to cause any issues with my brake system investment.
 
"I am not catching what you're getting at?"

I am getting at why are the downsides to silicone seldom if ever mentioned? It aerates, and it is compressible, relatively. Nearly every solution has a downside. You are the first here, #21, to post one of them. Is that acceptable by some/many, sure, but it's best if they know it first, and that means it must be part of the discussion, and that is rare, IMO.

Debate would mean I disagree, not ask a question. I will however question the premise that humidity is the source of BF moisture absorption that causes brake fade/corrosion. I'd like to see the research that explains how prevalent air borne humidity is that enters a somewhat sealed MC and travels many feet thru a fairly small steel tube to the heat source (caliper) that boils said moisture. when the fluid only moves an inch or so back and forth in normal use. We are for clarity ignoring the bleeding of any possible moisture laden BF from the MC down to the brake cylinders/calipers. I lean towards most moisture issues with BF are from very old BF, or cars driven in the rain and parked wet, or deep puddles, entering the system from the caliper end, especially regarding corrosion, which we have all seen.
 
j-c-c-62 said:
"I am not catching what you're getting at?"

I am getting at why are the downsides to silicone seldom if ever mentioned? It aerates, and it is compressible, relatively. Nearly every solution has a downside. You are the first here, #21, to post one of them. Is that acceptable by some/many, sure, but it's best if they know it first, and that means it must be part of the discussion, and that is rare, IMO.

Debate would mean I disagree, not ask a question. I will however question the premise that humidity is the source of BF moisture absorption that causes brake fade/corrosion. I'd like to see the research that explains how prevalent air borne humidity is that enters a somewhat sealed MC and travels many feet thru a fairly small steel tube to the heat source (caliper) that boils said moisture. when the fluid only moves an inch or so back and forth in normal use. We are for clarity ignoring the bleeding of any possible moisture laden BF from the MC down to the brake cylinders/calipers. I lean towards most moisture issues with BF are from very old BF, or cars driven in the rain and parked wet, or deep puddles, entering the system from the caliper end, especially regarding corrosion, which we have all seen.
Click to expand...
I would disagree based on my 50 years of working on vehicles. Brake fluid by its chemical nature is hygroscopic. It absorbs moisture. You are saying that water would 'boil off', which is absurd an assumpton because the moisture has reacted with the fluid and cannot 'boil out', if it did, it would create a gas bubble in the brake system and you'd lose hydraulic pressure in the system as a gas can be compressed. The moisture is homogeneous throughout the hydraulic system, turning the fluid corosive. Moisture gets into the system, plain and simple. Let's address that fact that doesn't get discussed about DOT 3 and 4 fluid, it degrades over time as humidity(water) makes it's way into the system. The master cylinder covers on our old cars were notorious for leaking fluid, that means that moisture in the air can also make its way into the fluid. This causes it to rust from the inside out. According to your view of the system, brake fluid would never need changed, parts would never wear out and brake lines would never rust through. It is possible for moisture to wick into the system, yet fluid to not come out due to the very nature of the lip seals used in wheel cylinders, master cylinders and calipers.
 
j-c-c-62 said:
But my real point was, that long known observation seems to be mostly ignored and avoided by silicone advocates.

"Why is the topic of why EXACTLY silicone BF's are not allowed with ABS would I suspect be rather telling.
Click to expand...
Not sure I’m following you, but none of my 4 old cars have anti-lock brakes so it’s kind of a non-issue for me. Works great in my 2 MY66 cars.
 
AR67GTX said:
Not sure I’m following you, but none of my 4 old cars have anti-lock brakes so it’s kind of a non-issue for me. Works great in my 2 MY66 cars.
Click to expand...
I don't dispute your claim, but silicone remains compressible and aerates no matter what the system it is used in.
 
Nxcoupe said:
I would disagree based on my 50 years of working on vehicles. Brake fluid by its chemical nature is hygroscopic. It absorbs moisture. You are stating the obvious, but you have not addressed how the amount of hygroscopic effect is had by a single pin hole vent on the top of the MC and that absorption travels many feet thru a small steel tube all the way to the caliper which is the ONLY heat impacted component of the brake system, understanding the fluid is effectively static except under application when it might move bidirectionally an inch? You are saying that water would 'boil off', which is absurd an assumpton I never said "boil off" because the moisture has reacted Not sure if it really "reacts" I submit it does not with the fluid and cannot 'boil out', if it did, it would create a gas bubble water boils at much lower temp and why it is anathema to a brake system in the brake system and you'd lose hydraulic pressure in the system as a gas can be compressed. That "boiling" you note" is however the often cause of heat brake fade, no matter what the condition of the brake fluid is The moisture is homogeneous throughout the hydraulic system Can you support that claim?, turning the fluid corosive at what point of "turning" can you support that claim?. Moisture gets into the system, plain and simple. How? Let's address that fact that doesn't get discussed about DOT 3 and 4 fluid, it degrades over time as humidity(water) makes it's way into the system. I submit the small amount moisture that might travel very slow if at all thru the lines and causes little if any harm until somehow it reaches the calipers or wheel cylinders The master cylinder covers on our old cars were notorious for leaking fluid, that means that moisture in the air can also make its way into the fluid. This causes it to rust from the inside out That effect is caused best by consolidated water sitting in a brake line at one spot for a length of time, and hence why the hygroscopic effect is useful because water cannot coalesce for long in one spot inside a brake line, it is absorbed and diluted. According to your view of the system, brake fluid would never need changed I never said that, parts would never wear out and brake lines would never rust through. It is possible for moisture to wick into the system, yet fluid to not come out due to the very nature of the lip seals used in wheel cylinders, master cylinders and calipers. I agree, but I can't prove that, you are welcome to. I addressed by my mention previously water might enter the caliper/wheel cylinder by water immersion and/or wet driving, and parking the car wet before the moisture could be heated out of the seal area by driving/braking.
Click to expand...
 
Last edited:
Omg, I am not stating an opinion. I won't waste my time with my credentials. It permeates throughout the system. It doesn't boil off for the same reason it doesn't boil off from anti freeze. Do you even know what brake fluid is made of? I do. Polyglycols. Meaning, multiple types of xxglycol mixed together, one being ethelene glycol, ring a bell? Yep, anti freeze. I'm not going to let you drag me down to your level and beat me with experience in an argument. Enjoy your blissful ignorance and have a wonderful day! I will be ignoring further comments, I win!
 
Nxcoupe said:
Omg, I am not stating an opinion. I won't waste my time with my credentials. It permeates throughout the system. It doesn't boil off for the same reason it doesn't boil off from anti freeze. Do you even know what brake fluid is made of? I do. Polyglycols. Meaning, multiple types of xxglycol mixed together, one being ethelene glycol, ring a bell? Yep, anti freeze. I'm not going to let you drag me down to your level and beat me with experience in an argument. Enjoy your blissful ignorance and have a wonderful day! I will be ignoring further comments, I win!
Click to expand...
Other than a personal attack, you have shared nothing more than your anger and inability to address my specific counterpoints.
Maybe if you take a short time out, you might be able to rejoin the conversation less hostile later.
Ignoring is related to "blissful ignorance" I am told.


Nxcoupe said:
I would disagree based on my 50 years of working on vehicles. Brake fluid by its chemical nature is hygroscopic. It absorbs moisture. You are stating the obvious, but you have not addressed how the amount of hygroscopic effect is had by a single pin hole vent on the top of the MC and that absorption travels many feet thru a small steel tube all the way to the caliper which is the ONLY heat impacted component of the brake system, understanding the fluid is effectively static except under application when it might move bidirectionally an inch? You are saying that water would 'boil off', which is absurd an assumpton I never said "boil off" because the moisture has reacted Not sure if it really "reacts" I submit it does not with the fluid and cannot 'boil out', if it did, it would create a gas bubble water boils at much lower temp and why it is anathema to a brake system in the brake system and you'd lose hydraulic pressure in the system as a gas can be compressed. That "boiling" you note" is however the often cause of heat brake fade, no matter what the condition of the brake fluid is The moisture is homogeneous throughout the hydraulic system Can you support that claim?, turning the fluid corosive at what point of "turning" can you support that claim?. Moisture gets into the system, plain and simple. How? Let's address that fact that doesn't get discussed about DOT 3 and 4 fluid, it degrades over time as humidity(water) makes it's way into the system. I submit the small amount moisture that might travel very slow if at all thru the lines and causes little if any harm until somehow it reaches the calipers or wheel cylinders The master cylinder covers on our old cars were notorious for leaking fluid, that means that moisture in the air can also make its way into the fluid. This causes it to rust from the inside out That effect is caused best by consolidated water sitting in a brake line at one spot for a length of time, and hence why the hygroscopic effect is useful because water cannot coalesce for long in one spot inside a brake line, it is absorbed and diluted. According to your view of the system, brake fluid would never need changed I never said that, parts would never wear out and brake lines would never rust through. It is possible for moisture to wick into the system, yet fluid to not come out due to the very nature of the lip seals used in wheel cylinders, master cylinders and calipers. I agree, but I can't prove that, you are welcome to. I addressed by my mention previously water might enter the caliper/wheel cylinder by water immersion and/or wet driving, and parking the car wet before the moisture could be heated out of the seal area by driving/braking.
 
Last edited:
I'm all in on DOT 5. My '72 no rust Dart wouldn't have a hole in the floor, on the driver's side, from moisture absorbing brake fluid from a leaking master cyl if it had DOT 5 in there. Never use that crap again in my 3 old cars.
 
I converted my Austin-Healey to silicone fluid in the 1980s, first flushing the lines with isopropyl alcohol. Never had any leaking or any other problems since, but there is one downside to silicone. If you get it on painted surfaces and need to repaint them at sometime down the road, it's very difficult to get the fisheyes out of the paint. I converted my Charger to silicone after the restoration.
 
So, one fluid if spilled requires a repaint and the alternative fluid if spilled prevents a repaint?

Interesting :lol:

So who out there is spilling all this BF anyway?
 
Last edited:
j-c-c-62 said:
So, one fluid if spilled requires a repaint and the alternative fluid if spilled prevents a repaint?

Interesting :lol:

So who out there is spilling all this BF anyway?
Click to expand...
Exactly! I also have an MG Midget with silicone fluid and it required a repaint due to an engine bay fire. Seemed like no amount of sanding and cleaning would get rid of all the fisheyes (fortunately, in the engine bay only). Still, my belief is that silicone is less of a problem than DOT 3 or 4.
 
DOT-5 (silicone-based) brake fluid does not necessarily lower the durometer (hardness) of rubber seals or components
.

However, there's a crucial point to understand about DOT-5 and its interaction with older rubber seals:
  • If rubber seals have previously been exposed to DOT-3 or DOT-4 (glycol-based) brake fluids, switching to DOT-5 can cause the old seals to shed a surface layer of rubber, which can discolor the DOT-5 fluid. This is not a durometer issue but rather a compatibility problem that can affect the seal's integrity over time.
Additionally, it's important to note that DOT-5 is generally not recommended for modern vehicles due to:
  • Its tendency to trap air bubbles, leading to a spongy brake pedal.
  • Lower lubricity compared to glycol-based fluids, which might result in some weeping from seals.
  • Potential for damage to certain hydraulic components in older vehicles.

I ran DOT-5 in three of my vehicles about 30 years ago and foaming was an issue in all of them (my '48 Chrysler, my hemi-powered '34 ford and my Volare station wagon).
Everything else had DOT-3.

I never experienced foaming in my other vehicles but when the brakes got hot on mountain roads the three cars with DOT-5 were prone to brake failure due to foaming brake fluid, especially the big and heavy '48 Chrysler seven passenger sedan. My late wife was driving the '48 Chrysler and blew through an intersection getting off the interstate in Maryland (while following me in my '34 on the way to the Street Rod Nationals in Louisville, KY) when the brake fluid foamed from hard braking and the pedal suddenly went to the floor and nothing happened. Luckily, nobody was coming down the road when we got off the highway. The parking brake took a long time to get the car stopped.

After the car cooled down again the brake pedal felt normal and we took it real easy going down hills after that.

We flushed out the DOT-5 at the rod repair area once we got to Louisville and put in DOT-3 and never had an issue since then.

I switched the other cars over to DOT-3 and, aside from having to get my pressure bleeder out every 5 years or so to completely flush the systems, I haven't had any spongy pedals since switching over. Flushing's no big deal, either, and all seven of my registered vehicles get flushed every 5 years. Pressure bleeders are great!

As for the durometer issue, when I rebuilt the master cylinder on the '48 the packings were soft and spongy. The new ones were very firm right out of the box and have been in there roughly 30 years, now, without an issue.
 
Last edited:
I'm just happy no one said silicon brake fluid. :D
 
You must log in or register to reply here.

Similar threads

Migsbig
FOR SALE 1996 Dodge Viper GTS, CA
Replies
3
Views
2K
Migsbig
Migsbig
racingjim
4 Wheel Disc Conversion
Replies
2
Views
345
ckessel
ckessel
M
  • Locked
SOLD Brake Master Cylinder, Dist Valve + 2 lines
Replies
2
Views
763
mnewell337@gmai
M
F
Brake fluid seep from master cylinder
Replies
3
Views
605
tonysrt
T
M
Brake Issue Using Dot 5
2
Replies
36
Views
2K
mrhemi
mrhemi
Auto Transport Service
Back
Top