DOT 5 silicone

whats the deal on silicone brake fluid? heard it was no good? replacing everything on my new stocker, calipers hoses, lines etc. dry system

I been using it for over 20 years no issues

Been using it for 20 years in all my muscle cars. Doing so has certainly saved the paint on more than one. Works great with no problems.

works great for me

OK THANKS

I think dot 5 gets a bad rap from some people because it’s trickier to bleed. They never get all the air out which leads to a spongier pedal, and they blame that on the silicon fluid thinking it’s more compressible or something.
Silicon brake fluid retains air easier and takes longer for those air bubbles to rise up and out. To help when using it, pour it slowly out of the container into the reservoir to avoid it getting bubbly, and when pumping the brake pedal to bleed, push slowly to avoid frothing up the brake fluid like would happen if you pump the brakes vigorously.
Take your time, fully and properly bled the pedal will be as firm as when using dot 3.

Generally no problem, but let's not mix up the whole DOT rating with the "silicone" part of the fluid formulation.

Take a look at the attached files, this is a pretty good write-up that addresses both.

My takeaway is captured in the following quote (from the article):



Some pick up on that feel and do NOT like it, others do not, or if they do they do not object and are fine with the difference.

I have it in one of my cars and works fine for me. Whenever I get the other one back together it will get it also.

Strange...
After installation of the master cylinder, the brake system must be bled. Use only DOT 4 or DOT 5.1 brake fluid.

Mark Williams...
Use of DOT 4 or 5.1 fluid with a high boiling point and lubrication for seals and pistons is recommended. Do not use (DOT 5) silicone fluids .

TBM brakes...
Seal compatibility is critical to caliper performance. Very simply put, silicone brake fluid has a very undesirable effect on ethylene propylene rubber found in most brake systems. This tendency to swell the seals, combined with the fact that silicone is compressible when heated or in high altitudes creates unwanted changes to the pedal travel. Seal swelling can also cause brake lockup when used hard. Either of these changes in travel can be so extreme as to cause complete pedal loss or the vehicle dragging to a stop. Therefore, we highly suggest our DOT 5.1 Xtreme 6 fluid, or a comparable DOT 3 or 4 compatible fluid.

Wilwood...
Wilwood does not recommend using DOT 5 fluid in any racing applications. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200 degrees F, and at 212 degrees F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel.


I use DOT 5 in Harleys, which specify it and have systems designed for it.

Everything else for my use (drag race, street) gets DOT 4.

Not sure where everyone gets the idea that the silicone stuff is the hot lick.

been using dot 5 since the mid '90's. there was a post quite a few years back on this website about dot 5 screwing up the rubber stuff. took the brake system apart on the car that had been using dot 5 for about 10yrs and found absolutely no damage. i have no issues with dot 5 and will continue to use it.

Most of us that use it, because we have had our master cylinder leak and take out the painted firewall.

Absolutely. Silicone fluid hasn't been a problem with brake system rubber parts for decades!
I have it in my Dart and it works great. But I was very careful not to aerate the fluid and I bled it slowly and carefully.

A lot of those manufacturer disclaimers sound like legal CYA to me.
"Aeration and foaming" is a problem with ABS systems, otherwise it should not be happening under normal braking...

Now let the "But it will cause a fission reaction and explode, killing millions of people, if it's mixed with glycol fluids, even traces" begin...

My street cars have had it for over 30 years. My drag car 9 years. All stop fine w/o issue. The drag car has Will Wood brakes. If it was a road race car there may be and issue with repeated stops. But for street and Drag, no problem.
Doug

I have used dot 5 for many years with no problems. I like it on restorations and cars that sit a lot. I have a buddy who has a large car collection, I have seen cars restored and sit for several years and the brakes go bad just sitting with regular brake fluid. Dot 5 will not eat paint and does not draw moisture. But as several have said I see many manufactures of parts not recommending it's use. I got a set of calipers for a corvette the other day and it said use of Dot5 would void the warranty. Not really sure why the bad press for Dot5.

This is my all time favorite topic. And the BS surrounding this fluid is absolutely amazing.

My reply goes like this, can you imagine the legal liability of a company making a brake fluid that could kill you if used improperly? How about a companies liability for selling the same?

These rumors will never go away. Just too pervasive.

To the suggestion that silicon brake fluid damages brake seals, many brake assembly lubes for use when rebuilding calipers, master cylinders etc are silicon based.
Why would companies make a product that they know can damage the item customers are to use it on?
Petroleum based products damage brake seals not silicon.
Except Rolls Royces and general aviation aircraft brakes, they actually use petroleum based brake fluid and different type compatible seals.

one thing i see time and time again, are guys pumping the pi$$ out of the pedal, aerating the fluid and having trouble bleeding the system, no matter what brake fluid is being used.
i always just gently depress the pedal, open/close bleeder, then gently allow the pedal to rise.
while doing so, i have a clear hose attached to the bleeder, going into a small clear jar filled with enough fluid so the hose remains immersed in the fluid.
this has worked very well for me for over 50 years.
i just acquired a vacuum pump bleeder tool, so i will try it out the next time i need to bleed brakes.
just my experience, your mileage will vary.

There is so much hogwash circulating about DOT 5 fluid it's ridiculous. Even from manufacturers that should know better. Wilwood for example used to say never to use DOT 5 fluid in their calipers. Now they sell DOT 5 fluid with their own name on it.
And I agree that the assertion that DOT 5 silicone fluid can damage rubber seals is absolutely ridiculous. Going from my own experience, I rebuilt the brake system on my 1967 Olds 442 back in 1981. It still has the same fluid in it, and I've never had any issue whatsoever. That includes putting it into storage in 1987, and not getting it back out until 2010, and the brakes still functioned perfectly. And I have similar experience with several other vehicles. Never a problem. When I put wilwood brakes on my GTX race car back in 2003, wilwood was adamant that I could not use dot 5 silicone fluid with them. Well I did it anyway, and the same fluid is still in there with never a problem. Every vehicle that I rebuild the brakes gets converted. The track record on this stuff is just too good to not use it.

Regarding air bubbles and bleeding: yes it does have more of a tendency to pick up and retain air. So I do everything slow. I pour it into the master cylinder slowly and carefully to avoid creating bubbles. I don't pump up the pedal when bleeding. I have a helper slowly push it to the floor while I have the bleeder screw open, then I close the screw and have them slowly raise the pedal up to the top. And then repeat. Everything goes slow. And then I let it sit at least overnight, or longer if I have time. After it is sat overnight, I take the cover off of the master cylinder and slightly jiggle the brake pedal. Bubbles will rise out of the ports in the bottom of the master cylinder. Because the air has collected there. And I just slowly, gently jiggle the pedal until bubbles stop rising. If I have time I'll let it sit overnight again and repeat the process until no air rises. Working it this way I have a brake pedal that is as firm as in any other car.

Every car, without exception, that I have let sit around for more than 4 years, sometimes a lot less, with hygroscopic DOT 3 fluid, has a failed hydraulic system when I retrieve it. As stated above, the silicone fluid completely eliminates that issue.

In the interest of full disclosure, I should mention my single negative experience, though. I fabricated a hydraulic clutch linkage (using an external pull-type slave cylinder, from Howe Racing Products). Filled the clutch reservoir with DOT 5 also. Car sat for several months.

When I went to fire it up, the clutch pedal went to the floor. Discovered the reservoir was empty! All the fluid had leaked past the seals, so whatever that company used was not "silicone-safe". I replaced the o-rings, flushed the master, and refilled with DOT 4. It's been working fine for the last couple of years. I'll just have to remember to change it now and then.

Brakes are perfect after several years, though.