DOT 5 & Seals

[runk]

british cars and DOT 5

We (along with most I know in the hobby) switch our old British sports cars over to DOT 5 when we do a full rebuild of the brake system. As some others have said, it's almost impossible to flush all the DOT 3 out of the system. Added benefit of the DOT 5, it does not destroy paint.

 

[akonitony]

That is the main reason I am keeping the DOT 5 in my truck. I just rebuilt the entire front end and painted it while I was at it. I also am replacing the master cylinder and brake calipers and don't want to have all that paint slough off due to a spill from the master cylinder. I honestly don't know why anyone would want to downgrade from DOT 5 to 3.

 

[Marlboro]

Question, How can one tell if they have dot 5 or dot 3 in there system? I 've got a deuce and checked the mc for the first time it was a little low so i went and bought a small bottle of Dot 5... The mc has a very light brown brake fluid in it and the new dot5 was light purple. I didnt add any because i didn't wanna find out later that i mixed it... So is there a way to tell which i have ???

 

[stumps]

Question, How can one tell if they have dot 5 or dot 3 in there system? I 've got a deuce and checked the mc for the first time it was a little low so i went and bought a small bottle of Dot 5... The mc has a very light brown brake fluid in it and the new dot5 was light purple. I didnt add any because i didn't wanna find out later that i mixed it... So is there a way to tell which i have ???

First, there should be a 3x5 inch (approx) yellow label near the door for the master cylinder that says DOT5 only.

Take your finger, and dip it into the master cylinder sump, and then dip your finger into a glass of water. If it is DOT 3, the slippery feeling of the fluid will simply vanish as you rub your fingers together, and the color will disperse quickly into the water. If it is DOT5, the liquid that was on your finger will now be beaded up and floating on the surface of the water.

Also, DOT 5, from the can, has no taste or odor. DOT 3, from the can, is sweet, poisonous (a touch on your tongue won't hurt you), and smells a little like tempera (watercolor) paint.

DOT 5 comes in two colors: Purple and Yellow. It starts out purple, but if subject to DOT 3, or water, the purple color is stolen by the DOT 3, or water. Brown is a classic color for wet DOT 3... the brown color is rust from the master cylinder's cast iron body.

-Chuck

 

[Marlboro]

Thank you, the yellow label is there and reads something like this " use only military spec. silicone brake fluid #--------" I will try what you suggested later today...Again Thank You

 

[m1010plowboy]

Dot 5 and older seals

Guys guys guys, we need to talk. Gander the M135 was re-built over a decade ago and we're lucky enough to tear it down after the MC started leaking recently.

The rubber seals on the MC that was rebuilt with Dot 5 were softened and friable. They'd fall apart when touched and I will get pics of those up soon.

Is this "Older 50's / 60's rubber" not compatible with the new silicone fluids?


We pulled apart a few that we know had Dot 3 and the rubber seems re-usable. We did find a few kits around but I'd really like to avoid ruining any more so the Dot 3 vs 5 decision puts that confused look on our faces again.




We've only got one hub off and the wheel cylinders don't seem to be compromised so there is something different about the rubber. The wheel cylinders could have 80's or 90's rubber boots and seals and that may be why they're still ok. .....but we don't know.


What's the latest info we can add to this ancient Hot Rod post?

 

[m1010plowboy]

11 year old posts have some fantastic info in them. Post #8 by CGarbee is great, just great. https://www.steelsoldiers.com/showthread.php?10484-Dot-3-or-Dot-5-Brake-fluid

""""""""If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers."""""""

 

[rustystud]

I've been a big proponent of DOT 5 (Silicone) brake fluid for decades now. I've used it in almost all my vehicles, unless it has had anti-lock brakes installed on it. One of the biggest mistakes I've seen people do is failure to "totally" clean the brake system ! Also "ALL" rubber seals must be replaced if converting to silicone. The seals will absorb the brakes fluid so if you previously had DOT 3 in the system the seals will also. Then when you convert to Silicone DOT 5 you will get destroyed seals !
There is nothing evil about DOT 5 and it really has more advantages then either DOT 3 or DOT 4 . It will actually help lubricate the seals and allow then to last much longer then normal. The silicone fluid will last for decades and only needs a "little" bleeding out every 2 years to prevent water build-up. No need to "completely" replace all the fluid unlike DOT 3 or DOT 4.
I posted my front brake caliper rebuild on my M1024 last year. I had rebuilt that caliper over 20 years ago and with the silicone fluid it was still in excellent shape ! I could have easily reused the piston seal and had no problems. I rebuilt it just to check on it.
So, the bottom line is you need to do your "due diligence" when rebuilding a brake system that will be using Silicone DOT 5 brake fluid.

 

[brianp454]

As usual, Rusty is spot on!

 

[Floridianson]

11 year old posts have some fantastic info in them. Post #8 by CGarbee is great, just great. https://www.steelsoldiers.com/showthread.php?10484-Dot-3-or-Dot-5-Brake-fluid

Thanks that post was very good reading even if it was 11 years old. Just about the same thing through the years about Dot 5 and old news is still good news.

 

[m1010plowboy]

Dot 5 stored indoors since new.

Not great follow-up photos but good enough for the girls we go with. This is the MC piston with the decayed rubber seal.



There were a few black particles in the fluid but the rubber on the shiny, 10 year old, rear cylinders feels new. This truck had a lot of sitting time and as far as we know has never been outside of a heated shop. We can be humid but this doesn't look like 'water collecting in a low spot and freezing' symptom as we've seen in other reports.





There's still that nitrile possibility that old rubbers don't like Dot 5 and eventually go away. She's getting flushed and juiced back up with DOT 3 as per the manual and owners desire. I'll report back in a few years.

 

[rustystud]

Not great follow-up photos but good enough for the girls we go with. This is the MC piston with the decayed rubber seal.

View attachment 737064

There were a few black particles in the fluid but the rubber on the shiny, 10 year old, rear cylinders feels new. This truck had a lot of sitting time and as far as we know has never been outside of a heated shop. We can be humid but this doesn't look like 'water collecting in a low spot and freezing' symptom as we've seen in other reports.

View attachment 737063



There's still that nitrile possibility that old rubbers don't like Dot 5 and eventually go away. She's getting flushed and juiced back up with DOT 3 as per the manual and owners desire. I'll report back in a few years.



View attachment 737062View attachment 737065

Silicone will do no harm to "Nitrile" seals. The problems arise from using old seals when the manufacturer used a brake fluid rebuild additive to keep the seals "fresh" . I've seen this many times before. To keep the seals from drying out there is a protective coating added from the factory. This coating must be removed if your using DOT 5 silicone brake fluid. The problem here is that the seals actually "absorb" some of the protective additive. You can actually "feel" this coating when you rub the seal in question. It has a really smooth finish like "vasoline" had been rubbed on it then wiped clean. Since I only use more modern seals in all my brake systems I have never had this problem.
If you ever try and use DOT 5 in an older system again, I would go with modern "repop" seals instead of older "original" seals.